Method of covering at least part of a wall, use of a plurality of panels, panel, and assembly of a plurality of panels and a wall

Abstract

Method of covering at least part of a wall (4) of a building by means of a plurality of panels. Individual panels (2) each include a panel body (6) and have a panel front surface, a panel back surface, and a panel peripheral surface (12). The method includes positioning the plurality of panels along the wall (4). The panel bodies are spaced apart from each other for having a peripheral gap (14) between the panel bodies (6). At least part of the panel back surfaces are spaced apart from the wall (4) for having a wall gap (16) between the panel bodies (6) and the wall (4). The method includes realising in the wall gap (16) and / or the peripheral gap (14) absorption of low-frequency acoustic noise (18) that is generated outside of the building and that propagated towards the wall (4) to reach the wall gap (16) and / or the peripheral gap (14).

Description

FIELD

[0001] The invention relates to a method of covering at least part of a wall of a building by means of a plurality of panels. The invention also relates to use of a plurality of panels for covering at least part of a wall of a building. The invention further relates to a panel that is arranged for covering at least part of a wall of a building. The invention further relates to an assembly of a plurality of panels and a wall of a building, wherein the plurality of panels covers at least part of the wall of the building.BACKGROUND

[0002] Many urban areas have grown to accommodate large amounts of inhabitants and, in particular during working hours, employees. In many cases their numbers are still growing. At the same time, nowadays, available opportunities for urban areas to expand can be limited, e.g. as a result of protection of nature or because of costs involved in such expansion. As a result of such developments, nowadays people may be living and working closely together. The environments of residential buildings, office buildings, and also other types of buildings, and also such buildings itself, may not always be adapted to cope with this.

[0003] At the same time, since a couple of years there is a tendency for people to work from home at least part of the time. Working from home was even mandatory for many employees during part of the COVID pandemic. Although this may partly neutralize urban areas to become more crowded with employees, it does increase the requirements to the environment of residential buildings. A requirement for people when living and / or working in a building, is an acceptable level of acoustic noise in its environment. This may especially be true for people working from home in a relatively small space, and who wish to go outside of the building during breaks.

[0004] A particular type of acoustic noise is low-frequency acoustic noise. Although other definitions exist, low-frequency acoustic noise may be defined as acoustic noise with a frequency in the range from 20 Hertz to 100 Hertz. While for some people such noise may be tiresome, for other people such noise may even be detrimental to their health (see: G. Leventhall, "Low Frequency Noise. What we know, what we do not know, and what we would like to know", Journal of Low Frequency Noise, Vibration and Active Control, 2009, volume 28, number 2, page 79-104).

[0005] Causes for low-frequency acoustic noise are sometimes unclear, for example because low-frequency acoustic noise can travel over large distances. So, it may be difficult to tackle the problem at the source, as the source may be unknown and difficult to discover. Moreover, it normally is difficult to protect oneself from low-frequency acoustic noise. Earplugs for example can be considered to be not always effective, as low-frequency acoustic noise may still be able to reach the inner ear through bone tissue. Low-frequency acoustic noise forms a problem on its own, separate from acoustic noise at higher frequencies against which one can personally protect oneself better.

[0006] It may thus be clear that there is a need to at least reduce a level of low-frequency acoustic noise in an environment of a building.SUMMARY

[0007] The invention provides a method of covering at least part of a wall of a building by means of a plurality of panels, wherein individual panels of said plurality of panels each include a panel body and have a panel front surface, a panel back surface, and a panel peripheral surface, the method including: positioning the plurality of panels along the wall so that the panel front surfaces face away from the wall, wherein, after the positioning, the panel bodies of the plurality of panels are spaced apart from each other for having a peripheral gap between the panel bodies, and wherein, after the positioning, the panel back surfaces of the plurality of panels are at least partly spaced apart from the wall for having a wall gap between the panel bodies and the wall.

[0008] According to an aspect, the method includes: realising in the wall gap and / or the peripheral gap, by means of the positioning of the plurality of panels, absorption of low-frequency acoustic noise that is generated outside of the building and that propagated towards the wall to reach the wall gap and / or the peripheral gap. According to a further aspect, the method includes: realising, by means of the positioning of the plurality of panels, a reduction of reflection in a direction away from the wall of the building and / or a reduction of transmission into the wall of the building, of low-frequency acoustic noise that is generated outside of the building and that propagated towards the wall to reach the wall gap and / or the peripheral gap.

[0009] Preferably, the low-frequency acoustic noise has a frequency that is at most 100 Hertz. Preferably, the low-frequency acoustic noise has a frequency that is at least 20 Hertz. In an embodiment, frequencies of the low-frequency acoustic noise are in a range from 20 Hertz to 100 Hertz. It was surprisingly found in experiments and numerical simulations that absorption of low-frequency acoustic noise can be realised by dimensioning the panels, the wall gap, and the peripheral gap for that purpose. Without intending to be bound by theory, it is believed that low-frequency acoustic waves may partly cancel out and / or dissipate in the wall gap and / or the peripheral gap. As a result of the absorption, a level of low-frequency acoustic noise in an environment of the building can be reduced.

[0010] In embodiments wherein one or more other buildings are present in an environment of the building, the reduction of low-frequency acoustic noise in an environment of the building can be expected to have a positive effect on noise levels inside the one or more other buildings. After all, if a level of low-frequency acoustic noise in an environment of the building can be reduced, it may be expected that a level of low-frequency acoustic noise is reduced inside the one or more other buildings as well. As a result of the reduced level of low-frequency acoustic noise in said environment, less low-frequency acoustic energy may be available for transmission into the one or more buildings. While low-frequency acoustic noise may be detrimental to one's wellbeing outside of a building, it may also be damaging inside buildings where people stay for many hours each day, such as office buildings and residential buildings.

[0011] Preferably, the panel peripheral surface connects, and / or extends in between, the panel front surface and the panel back surface. Preferably, the panel body has a planar shape. Preferably, a thickness of the panel body varies at most 30 percent of a maximum value of the panel body thickness, more preferably varies at most 15 percent or at most 10 percent of a maximum value of the panel body thickness. The plurality of panels does not necessarily include all panels that cover the at least part of the wall of the building. Optionally, some panels covering the at least part of the wall are not included in said plurality of panels. Preferably, the plurality of panels form one or more groups of neighbouring panels that are separated from at least one other panel of the same group only by the peripheral gap. Preferably, the panel peripheral surfaces of the plurality of panels are spaced apart from each other for having the peripheral gap between the panel peripheral surfaces. Preferably, the panel back surface of the individual panels faces the wall.

[0012] In an embodiment, the individual panels of the plurality of panels are similar, or substantially equal, to each other. Preferably, each of the individual panels has a panel body, a panel front surface, a panel back surface, and a panel peripheral surface that is similar, or substantially equal, to respectively the panel body, the panel front surface, the panel back surface, and the panel peripheral surface of the other individual panels. In another embodiment, one or more of the individual panels has a shape and / or size that differs from one or more other ones of the individual panels. Optionally, a width of the peripheral gap at the panel front surface between a pair of panels of the plurality of panels, may differ at least 20 percent from a width of the peripheral gap between another pair of panels of the plurality of panels. Such variations may influence, in particular may lead to a broadening of, the absorption spectrum of the low-frequency acoustic noise.

[0013] Preferably, the panels each have a panel body that is made of a porous material, or includes at least 50 weight percent or at least 80 weight percent of a porous material. Preferably, said porous material is a fibre cement material. Preferably, a density of the porous material is at least 1200 kilogram per cubic metre and / or is at most 2200 kilogram per square metre. More preferably, the density of the porous material is at least 1600 kilogram. Preferably, the porous material has a porosity of at least 10 volume percent and / or at most 40 volume percent. More preferably, the porous material has a porosity of at least 14 percent and / or at most 24 percent. Preferably, a porosity of the porous material, or at least a porosity of a majority of the porous material, is connected so that the material is permeable.

[0014] The positioning of the plurality of panels along the wall preferably includes attaching the plurality of panels to a frame. The positioning of the plurality of panels along the wall preferably includes attaching the frame to the wall, before or after the panels are attached to the frame. Optionally, the frame is positioned at least partly in the wall gap. In an embodiment, the panels are attached directly to the wall without using the frame.

[0015] In an embodiment, the panel body of each of the individual panels has a planar panel dimension in a direction along the panel front surface of the individual panel. Preferably, the method includes: arranging the planar panel dimension of the plurality of panels, the peripheral gap, and the wall gap so that the absorption of low-frequency acoustic noise that propagated towards the wall to reach the wall gap and / or the peripheral gap, is realised. Preferably, the method includes: arranging the planar panel dimension of the plurality of panels, the peripheral gap, and the wall gap so that the reduction of reflection of low-frequency acoustic noise in a direction away from the wall of the building is realised and / or the reduction of transmission of low-frequency acoustic noise into the wall of the building is realised. Preferably, the planar panel dimension is directed along the front surface of an individual panel.

[0016] In an embodiment, the method includes: arranging the planar panel dimension of the plurality of panels, the peripheral gap, and the wall gap so that low-frequency acoustic noise that propagated towards the wall to reach the wall gap and / or the peripheral gap, at least partly cancels out and / or dissipates in the wall gap and / or the peripheral gap, so that the absorption of low-frequency acoustic noise is realised, the reduction of reflection of low-frequency acoustic noise in a direction away from the wall of the building is realised, and / or the reduction of transmission of low-frequency acoustic noise into the wall of the building is realised. By choosing dimensions of the peripheral gap, the wall gap, and the planar panel dimension of the individual panels of the plurality of panels, absorption, in particular by cancellation and / or dissipation, of part of the low-frequency acoustic noise may be achieved.

[0017] In an embodiment, the panel bodies of the plurality of panels each include a central panel body part, wherein the planar panel dimension extends from the central panel body part to the panel peripheral surface. For example, the planar panel dimension equals half of a width, half of a length, or half of a diameter of a panel body. Preferably, the method includes: arranging the planar panel dimension of the plurality of panels, the peripheral gap, and the wall gap so that a maximum of the absorption of low-frequency acoustic noise is realised at a main absorption frequency of the low-frequency acoustic noise. Preferably, the planar panel dimension is at least 20 Hertz metre divided by said main absorption frequency and / or is at most 160 Hertz metre divided by said main absorption frequency. Optionally, the planar panel dimension ranges from the central panel body part to the panel peripheral surface. Preferably, for at least one of the individual panels, for a majority of the individual panels, or for each of the individual panels, a minimum distance between open parts of the peripheral gap that are at opposite sides of the panel body, and that optionally can be connected by a straight line that goes through the central part of the panel body, is at most 1,3 metre.

[0018] Preferably, said main absorption frequency is at least 20 Hertz and / or at most 100 Hertz, more preferably is at least 40 Hertz and / or at most 90 Hertz. In particular, the main absorption frequency may be in a range from 50 Hertz to 80 Hertz, for example in a range from 60 Hertz to 70 Hertz. Experiments and numerical simulations that were carried out, indicate that, in an embodiment, a reduction of at least about 30 percent can be reached at a main absorption frequency of about 63 Hertz. Preferably, the main absorption frequency is above an audible frequency threshold above which low-frequency acoustic noise is audible for at least some people, preferably for a majority of the people, being confronted with the low-frequency acoustic noise. At least in such embodiments, a reduction in amplitude of the acoustic noise may be appreciated. In an embodiment, at the main absorption frequency, the absorption of acoustic energy, or an absorption coefficient of the plurality of panels, is at least 20 percent, preferably is at least 30 percent, more preferably is at least 40 percent. In particular, at the main absorption frequency, the absorption of acoustic energy, or an absorption coefficient of the plurality of panels, may be at least 50 percent or may be at least 60 percent.

[0019] In an embodiment, the peripheral gap at least partly surrounds the individual panel bodies of the plurality of panels. Preferably, the peripheral gap completely surrounds at least one of, more preferably a majority of, the panel bodies of the plurality of panels. Preferably, the peripheral gap is open or is at least partly open. Preferably, in an open or partly open peripheral gap, air can move into and out of the peripheral gap.

[0020] In one implementation, the panel comprises four peripheral surfaces and the peripheral gap is open along two out of said four peripheral surfaces, but is closed along the other two peripheral surfaces. In a preferred option, the panel has a rectangular or square shape, and the said open gaps are arranged in parallel. More preferably, the gaps extending in the horizontal direction, thus typically between overlying rows of panels, are open, whereas the gaps extending in the vertical direction, thus typically between adjacent panels within a single row, are closed. While it may be beneficial to have an open gap extending fully around the panel, it is deemed practical for sake of fastening and / or decorative purposes that merely the gaps extending in the horizontal direction are open. This facilitates that a vertically extending frame portion can be present behind said closed gap.

[0021] In a further implementation, the assembly of panels arranged along the wall, which assembly is typically referred to as exterior facade, comprises at least a first row, a second row and a third row of panels, wherein a first open gap is present between the first row and the second row, and wherein a second open gap is present between the second row and the third row. It has been found in investigations leading to the invention, that the low noise absorption is significantly larger, when a first and a second open gaps are present above each other.

[0022] Preferably, at the panel front surface, the peripheral gap width is in a range from 4 millimetre to 16 millimetre. More preferably, at the panel front surface, the peripheral gap width is in a range from 6 millimetre to 14 millimetre. The peripheral gap width may for example be about 1 centimetre, at the panel front surface. In a variation, the peripheral gap width at the panel front surface is at least 4 millimetre or at least 6 millimetres, and / or is at most 14 millimetre or at most 16 millimetres. In a variation, the peripheral gap width at the panel front surface is at most 20 millimetres. In a variation, the peripheral gap width at the panel front surface is at most 6 millimetres or is at most 4 millimetres. Preferably, values of the width of the peripheral gap refer to the width of the peripheral gap along a majority of the peripheral gap, preferably along at least 80 percent of the peripheral gap. Optionally, the width of the peripheral gap refers to an average width along the peripheral gap.

[0023] Preferably, a width of the wall gap is at least 50 millimetres and / or at most 400 millimetres. More preferably, the width of the wall gap is at least 100 millimetres and / or at most 300 millimetres. For example, the width of the wall gap is about 0,2 metre. Preferably, the values of the width of the wall gap refer to the width of the wall gap along a majority of the wall gap, preferably along at least 80 percent of the wall gap. Preferably, values of the width of the wall gap disclosed herein refer to the width of the wall gap at a majority, preferably at least 80 percent, of positions where the wall is covered by the plurality of panels. Optionally, the width of the wall gap refers to an average width of the wall gap at positions where the wall is covered by the plurality of panels.

[0024] Preferably, the planar panel dimension, such as e.g. a width or length of the individual panels or about half of the width or length, is at least 300 millimetre and / or is at most 4000 millimetre. For example, the planar panel dimension is approximately 1 metre or approximately 1,5 metre. Experiments and numerical simulations that were carried out indicate that, at least, a peripheral gap width of at least 6 millimetre and / or at most 14 millimetre, a width of the wall gap of at least 100 millimetre and / or at most 300 millimetre, and a width and / or length of a rectangular panel of at least 500 millimetre and / or at most 3000 millimetre, can be expected to enable a significant absorption of low-frequency acoustic noise.

[0025] In an embodiment, the panel body of each of the individual panels has a perimeter that is defined by the panel peripheral surface of the panel body. Preferably, the peripheral gap is open along the perimeter of at least one, preferably of a majority, more preferably of each, of the individual panels, so that the low-frequency acoustic noise can propagate through the open peripheral gap. Preferably, the peripheral gap is open along a part of the perimeter, or along at least part of the perimeter, so that low-frequency acoustic noise can propagate through the open part of the peripheral gap. Preferably, the peripheral gap is open along at least 20 percent, at least 50 percent, or at least 80 percent, of the perimeter so that the low-frequency acoustic noise can propagate through the open part of the peripheral gap.

[0026] In an embodiment, the peripheral gap may be substantially open for parts of the peripheral gap that extend in a substantially sideward direction, while the peripheral gap may be substantially closed for parts of the peripheral gap that extend in a substantially upward direction. In such an arrangement, it may be more difficult for rain to enter the wall gap. As another example, the peripheral gap may be substantially open for parts of the peripheral gap that extend in a substantially upward direction, while the peripheral gap may be substantially closed for parts of the peripheral gap that extend in a substantially sideward direction.

[0027] In an embodiment, the peripheral gap extends in a longitudinal peripheral gap direction in between at least two panel bodies of said plurality of panels. Preferably, the peripheral gap has a peripheral gap width in a direction that is transverse to said longitudinal peripheral gap direction and that is directed from one of the at least two panel bodies to another one of the at least two panel bodies. For example, the direction of the peripheral gap width may be along the panel front surfaces of the at least two panels and / or along the panel back surfaces of the at least two panels. Preferably, along at least part of the peripheral gap, the peripheral gap width increases along a propagation direction of said low-frequency acoustic noise through the peripheral gap towards the wall. Preferably, at the panel front surface the peripheral gap width is smaller than the peripheral gap width at the panel back surface along at least part of the peripheral gap, for example along at least 20 percent of the peripheral gap, along at least 50 percent of the peripheral gap, or along at least 80 percent of the peripheral gap. Such preferred configurations of the peripheral gap width may increase an absorption of low-frequency acoustic noise by means of the panels, while the peripheral gap width at the panel front surface can be kept limited. Such a configuration of the peripheral gap may further hide the wall from view and could also be beneficial in view of regulations on the peripheral gap width at the panel front surface that regulate the peripheral gap width. In particular for a peripheral gap that has a constant width along a direction perpendicular to the panel front surface, such regulations could diminish an effectiveness of the absorption of low-frequency acoustic noise.

[0028] In an embodiment, along at least part of the peripheral gap, a width of the peripheral gap increases along a direction through the peripheral gap towards the wall. Preferably, along at least 20 percent, at least 50 percent, or at least 80 percent, of the peripheral gap, the width of the peripheral gap increases along the direction through the peripheral gap towards the wall.

[0029] In an embodiment, the panel peripheral surfaces of the individual panels are oblique relative to the panel front surfaces of the individual panels along at least part of the peripheral gap, and optionally along substantially the whole peripheral gap. In an embodiment, the panel peripheral surface of at least one, preferably of a majority, more preferably of each, of the individual panels is, along at least part of the peripheral gap, oblique relative to the panel front surface. Preferably, along the at least part of the peripheral gap, an angle between the panel peripheral surface and the panel front surface of the individual panels is in a range from 20 degrees to 70 degrees. Preferably, along the at least part of the peripheral gap, for example along at least 20 percent of the peripheral gap, preferably along at least 50 percent of the peripheral gap, or more preferably along at least 80 percent of the peripheral gap, an angle between the panel peripheral surface and the panel front surface of the at least one individual panel, of the majority of the individual panels, or of each individual panel, is in a range from 20 degrees to 70 degrees, preferably is in a range from 30 degrees to 60 degrees, for example is about 45 degrees. As a result, in an embodiment, at the panel front surface the peripheral gap width may be smaller than the peripheral gap width at the panel back surface. Preferably, at the panel back surface, the peripheral gap width is at least 1,2 times, preferably at least 1,5 times, more preferably at least 2 times or at least 3 times, the peripheral gap width at the panel front surface along the at least part of the peripheral gap, e.g. along at least 30 percent of the peripheral gap. Said angle, said obliqueness, and / or said difference between the peripheral gap width at the panel front surface and the peripheral gap width at the panel back surface, preferably extend along at least 50 percent of the peripheral gap.

[0030] In an embodiment, the panel peripheral surfaces of the individual panels are, at least partly or substantially completely, oblique relative to the panel front surfaces of the individual panels along open parts of the peripheral gap. Preferably, the panel peripheral surfaces of the individual panels are, at least partly or substantially completely, at a substantially right angle relative to the panel front surfaces of the individual panels along closed parts of the peripheral gap. In an embodiment, the panel bodies of the plurality of panels each have a panel peripheral surface that is, relative to the panel front surface, oblique along part of the panel peripheral surface and at a substantially right angle along another part of the panel peripheral surface. A panel peripheral surface that is at such a substantially right angle may be more easily closed and / or may be less easily damaged during the closing of the peripheral gap. A panel peripheral surface having an oblique angle may increase the absorption of low-frequency acoustic noise while still meeting regulations with respect to an allowable width of the peripheral gap.

[0031] In an embodiment, the panel bodies of the plurality of panels each have at least three, preferably four or at least four, corners and have a panel peripheral surface that is, relative to the panel front surface, oblique along part of the panel peripheral surface. In an embodiment, said panel peripheral surface is at a substantially right angle to the panel front surface at at least one of the corners, preferably at a pair of the corners, more preferably at all of the corners, of each of the panel bodies. Preferably, for each of the individual panels, in between at least one pair of the corners the panel peripheral surface is partly oblique relative to the panel front surface, preferably is oblique relative to the panel front surface along at least 20 percent, at least 50 percent, or at least 80 percent of a distance between said pair of corners. Preferably, the pair of corners, and / or the at least one pair of corners, is formed by corners that are neighbouring to each other. Having such a substantially right angle at one or more corners could lead to a less vulnerable panel.

[0032] In an embodiment, the plurality of panels each have a rectangular shape, said rectangular shape defining a longitudinal panel direction of the panels. According to an option, parts of the panel peripheral surfaces that extend along the longitudinal panel direction are oblique relative to the panel front surfaces, while the panel peripheral surfaces that extend transverse to the longitudinal panel direction are at a substantially right angle relative to the panel front surfaces. According to another option, parts of the panel peripheral surfaces that extend in a direction that is transverse to the longitudinal panel direction are oblique relative to the panel front surfaces, while the panel peripheral surfaces that extend in the longitudinal panel direction are at a substantially right angle to the panel front surfaces. Both options enable parts of the panel peripheral gap that extend in one, preferably substantially horizontal or otherwise sideward, direction to be open and be provided with an oblique panel peripheral surface, while parts of the panel peripheral gap that extend in another, preferably substantially vertical or otherwise upward, direction are closed.

[0033] In an embodiment, the method includes providing, in the wall gap, a damping material that is arranged for damping the low-frequency acoustic noise. Preferably, said damping material is a mineral wool such as rock wool. Preferably, a majority of the wall gap is filled with the damping material. The damping material may further promote the absorption of the low-frequency acoustic noise in the wall gap. Thus, preferably, mineral wool or another material that can dampen low-frequency acoustic noise, is provided in the wall gap.

[0034] In an embodiment, the panel back surface of at least one, preferably of a majority, more preferably of each, of the individual panels is provided with a ridge. Preferably, the at least one ridge or the ridges, after the positioning of the plurality of panels, partitions the wall gap in order to create at least two cavities in the wall gap. Preferably, the at least two cavities are in fluid communication with the peripheral gap so that the low-frequency acoustic noise can propagate through the peripheral gap into the cavities in the wall gap. Optionally, by means of the one or more ridges, the panels are attached to the wall, optionally without using the frame. Preferably, the method includes positioning the one ore more ridges in contact with the wall. The at least one ridge enables to adjust acoustic properties of the wall gap. The at least one ridge may enable a better control of the absorption of acoustic noise. Preferably, the at least two cavities have volumes that differ from each other, so that a resonance frequency of one of the at least two cavities is different from, e.g. is at least 120 percent of, another one of the at least two cavities. Instead of one main absorption frequency in the low-frequency range, more than one main absorption frequency may be obtained as a result of the cavities having different acoustic properties. Thus, optionally, a broader frequency range may be obtained wherein the absorption of low-frequency acoustic noise is significant.

[0035] In an embodiment, the ridge is formed by the frame to which the plurality of panels is attached or is to be attached. In an embodiment, the frame may be designed for partitioning the wall gap for forming the at least two cavities. In another embodiment, the ridge is part of the panel, e.g. is integral to the panel. For example, the ridge and the remainder of the panel can be made of one part. The ridges may be attached to the panels before the panels are attached to the frame and / or to the wall. Optionally, a number of ridges of the plurality of panels are part of a panel and a number of ridges are formed by the frame.

[0036] In an embodiment, the wall faces another wall that is covered by means of a method according to the invention, so that low-frequency acoustic noise that is reflected from the wall can propagate towards said other wall. The wall and the other wall may for example be at opposite sides of a street. The wall and the other wall may for example be part of separate buildings. In an embodiment, along the street, a plurality of buildings (or, in other words, a group of buildings) is provided. The method may include covering at least part of a wall of each building of the plurality of buildings using a method according to the invention, so that low-frequency acoustic noise that is reflected from the wall of one building of the plurality of buildings can propagate towards the wall of another building of the plurality of buildings. Preferably, the wall of said one building and the wall of said another building both face the street. If reflected acoustic noise is also absorbed by means of a plurality of panels on said another building, reducing the amplitude of the low-frequency acoustic noise in an environment of both buildings may be realised effectively.

[0037] In an embodiment, the planar panel dimension, the peripheral gap and / or the wall gap of the plurality of panels positioned along the wall is different from, e.g. is at least 120 percent of, respectively the planar panel dimension, the peripheral gap and / or the wall gap of the plurality of panels along the other wall. Preferably, a frequency of low-frequency acoustic noise at which a maximum in the absorption is reached by means of the plurality of panels covering the wall, is different from, e.g. is at least 120 percent of, another frequency of low-frequency acoustic noise at which a maximum in the absorption is reached by means of the plurality of panels covering the other wall. Preferably, a frequency of the low-frequency acoustic noise at which a maximum of the reduction of the reflection from and / or transmission through the wall is reached, is different from, e.g. is at least 120 percent of, a frequency of the low-frequency acoustic noise at which a maximum of the reduction of the reflection from and / or of the transmission through the other wall is reached. In such an embodiment, preferably, a difference between said frequency and said other frequency is at least 30 Hertz, more preferably at least 50 Hertz. In these embodiments, the low-frequency acoustic noise may be absorbed more evenly along a wider frequency range, compared with the situation that both the wall and said other wall are covered in the same way.

[0038] Preferably, the plurality of panels forms a facade covering the at least part of the wall of the building. Preferably, the facade has an aperture ratio that is defined as the ratio of an area, measured along the panel front surfaces, of an open part of the facade, preferably formed by the open part of the peripheral gap, and a closed part of the facade, preferably formed by the plurality of panels. In an embodiment, the facade has an aperture ratio of at most 0,02, preferably at most 0,01, more preferably at most 0,005. Significant absorption effects were found in experiments wherein an aperture ratio was in a range from 0,002 to 0,007. Preferably, the facade has an aperture ratio of at least 0,001, optionally of at least 0,002, at least 0,003, or at least 0,004.

[0039] The invention also provides use of a plurality of panels for covering at least part of a wall of a building, wherein individual panels of said plurality of panels each include a panel body and have a panel front surface, a panel back surface, and a panel peripheral surface, the use including: positioning the plurality of panels along the wall so that the panel front surfaces face away from the wall, wherein, after the positioning, the panel bodies of the plurality of panels are spaced apart from each other for having a peripheral gap between the panel bodies, and wherein, after the positioning, the panel back surfaces of the plurality of panels are at least partly spaced apart from the wall for having a wall gap between the panel bodies and the wall. Preferably, such use is combined with one or more embodiments, features, variations, or examples of a method disclosed herein.

[0040] According to an aspect, the use includes: realising in the wall gap and / or the peripheral gap, by means of the positioning of the plurality of panels, absorption of low-frequency acoustic noise that is generated outside of the building and that propagated towards the wall to reach the wall gap and / or the peripheral gap. According to a further aspect, the use includes: realising, by means of the positioning of the plurality of panels, a reduction of reflection in a direction away from the wall of the building and / or a reduction of transmission into the wall of the building, of low-frequency acoustic noise that is generated outside of the building and that propagated towards the wall to reach the wall gap and / or the peripheral gap.

[0041] The invention also provides a panel that is arranged for covering at least part of a wall of a building, wherein the panel includes a panel body and has a panel front surface, a panel back surface, and a panel peripheral surface. Preferably, the panel is arranged for being positioned along the wall so that the panel front surface faces away from the wall and at least part of the panel back surface is spaced apart from the wall. Preferably, at least part of the panel peripheral surface is oblique relative to the panel front surface. Preferably, an angle between the panel peripheral surface and the panel front surface is in a range from 20 degrees to 70 degrees. Thus, preferably, the panel peripheral surface is, along at least part of the panel peripheral surface, oblique relative to the panel front surface. Preferably, along the at least part of the panel peripheral surface, an angle between the panel peripheral surface and the panel front surface is in a range from 20 degrees to 70 degrees.

[0042] According to an aspect, the wall gap and / or the peripheral gap is arranged for absorbing low-frequency acoustic noise that is generated outside of the building and that propagated towards the wall to reach the wall gap. According to a further aspect, the wall gap and / or the peripheral gap is arranged for reducing reflection in a direction away from the wall of the building and / or reducing transmission into the wall of the building, of low-frequency acoustic noise that is generated outside of the building and that propagated towards the wall to reach the wall gap and / or the peripheral gap.

[0043] In an embodiment, the panel is one of a plurality of panels, wherein the individual panels of the plurality of panels preferably are similar. Preferably, the features of the panel are also implemented in each other panel of the plurality of panels. This plurality of panels can be used in a method, a use, or an assembly according to the invention.

[0044] In an embodiment, the panel body of each of the individual panels has a perimeter that is defined by the panel peripheral surface of the panel body. Preferably, the panel peripheral surface is oblique relative to the panel front surface along at least 20 percent of the perimeter, preferably at least 50 percent of the perimeter, more preferably at least 80 percent of the perimeter. In an embodiment, the panel peripheral surface is oblique relative to the panel front surface along at least 20 percent of the panel peripheral surface, preferably at least 50 percent of the panel peripheral surface, more preferably along at least 80 percent of the panel peripheral surface. Optionally, other parts of the panel peripheral surface are at a substantially right angle to the panel front surface.

[0045] In an embodiment, the panel has a rectangular shape, said rectangular shape defining a longitudinal panel direction of the panel. According to an option, a part of the panel peripheral surface that extends along the longitudinal panel direction is oblique relative to the panel front surface, while a part of the panel peripheral surface that extends transverse to the longitudinal panel direction is at a substantially right angle relative to the panel front surface. According to another option, a part of the panel peripheral surface that extends in a direction that is transverse to the longitudinal panel direction is oblique relative to the panel front surfaces, while a part of the panel peripheral surface that extends along the longitudinal panel direction is at a substantially right angle relative to the panel front surface.

[0046] The invention also provides an assembly of a plurality of panels and a wall of a building, wherein the plurality of panels covers at least part of the wall of the building, wherein individual panels of said plurality of panels each include a panel body and have a panel front surface, a panel back surface, and a panel peripheral surface, wherein the plurality of panels is positioned along the wall so that the panel front surfaces face away from the wall, wherein the panel bodies of the plurality of panels are spaced apart from each other so that the plurality of panels has a peripheral gap between the panel bodies, and wherein the panel back surfaces of the plurality of panels are at least partly spaced apart from the wall so that the assembly defines a wall gap between the panel bodies and the wall. According to an aspect, the plurality of panels is arranged and positioned for realising, in the wall gap and / or the peripheral gap, absorption of low-frequency acoustic noise that is generated outside of the building and that propagated towards the wall to reach the wall gap and / or the peripheral gap. According to a further aspect, the plurality of panels is arranged and positioned for reducing reflection in a direction away from the wall of the building and / or reducing transmission into the wall of the building, of low-frequency acoustic noise that is generated outside of the building and that propagated towards the wall to reach the wall gap and / or the peripheral gap.

[0047] Preferably, the assembly is used in a method according to the invention and / or in a use according to the invention. Preferably, the assembly includes one or more panels according to the invention. Optionally, each of the individual panels is a panel according to the invention.

[0048] As described above, the present disclosure relates to a method, a use, a panel, and an assembly. Any feature, example, variation, or embodiment disclosed herein in relation to at least one of said method, use, panel, and assembly, may also be applied in relation to the other ones of the method, use, panel, and assembly.BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The invention will be illustrated with reference to the following non-limiting figures, wherein: Figures 1A-1D shows different examples of a plurality of panels that cover at least part of a wall of a building; Figure 2A schematically shows the plurality of panels in a cross section indicated in figure 1A; Figure 2B schematically shows the plurality of individual panels in a cross similar crosse section similar to the one in figure 2A, however in another embodiment; Figures 3A-3I schematically show, in a back side view, different examples of an individual panel having an oblique panel peripheral surface or an oblique part of the panel peripheral surface; Figure 4 shows a detail indicated in figure 2A; Figure 5A shows absorption coefficients α S that are determined based on measurements in a reverberation room, in five different experiments; Figure 5B shows absorption coefficients α S that are determined in three different numerical simulations; Figure 6A schematically shows a transparent top view of a panelling design that was used in the experiments; Figure 6B schematically shows a transparent top view of another panelling design that was used in the experiments; Figure 6C shows a cross section indicated in figure 6A; Figure 7A shows a plurality of panels in a back side view, when being positioned along a vertical wall; Figure 7B shows the plurality of panels of figure 7A in a top view of a horizontal cross section through the vertical wall, when being positioned along the vertical wall; and Figure 8 schematically shows, in a top view, a plurality of buildings, each at least partly covered by means of a plurality of panels. DETAILED DESCRIPTION

[0050] The present disclosure relates to a method of covering at least part of a wall of a building by means of a plurality of panels, directed to the purpose of absorbing low-frequency acoustic noise. Such noise may e.g. be generated in, or may propagate into, an environment of the building and propagate towards the wall. The panels may be of various shape and composition. For example, the panels may each have a panel body that is made of fibre cement material, or at least includes 50 weight percent fibre cement material. Fibre cement material is a material that includes cement and fibers, and that thus may be regarded as a composite material. The fibers may be cellulose fibers and / or synthetic fibers. The manufacture of fibre cement material is known as such. Panels with another composition may be used alternatively or additionally to panels that include a fibre cement material. Preferably, the body of the panels includes a porous material. The porous material may e.g. have a porosity in a range from 10 percent to 40 percent, preferably in a range from 14 percent to 24 percent. The porosity may, at least partly, be connected. Optionally, the porous material is permeable.

[0051] The use of a plurality of panels for covering a wall of a building for decorative purposes is known as such. Architects or other designers have designed individual buildings that are provided with such panels. For such decorative purposes, panels having a body that is made of a fibre cement material are also used. Against the background of such use of panels for decorative purposes, it was surprisingly found that the plurality of panels can also be used for absorbing low-frequency acoustic noise. Although some types of decorative panels may be not, or may be less, suitable for the purpose of absorbing low-frequency acoustic noise, other decorative panels may be used in a method, a use and / or an assembly according to the present disclosure. Additionally or alternatively to known decorative panels, other panels may be used. A panel thickness of the panels, and / or a thickness of bodies of the panels, may be in a range from 6 millimetres to 15 millimetres, in particular may be about 8 millimetres or about 12 millimetres. The panels and / or the panel bodies may for example have a width in a range from 0,3 metre to 2 metres, for example about 1 metre or about 1,2 metre, and / or may have a length in a range from about 1 metre to about 4 metres, for example about 1 metre, about 2 metres, or about 3 metres. However, optionally, panels and / or panel bodies that have another width, have another length, and / or have another thickness, may also be suitable.

[0052] The plurality of panels used in a method, use or assembly according to the present disclosure, may be part of a cladding system that further includes a frame. Along the wall of the building, the cladding system may form a facade that extends along the wall and that includes the panels as an outer surface. The panels of the cladding system may be fastened onto the frame of the cladding system. The frame may be fixed or otherwise attached to the wall, or to another support structure which is attached to the wall. A wall gap that e.g. can be used for ventilation may be present behind the panels. In addition, there may be a space (or, in other words, a peripheral gap) provided in between the panels. The wall gap and open parts of said space may be useful for regulating humidity and temperature of the panels and allow for some temperature-induced expansion (or, in other words, dilatation) of the panels. A gap, closed or open, between panels may even be mandatory to allow for the dilatation of the panels. Often the peripheral gap is closed with a closing element. The closing element may be applied from the back surface or from the front surface of the panel, to obtain protection against intrusion of water and wind. Such closing elements are known as such to the skilled person.

[0053] The present disclosure is directed i.a. to the use of a plurality of panels as a facade with open or partly open joints (or, in other words, an open or partly open gap) in between adjacent panels, for the purpose of realising absorption of low-frequency acoustic noise. Moreover, for this purpose, additional features to the positioning and arrangement of the panels can be introduced, as will be described herein. Experiments and numerical simulations that were carried out, surprisingly show that a significant reduction of low-frequency acoustic noise may be achieved by choosing panel dimensions and open gap dimensions directed to this purpose. Surprisingly, significant effects were found in experiments wherein an aperture ratio of an engineering model that resembled a facade that includes the plurality of panels, was within a range from approximately 0,002 to approximately 0,007. It thus was found that acoustic noise can be reduced significantly in the low-frequency range, in particular around 60 to 70 Hertz. For example, a significant effect was found in a range from 50 Hertz to 100 Hertz, in particular in a range from 50 Hertz to 70 Hertz. Typically, in such ranges, low-frequency acoustic noise generated by aircrafts can be relatively strong and low-frequency acoustic noise generated by road traffic, such as cars and trucks, can also be considerable.

[0054] Low-frequency acoustic noise may be defined as having a frequency that is at most 100 Hertz and optionally at least 20 Hertz. Low-frequency acoustic noise can originate from different sources, including traffic of for example cars, trucks, trains, or airplanes. Another source can be wind energy turbines. Low-frequency acoustic noise may be generated together with acoustic noise having higher frequencies. In view of low-frequency acoustic noise that nowadays is recognized as being problematic or detrimental, possibilities for realising absorption, or for reducing the reflection from a building and / or the transmission into a building, of low-frequency acoustic noise may be appreciated.

[0055] The experimental and numerical results indicate that, by means of the plurality of panels covering at least part of the wall of a building, in practical situations significant absorption of low-frequency acoustic noise can be realised. Such low-frequency acoustic noise may be generated outside of the building and may have propagated towards the wall. The low-frequency acoustic noise is absorbed in the peripheral gap formed by the space between the panels and / or in the wall gap formed by a space between the wall and panel back sides of the plurality of panels. The results of the experiments and of the numerical simulations indicate that such absorption can be optimized by choosing, among other parameters, a planar panel dimension of the panels and dimensions of the peripheral gap between the panels. Said planar panel dimension may be defined as a, preferably shortest, distance from a central part of the panel body to a position on the panel peripheral surface where the peripheral gap is open. For example, for a rectangular panel the planar panel dimension may half a width the panel or half a length of the panel.

[0056] Often, an open peripheral gap between panels is prevented. This may be for aesthetic reasons (for example because a closed peripheral gap contributes to hiding the frame from view), but also in order to prevent rain and wind to enter the wall gap. The peripheral gap may be closed e.g. by means of tape or by means of a T-shaped closing element that can be pushed between the panels. Other manners of closing the peripheral gap can also be used. When large areas are covered, leaving some parts of the peripheral gap open could be beneficial for ventilation of the wall gap, also in view of regulating temperature and humidity. Leaving open significant parts of the peripheral gap however, for example more than 50 percent or more than 80 percent of the peripheral gap, goes against a common preference for closing at least most of the peripheral gap between the panels. Such preference may for example be based on the aim to prevent wind, rain, sand, or rubbish that can be lifted by the wind, to enter the wall gap.

[0057] According to the present disclosure, the peripheral gap may be in fluid communication with (or, in other words, may be fluidly connected to) the wall gap between a body of the panels and the wall. As a result, air can move from the peripheral gap into the wall gap and from the wall gap into the peripheral gap, as a result of propagation of low-frequency acoustic noise. Thus, the low-frequency acoustic noise can propagate through air, from the peripheral gap into the wall gap and vice versa. The wall gap and the peripheral gap may preferably be dimensioned, relative to dimensions of the panels itself, so that low-frequency acoustic noise that propagated through the peripheral gap into the wall gap at least partly cancels out low-frequency acoustic noise that propagated through the central part of the panel body into the wall gap. Such cancelling out may, partly or completely, be the result of destructive interference of low-frequency acoustic noise in the wall gap and / or the peripheral gap. Alternatively, or additionally, the wall gap and the peripheral gap may be dimensioned, relative to dimensions of the panels itself, so that low-frequency acoustic noise that propagated, through the peripheral gap and / or through the central part of the panel body, into the wall gap, is at least partly dissipated. Such dissipation may in particular take place in the peripheral gap. Although such mechanisms can be considered for explaining the experimental results, they are not intended as being limiting to the present disclosure.

[0058] The present disclosure moreover recognises that, in order to combine an effective absorption of low-frequency acoustic noise with one or more other desired properties of the peripheral gap (such as aesthetic properties), it may be advantageous to have a panel peripheral surface that is, partly or completely, oblique relative to the panel front surface. In an embodiment, at least part of the panel peripheral surface of at least one, preferably of each, of the individual panels of the plurality of panels is oblique relative to the panel front surface. Preferably, an angle between the panel peripheral surface and the panel front surface is in a range from 20 degrees to 70 degrees.

[0059] It may thus be clear that panels that are intended for covering at least part of a wall of a building for decorative purposes, but also other panels, can be used for the purpose of absorbing low-frequency acoustic noise that is generated outside of the building and that propagated towards the wall. Such use of panels may be beneficial to the health of people that are in an environment of the building, and possibly live or work in or around said building. The panels may be adapted or optimized for reducing an amount of low-frequency acoustic noise, e.g. by optimizing their composition, porosity, shape, size, and positioning relative to each other. As a result of the absorption, it moreover can be expected that the panels can be used for reducing the reflection in a direction away from the wall of the building and / or for reducing a transmission into the wall of the building, of low-frequency acoustic noise that is generated outside of the building and that propagated towards the wall. Without wanting to be bound by theory, said reducing of the reflection and / or the transmission may originate from a loss of acoustic energy as a result of the absorption. The absorption may cause less acoustic energy to be available for the reflection and / or the transmission.

[0060] In this way, a less noisy environment may be realised (or in other words, achieved) in an environment of the building. The environment may e.g. be within a substantially horizontal distance of 100 metres from the building, or within a substantially horizontal distance of 300 or 500 metres from the building. In addition, less low-frequency acoustic noise may possibly be present also inside the building. For example, the less noisy environment may diminish an amount of low-frequency acoustic noise to reflect back to the building. Such reductions in low-frequency acoustic noise may be appreciated in particular when the building is next to a motorway (e.g. is within 100, 300, or 500 metres of a motorway) while the wall faces the motorway. A less noisy environment may also be appreciated if the wall faces a garden of a house that experiences low-frequency acoustic noise, e.g. generated by traffic on a motorway of by airplanes. Realising a less noisy environment by means of the plurality of panels may be even more effective if applied to several buildings that face each other and preferably are in an environment of each other. For a peripheral gap having, along at least part of the peripheral gap, a width that increases along a direction through the peripheral gap towards the wall, the plurality of panels may be relatively effective in absorption of low-frequency acoustic noise while at the panel front surface the peripheral gap width can be limited.

[0061] Figures 1A-1D show different examples of a plurality of panels 2 that cover at least part of a wall of a building. The wall is not indicated in figures 1A-1D, but examples of the wall are indicated in figures 2A, 2B, 4, 7B, and 8 with reference number 4, 4.1, or 4.2. Individual panels 2 of the plurality of panels may have the form of a polygon with three or four corners, examples of which are shown in figures 1A-1D. The individual panels 2 may e.g. have a rectangular shape, as shown in figures 1A-1C. Alternatively, or additionally, the individual panels 2 of the plurality of panels may have a similar size and shape, an example of which is illustrated in figure 1A. Alternatively, a number of the individual panels 2 may have a shape and / or size that differs from other ones of the individual panels 2, as shown in figures 1B-1D. Individual panels 2 that are similar and / or have a rectangular shape may provide the advantage of being more easy to position along the wall. It however may be clear from figures 1A-1D that the plurality of panels 2 used for covering the at least part of the wall may be selected from many different shapes and sizes. A width M (indicated in figures 2A and 2B) of the panels may for example be about 1220 millimetre. A panel length, measured in a direction that is perpendicular to the direction in which the width M is measured, may for example be about 2500 millimetre or about 3050 millimetres.

[0062] Figure 2A schematically shows the plurality of individual panels 2 in a cross section A-A' indicated in figure 1A. Figure 2B schematically shows a plurality of individual panels 2 in a cross section similar to the one in figure 2A, however in another embodiment. Figure 4 shows a detail B indicated in figure 2A. The individual panels 2 cover at least part of the wall 4. The individual panels 2 each include a panel body 6. Each of the individual panels also has a panel front surface 8, a panel back surface 10, and a panel peripheral surface 12. The panel front surface 8, the panel back surface 10 and / or the panel peripheral surface 12, or a part thereof, may be formed by a surface layer or other finishing that is provided on the panel body 6 and that is different from the panel body. The finishing may e.g. be paint. Alternatively, or additionally, the panel front surface 8, the panel back surface 10 and / or the panel peripheral surface 12, or a part thereof, may be formed by an outer surface of the panel body itself. For example, the panel body may initially be positioned without any finishing and could be painted only after being positioned along the wall.

[0063] Two methods according to two different embodiments of the invention are illustrated with reference to figure 2A respectively figure 2B. The methods include covering at least part of the wall 4 of a building by means of the plurality of panels 2. The methods further include positioning the plurality of panels 2 so that the panel front surfaces 8 face away from the wall. After the positioning, the panel bodies 6 of said plurality of panels are spaced apart from each other for having a peripheral gap 14 between the panel bodies 6, as illustrated for example in figures 1A-1D, 2A, 2B, and 4. More in general, the peripheral gap may be shaped as a lattice that extends in between the panels. The lattice may for example have regular and rectangular lattice elements (such as in figure 1A), may have irregular and rectangular lattice elements (such as in figures 1B and 1C), and / or may have other irregular lattice elements (such as in figure 1D). After the positioning, the panel back surfaces 10 of the panels 2 are at least partly spaced apart from the wall 4 for having a wall gap 16 between the panel bodies 6 and the wall 4. As illustrated in figures 1A-1D, the plurality of panels 2 may form a group of panels. Each panel of the group of panels may be neighbouring to at least one other panel of the group of panels. Each panel of the group of panels may be separated from at least one other panel of the group of panels only by the peripheral gap 14.

[0064] The positioning of the plurality of panels along the wall may include attaching the plurality of panels to a frame. This may be done by conventional ways of attaching, such as attaching by means of screws. The positioning of the plurality of panels along the wall may further include attaching the frame to the wall. This may also be done by means of conventional ways of attaching, such as attaching by means of bolts. The frame may e.g. include aluminium and / or wood. Normally, the frame is positioned at least partly in the wall gap 16. In some variations, the frame may also fill part of the peripheral gap 14. In some embodiments, a width W of the wall gap 16 (indicated in figures 2A and 2B and also identifiable in figures 4, 6C, 7B and 8) may for example be at least 100 millimetres and / or may be at most 300 millimetres, for example may be about 200 millimetres.

[0065] Figures 1A-1D indicate that the peripheral gap 14 may surround, partly or completely, the panel bodies 6 of the plurality of panels 2. Thus, the peripheral gap may extend along at least part of a perimeter (indicated with reference number 20 in figure 1A) of the panel bodies 6. The peripheral gap is open or is partly open. In an open peripheral gap, and in open parts of the peripheral gap, the peripheral gap is filled with air while air can freely move through the peripheral gap towards the wall gap and vice versa. Preferably, the peripheral gap is open along the perimeter of the bodies 6 of the individual panels 2. The perimeter 20 may be defined by the panel peripheral surface 12 of the panel body. As indicated in figures 1A and 1D, the peripheral gap 14 extends in a longitudinal peripheral gap direction 13 in between at least two panel bodies 6 of said plurality of panels 2. The peripheral gap, as indicated in figures 2A and 2B, has a width N in a direction that is transverse, e.g. perpendicular, to said longitudinal peripheral gap direction 13 and that is along, e.g. perpendicular with, the panel front surfaces 8 of the at least two panels 2. In the embodiment illustrated with reference to figure 2A, the width N shown is substantially constant along the propagation direction 18 of the low-frequency acoustic noise through the peripheral gap 14 towards the wall 4. In the embodiment illustrated with reference to figure 2B however, the width shown increases along said propagation direction 18.

[0066] As illustrated in the embodiment of figure 2B, the panel peripheral surfaces 12 of the individual panels 2 may be oblique relative to the panel front surfaces 8 of the individual panels. Along at least part of the peripheral gap 14, the width N of the peripheral gap 14 may increase along a direction 19 through the peripheral gap towards the wall 4. The width N of the peripheral gap may increase along the direction 19 through the peripheral gap towards the wall, along at least 20 percent, at least 50 percent, or at least 80 percent of the peripheral gap 14. An angle β between the panel peripheral surface and the panel front surface 8 may be in a range from 20 degrees to 70 degrees, preferably in a range from 30 degrees to 60 degrees, for example approximately 45 degrees. If the angle is too large (i.e. too close to 90 degrees), an effect of the angle will be relatively small. If the angle is too small, the panel may become relatively thin and vulnerable. The obliqueness as described herein may enable the peripheral gap to appear closed, or almost closed, to an observer looking to the front surfaces of the plurality of panels, for example because at the panel front surface the peripheral gap width is at most 4 millimetre or at most 6 millimetres. As indicated in figure 2B, at the panel front surface 8 the peripheral gap width N may have its smallest value. At the same time, the obliqueness may enable the peripheral gap 14 to be still effective for absorbing low-frequency acoustic noise.

[0067] Oblique panel peripheral surfaces may be applied along at least part of the peripheral gap, and optionally along substantially the whole peripheral gap. Oblique panel peripheral surfaces may be applied at open parts of the peripheral gap. As will later be illustrated with reference to figure 5B, such an angle may increase the absorption of low-frequency acoustic waves. Hence, by means of a panel peripheral surface with such an angle, the plurality of panels 2 may better absorb low-frequency acoustic noise that is generated outside of the building and that propagated towards the wall. As shown in figure 5B, such an effect may in particular be achieved when the peripheral gap width N at the front surface is in a range from 6 millimetres to 14 millimetres, and in particular is about 8 millimetres. An oblique peripheral gap may also be beneficial in view of regulations on the peripheral gap width at the panel front surface, which may limit in practice the peripheral gap width that can be applied. Along parts of the peripheral gap where the peripheral gap is closed, the peripheral gap may be at a substantially right angle to the panel front surface. Such a right angle may facilitate the closing of the peripheral gap.

[0068] For example, in the example of figures 1B and 1C, the plurality of panels each have a rectangular shape that defines a longitudinal panel direction of the panels. The longitudinal panel direction is in a horizontal direction in figure 1B, and is in a vertical direction in figure 1C. In the example of figure 1B, the parts of the panel peripheral surfaces that extend in the longitudinal panel direction may be partly or completely oblique, while the parts of the panel peripheral surfaces that extend transverse to the longitudinal panel direction may be at a substantially right angle to the panel front surface. In the example of figure 1C, the parts of the panel peripheral surfaces that extend in a direction that is transverse to the longitudinal panel direction may be partly or completely oblique, while the panel peripheral surfaces that extend in the longitudinal panel direction may be at a substantially right angle to the panel front surface. As a result, in both figures 1B and 1C, horizontal parts of the panel peripheral gap may be open or partly open and may be provided with an at least partly oblique panel peripheral surface, while vertical parts of the panel peripheral gap may be closed.

[0069] Figures 3A-3I each schematically illustrate different examples of an individual panel 2. Each of the panels 2 of figures 3A-3I may be one of a plurality of panels that can be used in a method, use, or assembly according to the present disclosure. The individual panels of said plurality may be similar to each other. Thus, the features of a panel 2 shown in one of figures 3A-3I, may also be implemented in a majority of, or in each of, the other panels of the plurality of panels. The plurality of panels can be used in a method, a use, or an assembly according to the present disclosure. A transition 15 from the panel back surface 10 to the panel peripheral surface 12 is schematically indicated in figures 3A-3I as well. In figure 3C, the whole of the panel peripheral surface 12 is oblique relative to the panel front surface (not visible in figures 3A-3I). In the other ones of figures 3A-3I, part of the panel peripheral surface 12 is oblique relative to the panel front surface. Other parts of the panel peripheral surface 12 may be at a substantially right angle to the panel front surface.

[0070] In the present disclosure, a substantially right angle may refer to an angle within the range from 70 degrees to 110 degrees, preferably to an angle within the range from 80 degrees to 100 degrees. Hence, a substantially right angle may deviate plus or minus 10 degrees, or plus or minus 20 degrees, from a right angle of 90 degrees. In case the panel front surface includes irregularities, such as for example channels in the panel front surface, the panel front surface can be considered to coincide with the top parts of the panel front surface. The panel front surface may e.g. be defined such that it is planar and that all of the panel body is behind the panel front surface. Along the oblique panel peripheral surface 12, and / or along the oblique part of the panel peripheral surface 12, an angle β (illustrated in figure 2B) between the panel peripheral surface 12 and the panel front surface may be in a range from 20 degrees to 70 degrees.

[0071] As indicated in figures 3A-3I, the panel 2 may have a substantially rectangular shape. The rectangular shape may define a longitudinal panel direction 17 of the panel 2. A part of the panel peripheral surface 12 that extends along the longitudinal panel direction 17 may be oblique relative to the panel front surface. This can be seen e.g. in figures 3A, 3C, 3D, 3F, 3H, and 3I. In all of figures 3A-3I except figures 3B and 3C, a part of the panel peripheral surface that extends transverse to the longitudinal panel direction 17 is at a substantially right angle relative to the panel front surface. A part of the panel peripheral surface 12 that extends in a direction that is transverse to the longitudinal panel direction 17, may at least partly be oblique relative to the panel front surface. Examples of this feature can be seen in figures 3B, 3C, 3E, 3F, and 3G. In all of figures 3A-3I except figures 3A and 3C, a part of the panel peripheral surface that extends along the longitudinal panel direction is at a substantially right angle relative to the panel front surface.

[0072] In an embodiment, at least 20 percent of the panel peripheral surface is oblique relative to the panel front surface or at least 50 percent of the panel peripheral surface is oblique relative to the panel front surface. The latter feature is implemented in figures 3A, 3C, and 3D. In for example figure 3C, at least 80 percent of the panel peripheral surface is oblique relative to the panel front surface. Parts of the panel peripheral surface 12 that are not visible in the back side view of figures 3A-3I, may be at a substantially right angle to the panel front surface. In an embodiment, at least a part of the panel peripheral surface 12 that extends along the longitudinal panel direction 17 and at least a part of the panel peripheral surface 12 that extends transverse to the longitudinal panel direction 17, are oblique relative to the panel front surface. Examples of this feature are visible in figures 3C and 3F. In an embodiment, parts of the panel peripheral surface 12 that are located opposite to each other and / or are at opposite sides of the panel body, are oblique relative to the panel front surface. Examples of this feature are visible in figures 3A, 3B, 3C, 3D, 3E, 3H, and 3I. In an embodiment, a part of the panel peripheral surface 12 that extends along the longitudinal panel direction 17 and a part of the panel peripheral surface 12 that extends in a direction transverse to the longitudinal panel direction, both are oblique relative to the panel front surface. Examples of this feature are visible in figures 3C and 3F. In an embodiment, a part of the panel peripheral surface 12 that is oblique relative to the panel front surface extends either along or transverse to the longitudinal panel direction. Examples of this feature are visible in all of figures 3A-3I except figures 3C and 3F.

[0073] The panels of figures 3A and 3B may be preferred, in view of ease of manufacturing. Additionally, or alternatively, the panels of figures 3A and 3B may be preferred in view of enabling a peripheral gap in between peripheral side surfaces that are at substantially right angles to the panel front surfaces in one direction and a peripheral gap between peripheral side surfaces that are oblique relatively to the panel front surfaces in another direction that is transverse to said one direction. As illustrated in figures 3A-3I, the panel bodies of the plurality of panels may each have four corners. As shown in figures 3D-3I, the panel peripheral surface of the individual panels may be, relative to the panel front surface, oblique along part of the panel peripheral surface and at a substantially right angle at the corners of the panel peripheral surface. As shown in figure 3G, in between one pair of neighbouring corners the panel peripheral surface may be partly oblique relative to the panel front surface. As shown in each of figures 3D, 3E, 3F, 3H, and 3I, in between two pairs of neighbouring corners the panel peripheral surface may be partly oblique relative to the panel front surface. Corners may be considered to be neighbouring if, along the panel peripheral surface, no other corner is in between the neighbouring corners.

[0074] One or more of the individual panels described with reference to figures 3A-3I, or the mirror images thereof, may be applied in a method, a use, a panel or an assembly disclosed herein. The individuals panels described with reference to figures 3A-3I, and the mirror images thereof, may each be applied in the orientation shown, or in a rotated orientation. For example, when covering at least part of a wall, the individual panels of one or more of figures 3A-3I, and / or a mirror image thereof, may be rotated 90 degrees relative to the orientation shown in figures 3A-3I. In the embodiments of figure 2A and 2B, the method includes, by means of the plurality of panels 2, realising absorption of low-frequency acoustic noise. Such low-frequency acoustic noise may be generated outside of the building and may have propagated towards the wall 4. The acoustic noise is schematically indicated in figures 2A, 2B, and 4 by means of arrows 18. The low-frequency acoustic noise may propagate towards and into the wall gap via two different paths. As indicated in figure 4, a first path towards and into the wall gap 16 is through the panel body 6, indicated in figure 4 by straight arrows 18. A second path towards and into the wall gap is through the peripheral gap, indicated in figure 4 through curved arrows 18.

[0075] Figure 4 illustrates that parts of a wave of low-frequency acoustic noise that propagates towards and into the wall gap via the panel body (along the first path), will show a phase difference at a position in the wall gap compared to another part of said wave of low-frequency acoustic noise that reaches said position in the wall gap 16 via the peripheral gap (along the second path). Said phase difference may be relatively large for low-frequency acoustic noise that propagates through a central part 22 of the panel body 6 towards and into the wall gap 16. Said phase difference may be relatively small for low-frequency acoustic noise that propagates through an edge part 24 of the panel body 6 towards into the wall gap 16.

[0076] Without intending to be bound by theory, cancellation of low-frequency acoustic noise may be achieved that reaches the wall gap via different paths. Alternatively, or additionally, the low-frequency acoustic noise 18 that propagated, through the peripheral gap 14 and / or through the panel body 6, into the wall gap 16, may at least partly be dissipated. Such dissipation may in particular take place in the peripheral gap. All together, the absorption may be understood to result from a complex interaction between low-frequency acoustic waves in the wall gap and / or in the peripheral gap, whose effects are difficult to predict in advance. It may be clear however, that a peripheral gap that is at least partly open is beneficial for realising the absorption, while it can be considered counter-intuitive to leave open at least part of the peripheral gap when covering the at least part of the wall.

[0077] Figures 5A and 5B show results of an absorption spectrum obtained in five experiments respectively of three numerical simulations. Figures 5A and 5B show, along the vertical axis, the absorption coefficient α S of a plurality of panels that cover a part of a floor wall. The absorption coefficient α S is shown as a function of frequency F (measured in Hertz), which is along the horizontal axis in figures 5A and 5B. In the experiments of figure 5A, the absorption coefficient is determined in a reverberation room as a function of frequency, using different panelling designs. In the experiments, a plurality of panels is positioned along part of a bottom wall of the reverberation room. The plurality of panels thus cover a part of the bottom wall of the reverberation room. The absorption coefficient α S can be determined by measuring an acoustic response in the reverberation room with the panels covering part of the bottom wall, relative to the acoustic response in the reverberation room without the panels being positioned therein. In the experiments of Fig. 5B, the absorption coefficient is determined by means of numerical simulation.

[0078] Methods for determining the absorption coefficient are known as such to the skilled person. Preferably, the method based on ISO standard NF EN ISO 354 (2004) is used, optionally in combination with ISO standard 9613-1:1993(EN). The methods described in said standards are known as such to the skilled person and are based on generally known and accepted methods. According to the first of said standards, the absorption coefficient α S is determined by calculating an equivalent absorption area A T and dividing it by the frontal surface area of the engineering model. The equivalent absorption area A T depends on the reverberation time T 1 and the sound velocity c 1 in an empty room, and on the reverberation time T 2 and the velocity of sound c 2 in a room with a plurality of panels covering part of the floor of the reverberation room. The reverberation time may be defined as the time that would be required for a measured sound pressure level to decrease by 60 dB after the sound source that is used for generating sound for the measurements in the reverberation room has stopped. The equivalent absorption area A T also depends on the volume V of the reverberation room. The dependency of the equivalent absorption area A T on said variables is determined by: A T = 55,3 V 1 c 2 T 2 − 1 c 1 T 1 − 4 V m 2 − m 1 wherein the following temperature-dependency of the sound velocity c on temperature is used: c = 331 + 0,6 t , wherein t indicates temperature in degrees Celsius at the moment of measuring and should be in between 15 degrees Celsius and 30 degrees Celsius. The absorption coefficient α S equals the equivalent absorption area A T divided by the frontal surface area. The equivalent absorption area A T and the absorption coefficient α S may be determined for frequencies that subsequently increase with one-third of an octave.

[0079] If, in the reverberation room, the air temperature, ambient atmospheric pressure, and / or concentration of water vapour in the air during the measurement in the empty reverberation room differ from respectively the air temperature, ambient atmospheric pressure and / or concentration of water vapour in the air during the measurement in the reverberation room with a plurality of panels covering part the floor wall of the reverberation room, a correction can be applied to the equivalent absorption area A T . As expressed in the above formula, the correction equals -4V(m 2 - m 1 ), wherein m 1 and m 2 are the attenuation coefficients during measuring of the reverberation time in the empty room respectively in the room wherein the plurality of panels covers part of the floor of the reverberation room. The correction can be relatively small. The values of m 1 and m 2 can be inferred from the ISO standard 9613-1 : 1993(EN). However, preferably, the temperature, ambient atmospheric pressure and concentration of water vapour are the same during both measurements, so that the attenuation coefficients m 1 and m 2 are about the same and the correction is negligible.

[0080] The absorption coefficient α S that is determined in the experiments in the reverberation room in this way, can be considered to be indicative for absorption of low-frequency acoustic energy in practical situations. Hence, the absorption properties of a plurality of panels as described in the present disclosure, may be determined in a reverberation room according to standardised methods such as ISO standard NF EN ISO 354 (2004) and optionally ISO standard 9613-1 : 1993(EN), as described herein. For such determinations, engineering models can be used that resemble the practical situation. Preferably, in an engineering model, panels of a similar type, composition, and dimensions are used as in the practical situation that is to be assessed. Preferably, in an engineering model, a similar peripheral gap and wall gap is used as in the practical situation that is to be assessed. An engineering model may e.g. resemble, or be similar to, at least a part of a facade that includes a plurality of panels and that is to be assessed.

[0081] Figure 5A shows results of five experiments labelled E1, E2, E3, E4, and E5. In each of the experiments, a different type of panel or panelling design is tested. Panels of a first type, which are marketed under the trade name Equitone@ Picture, were used in experiment E1. The panels of this first type have a panel thickness Y of 8 millimetre and weigh 15,6 kilogram per square metre. Panels of the first type have a planar front surface that is formed by a UV-cured coating. Panels of a second type, which are marketed under the name Equitone ®< Linea, were used in experiment E2. Panels of this second type have a thickness that varies between 8 and 10 millimetre and weigh 16,3 kilogram per square metre. The panels of the second type are uncoated, so that the panel front surface is formed by the panel body. The variation in thickness of the panels of the second type is caused by a structure of straight and parallel channels in the panel front surface with a depth of about 2 millimetre that extend along the panel front surface at a regular distance from each other.

[0082] Panels of a third type, which are marketed under the name Equitone@ Lunara, were used in experiment E3. The panels of this third type have a thickness of approximately 10 millimetre and weigh about 18,5 kilogram per square metre. The panels of the third type are uncoated, so that the panel front surface is formed by the panel body. At the panel front surface a quasi-random pattern of surface variations is provided. Panels of a fourth type, which are marketed under the name Equitone@ Tectiva, were used in experiment E4 and E5. Panels of the fourth type have a thickness of about 8 millimetre and weigh about 14,6 kilogram per square metre (in experiment E4) or about 14,4 kilogram per square metre (in experiment E5). The panels of the fourth type are uncoated, so that the panel front surface is formed by the panel body. The panel front surface of the panels of the fourth type is planar and is sanded.

[0083] The four types of panels that were used in the experiments E1-E5, all have a body made of fibre cement material. They are commercially available and known as such to the skilled person. The panel bodies of these types of panels are porous and may typically have a porosity in a range from about 13 percent to about 25 percent, in particular in a range from about 15 percent to about 22 percent. The Equitone@ Lunara, Linea and Tectiva panels are based on autoclave-cured technology and have essentially corresponding material constitution. These panels are without surface coating. The Equitone@ Picture panel is a coated panel of which the fiber cement material is manufactured in air-cured technology. All Equitone@ panels are commercially available from Eternit NV, Kapelle-op-den-Bos, Belgium.

[0084] Figures 6A and 6B schematically show a transparent top view of the two engineering models 28 with mutually differing panelling designs that were used in the experiments. Figure 6C shows a cross section C-C' indicated in figure 6A. The panelling of figure 6A is provided with nine rectangular individual panels. In the view of figure 6A, these panels have a panel length that extends in the horizontal direction and a panel width that extends in the vertical direction. In the panelling design shown in figure 6A, the panel width is about 989 millimetres and the panel length is about 1189 millimetre. The panelling of figure 6B is provided with six rectangular individual panels 2. In the view of figure 6B, the panels have a panel length that extends in the vertical direction and a panel width that extends in the horizontal direction. In the panelling design shown in figure 6B, the panel width is about 1189 millimetre and the panel length is about 1488 millimetre. In the panelling design of the engineering model of figure 6A, the peripheral gap is about 8 millimetres. In the panelling design of the engineering model of figure 6B, the peripheral gap is about 12 millimetres. An engineering model having the panelling design of figure 6A was used in experiments E1, E2, E3, and E4. An engineering model having the panelling design of figure 6B was used in experiment E5.

[0085] For both panelling designs shown in figures 6A and 6B, an aperture ratio may be defined, for the plurality of panels that form a façade. The aperture ratio of the plurality of panels, i.e. of the facade, may be defined as the ratio of an area, measured along the panel front surfaces, of an open part of the façade and a closed part of the facade. Thus, the aperture ratio may equal the area, measured in a direction along the panel front surface, of the open parts of the façade (formed by the open parts of the peripheral gap at the front surface) divided by the closed area of the facade (formed by the sum of the area of the panel front surfaces and the area of the closed parts of the peripheral gap at the front surfaces). In the panelling design of figures 6A and 6B, the aperture ratio was within a range from 0,002 to 0,007. In a practical embodiment, the facade may have an aperture ratio of at most 0,02, preferably at most 0,01, more preferably at most 0,005.

[0086] In both engineering models 28, below the panels 2, a width W of the wall gap 16 (indicated in figure 2) of 200 millimetre is provided (indicated in figure 6C). A layer of rock wool that can dampen low-frequency acoustic noise, is provided in the wall gap. Thus, part of the wall gap 16 is filled with a layer of rock wool 30, having a thickness of about 150 millimetres. In view of the width of the wall gap, in this embodiment, a majority of the wall gap is filled with rock wool. On top of the layer of rock wool, wooden bars 32 are provided. The wooden bars have a length of about 3000 millimetres, a width of about 145 millimetres and a thickness of about 45 millimetres. The panels 2 are attached to these bars with screws 34. A layer of felt 36 is provided in between the bars 32 and the panels 2. The layer of felt has a width of about 100 millimetres. The wooden bars 32 may resemble the frame with which the panels may be attached to the wall. A frontal surface 33 of the engineering model was 10,8 square metres. The frontal surface may be formed by the panel front surfaces, the peripheral gap (whether closed or open), and an edge formed by a border element 38.

[0087] In the panelling designs shown in figures 6A and 6B, a planar panel dimension P of about 495 millimetres respectively about 744 millimetres can be recognised. This planar panel dimension may be the shortest distance from a central panel body part 22 to a position 42 on the panel peripheral surface where the peripheral gap is open. In this embodiment, and in other embodiments, the central panel body part 22 may e.g. coincide with a midpoint of the panel body 6, in particular with an imaginary axis that extends through said midpoint in a direction perpendicular to the panel front surface. The midpoint may e.g. be formed by the centre of gravity of the panel when the panel front surface is in a substantially horizontal position. In the design of figure 6A, the planar panel dimension P is half of a width of a panel. In the panelling design of figure 6B, the planar panel dimension P is half of a length of a panel. The border element 38 is provided around the panelling, which may be made of a wooden plank. In both designs, the outer dimensions of the panelling design are 3000 millimetres by 3600 millimetres. As will be clear from figures 6A-6C, the parts of the peripheral gap 14 that are vertical in figures 6A and 6B, are blocked (i.e. closed) by means of the bars 32 in combination with the layer of felt 36. At the border element 38, aluminium tape 40 is applied to obtain a sufficient acoustic isolation between the border element 38 and the floor wall 4, and between the border element 38 and the panels 2 along the border element 38. The tape 40 is drawn in figure 6C but is not visible in figures 6A and 6B.

[0088] The absorption coefficient of the engineering panels was determined based on the method according to ISO standard NF EN ISO 354 (2004) and ISO standard 9613-1:1993(EN), which is described herein above. The experiments were carried out in a reverberation room, having walls with relatively hard surfaces that may be formed by concrete. The reverberation room has a volume of 252 cubic metre and is provided with twelve diffusers. It is equipped with sensors for measuring temperature, relative humidity and atmospheric pressure. In all experiments, the atmospheric pressure was 101,4 kilopascal, the temperature was about 19 degrees Celsius in experiments E1 and E5 and about 19,5 degrees Celsius in experiments E2, E3, and E4, and the relative humidity was about 64 percent, 65 percent, 66 percent, 68 percent, and 69 percent in respectively experiments E1, E2, E3, E4, and E5. In the reference experiments with an empty reverberation room, the temperature was about 19 degrees Celsius, the relative humidity was about 60 percent, and the atmospheric pressure was about 101,4 kilopascal.

[0089] Going back to the experimental results of figure 5A, these firstly indicate that a significant absorption of low-frequency acoustic noise can be realised. At a main absorption frequency (or, in other words, a frequency of the low-frequency acoustic noise at which a maximum of the absorption of low-frequency acoustic noise is reached), the absorption coefficient can be reduced at least 20 percent, at least 30 percent, or at least 40 percent. It may be expected that by further optimization of the planar panel dimension, the peripheral gap, and / or the wall gap, possibly in combination with other properties such as surface properties of the panels and / or a porosity of the panel bodies, the absorption may be further improved. Preferably, the absorption coefficient is at least 50 percent or at least 60 percent, at a main absorption frequency of the low-frequency acoustic noise.

[0090] Comparing experiments E4 and E5, which were carried out with panels of one and the same type, indicates how the open peripheral gap can be relevant. In the experiment E4 wherein the panelling design of figure 6A is applied, the total length of open peripheral gap was about twice as large as in the experiment E5, wherein the panelling design of figure 6B was applied. This was the consequence of the ordering of the panels. In experiment E4 open peripheral gaps were present on opposite sides of a single panel. In other words, there was an open peripheral gap both between a first and a second row of panels and between the second row and a third row of panels. In experiment E5, there was merely a first and a second row of panels and hence merely a single open peripheral gap between those rows. The peripheral gap width was also different between experiment E4 and E5. The experimental results indicate that the absorption coefficient α S in experiment E4 can be about twice as large as the absorption coefficient α S in the experiment E5, for frequencies in a range from about 50 Hertz to about 100 Hertz. In view of the difference in absorption between experiments E4 and E5, preferably an aperture ratio of the facade formed by the plurality of panels, is at least 0,003 or is at least 0,004. Preferably, for the individual panels, a minimum distance between open parts of the peripheral gap that are at opposite sides of the panel body, and that can be connected by a straight line that goes through the central part of the panel body, is at most 1,3 metre. For sake of clarity, it is observed that the ordering of the panels was the same in experiments E1 to E3 as in E4.

[0091] Figure 5B shows the absorption coefficient α S of a plurality of panels that cover a wall, as determined in three different numerical simulations S1, S2, and S3. The numerical simulations were carried out using a numerical Transfer Matrix Method. Commercially available software packages are available for carrying out numerical simulations of this type, which is known as such to the skilled person. The numerical simulations take into account, among other variables, the aperture ratio of the engineering models and properties of materials used in the engineering models. Although carrying out the numerical simulations requires making assumptions and approximations, the numerical simulations were found to roughly confirm the experimental results (as visible in figures 5A and 5B).

[0092] In the numerical simulations S1 and S2, a peripheral gap width of 8 millimetre respectively 10 millimetre was implemented. The peripheral gap width was substantially constant along a propagation direction of the low-frequency acoustic noise through the peripheral gap towards the wall. In the numerical simulation S3, a peripheral gap width at the panel front surface of 8 millimetre was implemented. This peripheral gap width increased along the propagation direction of said low-frequency acoustic noise through the peripheral gap towards the wall. An angle β (indicated in figure 4) of 45 degrees was implemented in the model used for the numerical simulation S3. In the numerical simulations S1. S2, and S3, values for the materials properties and dimensions of the layers were used that are representative for the engineering models 28 described with reference to figures 6A-6C.

[0093] The numerical simulations S1 and S2 thus indicate that a wider peripheral gap of 10 millimetres instead of 8 millimetres, increased the absorption. The numerical simulations S1 and S3 indicate that a panel peripheral surface that is oblique (or, in other words, inclined) relative to the panel front surface so that the peripheral gap becomes wider along a propagation direction of the low-frequency acoustic noise through the peripheral gap towards the wall, also increases the absorption. The results of the experiments and numerical simulations indicate, more in general, that a significant absorption of low-frequency acoustic noise may be realised in practice by means of the panels in combination with the peripheral gap and the wall gap. Such absorption could moreover, optionally, lead to a reduction of the transmission of the low-frequency acoustic noise into a building and / or to a significant reduction of the reflection of the low-frequency acoustic noise in a direction away from the wall. After all, as a result of the absorption, less acoustic energy of the low-frequency acoustic noise could be available for such transmission and / or reflection. Figures 5A and 5B show that at a main absorption frequency in the low-frequency range below 100 Hertz, a maximum of the absorption can be reached. Possibly, at a similar frequency, a maximum in the reduction of the reflection and / or transmission can be reached.

[0094] More specifically, the experiments and numerical simulations that are presented with reference to figures 5A-6C, illustrate that the planar panel dimension P, the peripheral gap 14 and the wall gap 16 can be arranged so that a significant amount of absorption of low-frequency acoustic noise can be reached at or around a main absorption frequency. In most of the experiments and numerical simulations that were carried out, said main absorption frequency is about 63 Hertz and the absorption at the main absorption frequency is at least about 30 percent. However, in practical situations, the panelling design may be different, so that another main absorption frequency and / or another absorption level may be realised. Preferably, the main absorption frequency is at least 20 Hertz and / or is at most 100 Hertz, more preferably is at least 40 Hertz and / or is at most 90 Hertz. In particular, the main absorption frequency may be in a range from 50 Hertz to 80 Hertz, for example in a range from 60 Hertz to 70 Hertz. The planar panel dimension may optionally be at least 20 Hertz metre divided by said main absorption frequency and / or may optionally be at most 160 Hertz metre divided by said main absorption frequency.

[0095] Figures 7A and 7B schematically show a plurality of panels that may be used in a method according to one or more embodiments discussed with reference to figures 1A-6C. Figure 7A shows the panels 2 in a back side view, when being positioned along a vertical wall (the vertical wall is not drawn in figure 7A). Figure 7B shows, in a top view of a horizontal cross section through the vertical wall 4, the plurality of panels 2 in an assembly with the vertical wall 4 when being positioned along the wall. The plurality of panels 2 shown in figures 7A and 7B may also be used in other embodiments of the invention. As shown in figures 7A and 7B, the panel back surfaces 10 of the plurality of panels 2 may be provided with a ridge 44. The positioning of the plurality of panels along the wall, may include positioning the ridges 44 against the wall. Each ridge 44 partitions, alone or in combination with other ridges, the wall gap 16 in order to create at least two cavities 46.1, 46.2 in the wall gap that are in fluid communication with the peripheral gap 14. As a result, the low-frequency acoustic noise can propagate through the peripheral gap 14 into the cavity 46.1 or the cavity 46.2 in the wall gap.

[0096] As indicated in figures 7A and 7B, the at least two cavities may have volumes that differ from each other. As a result, acoustic properties of one of the at least two cavities can be different from acoustic properties of another one of the at least two cavities. In particular, a resonance frequency of one of the at least two cavities can be different from a resonance frequency of another one of the at least two cavities. By means of the ridge 44, the absorption of low-frequency acoustic noise by means of the panels 2 may be further adjusted. In particular, the ridge may enable a more even spectrum of the absorption coefficient α S , at least at frequencies in between 20 Hertz and 100 Hertz. In the embodiment of figures 7A and 7B, the ridge is substantially straight. However, in other embodiments the ridge may be curved and / or may have one or more branches.

[0097] The ridges 44 may be formed by a frame that is attached to the wall and to which the plurality of panels is attached. Thus, in an embodiment, the frame may be designed for partitioning the wall gap for forming a plurality of cavities 46.1, 46.2. In another embodiment, the ridges may be integral to the panels. For example, the ridges may be attached to the panels before the panels are attached to the frame and / or to the wall. In another embodiment, part of the ridges 44 may be integral to the panels and part of the ridges are formed by the frame. In such embodiments, a part of the back surfaces of the plurality of panels may contact the wall and another part of the back surfaces of the plurality of panels may be spaced apart from the wall. More in general, the panel back surfaces of the plurality of panels may be completely or may be partly spaced apart from the wall, for having the wall gap between the panel bodies and the wall.

[0098] Figure 8 illustrates a method in a further embodiment of the invention. Figure 8 schematically shows, in a top view, a plurality of buildings each having a wall that is at least partly covered by means of a plurality of panels 2. The wall 4.1 at least partly covered by a plurality of panels 2 of a building 50.1, faces another wall 4.2 that is at least partly covered by a plurality of panels 2. The other wall 4.2 is part of another building 50.2. As a result of the walls 4.1, 4.2 of the two buildings 50.1, 50.2 facing each other, low-frequency acoustic noise that is reflected from the wall 4.1 can propagate towards said other wall 4.2. Two buildings may be regarded to face each other if a ray of acoustic noise that is reflected with an angle of 45 degrees relative to the panel front surface 8 of a panel on one of the two buildings, can reach the other one of the two buildings without further reflections while propagating along a straight line.

[0099] As illustrated in figure 8, the panel back surfaces 10 of the panels 2 may be spaced apart from the wall 4.1. As a result, the assembly of the wall 4.1 and the plurality of panels 2 that at least partly cover the wall 4.1, may define a wall gap 16 between the panel bodies 6 and the wall 4.1. Figure 8 shows the same for the assembly of the wall 4.2 and the panels 2 that at least partly cover the wall 4.2. Figure 8 also schematically illustrates that panel bodies 6 of the plurality of panels are spaced apart from each other. As a result, the plurality of panels 2 that at least partly cover a wall of one of the buildings, has a peripheral gap 14 between the panel bodies 6. As described herein, by means of the positioning of the panels and the dimensioning of the panels, the wall gap, and the peripheral gap, absorption of low-frequency acoustic noise can be realised. If low-frequency acoustic noise that reflected from the building 50.1 is absorbed by means of a plurality of panels 2 on said other building, reducing the amplitude of the low-frequency acoustic noise in an environment of the building 50.1 may be realised effectively.

[0100] As schematically indicated in figure 8, the planar panel dimension, the peripheral gap and / or the wall gap of the plurality of panels positioned along the wall may be different for different buildings. For example, the planar panel dimension, the peripheral gap and / or the wall gap of the plurality of panels positioned along the wall 4.1 may be different from the planar panel dimension, the peripheral gap and / or the wall gap of the plurality of panels along the other wall 4.2. As a result, a main absorption frequency of the low-frequency acoustic noise at which a maximum in the absorption is realised by means of the panels covering the wall 4.1, may be different from another main absorption frequency of low-frequency acoustic noise at which a maximum in the absorption is realised by means of the panels covering the other wall 4.2. In this way, the low-frequency acoustic noise may be absorbed more evenly along a wider range of frequencies (i.e., the absorption spectrum may be broader).

[0101] In the example of figure 8, the wall 4.1 of the building 50.1 and the other wall 4.2 of the other building 50.2, are at opposite sides of a street 52. The low-frequency acoustic noise may e.g. be generated by traffic that propagates on the street 52. Thus, as along the street 52 a plurality of buildings may be provided, one or more other buildings may be present in an environment of each of the buildings shown. The method may include covering at least a part of a wall that faces the street 52 of each of the provided buildings, using a method according to an embodiment of the invention. As a result, low-frequency acoustic noise that is reflected from the wall of one building of the plurality of buildings can propagate towards the wall of another building of the plurality of buildings. By realising absorption by means of the panels at main absorption frequencies that are different for each of the buildings of the plurality of buildings, low-frequency acoustic noise in an environment of the buildings may be absorbed effectively over a wider frequency range.

[0102] The invention is not limited to the embodiments, variations, examples, aspects, features etc. as described herein. For example, the invention may be applied to low-frequency acoustic noise with a frequency of at most 200 Hertz, and optionally of at least 20 Hertz. Optionally, the main absorption frequency is at least 20 Hertz and / or at most 200 Hertz. In an embodiment, the panel and / or the panel body may have a thickness of at least 12 millimetres. An oblique part of a panel peripheral surface referred to herein is not necessarily oblique over the whole distance from panel front surface to panel back surface. Instead, optionally, an oblique part of a panel peripheral surface may e.g. be rounded near the panel front surface or the panel back surface, or may have a substantially right angle to the panel front surface at positions near the panel front surface. In this way, the panel may be less vulnerable to damage. An oblique part of the panel peripheral surface does not have to be flat. It optionally may contain one or more ridges or may contain a stepped profile.

[0103] The walls referred to herein may fall into a broad range of different wall types. For example, one or more of the walls may be vertical, horizontal, and / or inclined relative to the horizontal direction. One or more of the walls may be continuous or may be discontinuous. One or more of the walls may be provided with one or more openings and / or may include two or more wall parts that may be separate. One or more of the walls may include concrete and / or bricks. Alternatively, or additionally, the one or more of the walls may include wood and / or one or more types of wall board. Similarly, the term building may refer a wide range of building types, such as residential buildings, office buildings, hospital building, and / or factory buildings, but also other build structures that include one or more walls.

[0104] Although in the present disclosure the invention is often described with reference to a method of covering the wall, the invention can also be described as a use of a plurality of panels for covering the wall or as an assembly of a plurality of panels and the wall. The embodiments, examples, and features of said method described herein may also be applied in combination with said use or said assembly, or in combination with an individual panel. For example, a frame for attaching the panels to a support structure that is attached to a wall, may be formed by wooden bars like the wooden bars of the engineering models shown in figures 6A and 6B. In addition, the present disclosure also relates to each individual panel disclosed herein and the mirror image thereof, whether or not described as one of a plurality of panels. Such panels may be used in an orientation shown or described, or in a rotated orientation. Such rotation may e.g. be 90 degrees, so that vertical and horizontal directions of the panels are reversed relative to an orientation as described and / or drawn.

Examples

Embodiment Construction

[0050]The present disclosure relates to a method of covering at least part of a wall of a building by means of a plurality of panels, directed to the purpose of absorbing low-frequency acoustic noise. Such noise may e.g. be generated in, or may propagate into, an environment of the building and propagate towards the wall. The panels may be of various shape and composition. For example, the panels may each have a panel body that is made of fibre cement material, or at least includes 50 weight percent fibre cement material. Fibre cement material is a material that includes cement and fibers, and that thus may be regarded as a composite material. The fibers may be cellulose fibers and / or synthetic fibers. The manufacture of fibre cement material is known as such. Panels with another composition may be used alternatively or additionally to panels that include a fibre cement material. Preferably, the body of the panels includes a porous material. The porous material may e.g. have a poros...

FIELD

[0001] The invention relates to a method of covering at least part of a wall of a building by means of a plurality of panels. The invention also relates to use of a plurality of panels for covering at least part of a wall of a building. The invention further relates to a panel that is arranged for covering at least part of a wall of a building. The invention further relates to an assembly of a plurality of panels and a wall of a building, wherein the plurality of panels covers at least part of the wall of the building.BACKGROUND

[0002] Many urban areas have grown to accommodate large amounts of inhabitants and, in particular during working hours, employees. In many cases their numbers are still growing. At the same time, nowadays, available opportunities for urban areas to expand can be limited, e.g. as a result of protection of nature or because of costs involved in such expansion. As a result of such developments, nowadays people may be living and working closely together. The environments of residential buildings, office buildings, and also other types of buildings, and also such buildings itself, may not always be adapted to cope with this.

[0003] At the same time, since a couple of years there is a tendency for people to work from home at least part of the time. Working from home was even mandatory for many employees during part of the COVID pandemic. Although this may partly neutralize urban areas to become more crowded with employees, it does increase the requirements to the environment of residential buildings. A requirement for people when living and / or working in a building, is an acceptable level of acoustic noise in its environment. This may especially be true for people working from home in a relatively small space, and who wish to go outside of the building during breaks.

[0004] A particular type of acoustic noise is low-frequency acoustic noise. Although other definitions exist, low-frequency acoustic noise may be defined as acoustic noise with a frequency in the range from 20 Hertz to 100 Hertz. While for some people such noise may be tiresome, for other people such noise may even be detrimental to their health (see: G. Leventhall, "Low Frequency Noise. What we know, what we do not know, and what we would like to know", Journal of Low Frequency Noise, Vibration and Active Control, 2009, volume 28, number 2, page 79-104).

[0005] Causes for low-frequency acoustic noise are sometimes unclear, for example because low-frequency acoustic noise can travel over large distances. So, it may be difficult to tackle the problem at the source, as the source may be unknown and difficult to discover. Moreover, it normally is difficult to protect oneself from low-frequency acoustic noise. Earplugs for example can be considered to be not always effective, as low-frequency acoustic noise may still be able to reach the inner ear through bone tissue. Low-frequency acoustic noise forms a problem on its own, separate from acoustic noise at higher frequencies against which one can personally protect oneself better.

[0006] It may thus be clear that there is a need to at least reduce a level of low-frequency acoustic noise in an environment of a building.SUMMARY

[0007] The invention provides a method of covering at least part of a wall of a building by means of a plurality of panels, wherein individual panels of said plurality of panels each include a panel body and have a panel front surface, a panel back surface, and a panel peripheral surface, the method including: positioning the plurality of panels along the wall so that the panel front surfaces face away from the wall, wherein, after the positioning, the panel bodies of the plurality of panels are spaced apart from each other for having a peripheral gap between the panel bodies, and wherein, after the positioning, the panel back surfaces of the plurality of panels are at least partly spaced apart from the wall for having a wall gap between the panel bodies and the wall.

[0008] According to an aspect, the method includes: realising in the wall gap and / or the peripheral gap, by means of the positioning of the plurality of panels, absorption of low-frequency acoustic noise that is generated outside of the building and that propagated towards the wall to reach the wall gap and / or the peripheral gap. According to a further aspect, the method includes: realising, by means of the positioning of the plurality of panels, a reduction of reflection in a direction away from the wall of the building and / or a reduction of transmission into the wall of the building, of low-frequency acoustic noise that is generated outside of the building and that propagated towards the wall to reach the wall gap and / or the peripheral gap.

[0009] Preferably, the low-frequency acoustic noise has a frequency that is at most 100 Hertz. Preferably, the low-frequency acoustic noise has a frequency that is at least 20 Hertz. In an embodiment, frequencies of the low-frequency acoustic noise are in a range from 20 Hertz to 100 Hertz. It was surprisingly found in experiments and numerical simulations that absorption of low-frequency acoustic noise can be realised by dimensioning the panels, the wall gap, and the peripheral gap for that purpose. Without intending to be bound by theory, it is believed that low-frequency acoustic waves may partly cancel out and / or dissipate in the wall gap and / or the peripheral gap. As a result of the absorption, a level of low-frequency acoustic noise in an environment of the building can be reduced.

[0010] In embodiments wherein one or more other buildings are present in an environment of the building, the reduction of low-frequency acoustic noise in an environment of the building can be expected to have a positive effect on noise levels inside the one or more other buildings. After all, if a level of low-frequency acoustic noise in an environment of the building can be reduced, it may be expected that a level of low-frequency acoustic noise is reduced inside the one or more other buildings as well. As a result of the reduced level of low-frequency acoustic noise in said environment, less low-frequency acoustic energy may be available for transmission into the one or more buildings. While low-frequency acoustic noise may be detrimental to one's wellbeing outside of a building, it may also be damaging inside buildings where people stay for many hours each day, such as office buildings and residential buildings.

[0011] Preferably, the panel peripheral surface connects, and / or extends in between, the panel front surface and the panel back surface. Preferably, the panel body has a planar shape. Preferably, a thickness of the panel body varies at most 30 percent of a maximum value of the panel body thickness, more preferably varies at most 15 percent or at most 10 percent of a maximum value of the panel body thickness. The plurality of panels does not necessarily include all panels that cover the at least part of the wall of the building. Optionally, some panels covering the at least part of the wall are not included in said plurality of panels. Preferably, the plurality of panels form one or more groups of neighbouring panels that are separated from at least one other panel of the same group only by the peripheral gap. Preferably, the panel peripheral surfaces of the plurality of panels are spaced apart from each other for having the peripheral gap between the panel peripheral surfaces. Preferably, the panel back surface of the individual panels faces the wall.

[0012] In an embodiment, the individual panels of the plurality of panels are similar, or substantially equal, to each other. Preferably, each of the individual panels has a panel body, a panel front surface, a panel back surface, and a panel peripheral surface that is similar, or substantially equal, to respectively the panel body, the panel front surface, the panel back surface, and the panel peripheral surface of the other individual panels. In another embodiment, one or more of the individual panels has a shape and / or size that differs from one or more other ones of the individual panels. Optionally, a width of the peripheral gap at the panel front surface between a pair of panels of the plurality of panels, may differ at least 20 percent from a width of the peripheral gap between another pair of panels of the plurality of panels. Such variations may influence, in particular may lead to a broadening of, the absorption spectrum of the low-frequency acoustic noise.

[0013] Preferably, the panels each have a panel body that is made of a porous material, or includes at least 50 weight percent or at least 80 weight percent of a porous material. Preferably, said porous material is a fibre cement material. Preferably, a density of the porous material is at least 1200 kilogram per cubic metre and / or is at most 2200 kilogram per square metre. More preferably, the density of the porous material is at least 1600 kilogram. Preferably, the porous material has a porosity of at least 10 volume percent and / or at most 40 volume percent. More preferably, the porous material has a porosity of at least 14 percent and / or at most 24 percent. Preferably, a porosity of the porous material, or at least a porosity of a majority of the porous material, is connected so that the material is permeable.

[0014] The positioning of the plurality of panels along the wall preferably includes attaching the plurality of panels to a frame. The positioning of the plurality of panels along the wall preferably includes attaching the frame to the wall, before or after the panels are attached to the frame. Optionally, the frame is positioned at least partly in the wall gap. In an embodiment, the panels are attached directly to the wall without using the frame.

[0015] In an embodiment, the panel body of each of the individual panels has a planar panel dimension in a direction along the panel front surface of the individual panel. Preferably, the method includes: arranging the planar panel dimension of the plurality of panels, the peripheral gap, and the wall gap so that the absorption of low-frequency acoustic noise that propagated towards the wall to reach the wall gap and / or the peripheral gap, is realised. Preferably, the method includes: arranging the planar panel dimension of the plurality of panels, the peripheral gap, and the wall gap so that the reduction of reflection of low-frequency acoustic noise in a direction away from the wall of the building is realised and / or the reduction of transmission of low-frequency acoustic noise into the wall of the building is realised. Preferably, the planar panel dimension is directed along the front surface of an individual panel.

[0016] In an embodiment, the method includes: arranging the planar panel dimension of the plurality of panels, the peripheral gap, and the wall gap so that low-frequency acoustic noise that propagated towards the wall to reach the wall gap and / or the peripheral gap, at least partly cancels out and / or dissipates in the wall gap and / or the peripheral gap, so that the absorption of low-frequency acoustic noise is realised, the reduction of reflection of low-frequency acoustic noise in a direction away from the wall of the building is realised, and / or the reduction of transmission of low-frequency acoustic noise into the wall of the building is realised. By choosing dimensions of the peripheral gap, the wall gap, and the planar panel dimension of the individual panels of the plurality of panels, absorption, in particular by cancellation and / or dissipation, of part of the low-frequency acoustic noise may be achieved.

[0017] In an embodiment, the panel bodies of the plurality of panels each include a central panel body part, wherein the planar panel dimension extends from the central panel body part to the panel peripheral surface. For example, the planar panel dimension equals half of a width, half of a length, or half of a diameter of a panel body. Preferably, the method includes: arranging the planar panel dimension of the plurality of panels, the peripheral gap, and the wall gap so that a maximum of the absorption of low-frequency acoustic noise is realised at a main absorption frequency of the low-frequency acoustic noise. Preferably, the planar panel dimension is at least 20 Hertz metre divided by said main absorption frequency and / or is at most 160 Hertz metre divided by said main absorption frequency. Optionally, the planar panel dimension ranges from the central panel body part to the panel peripheral surface. Preferably, for at least one of the individual panels, for a majority of the individual panels, or for each of the individual panels, a minimum distance between open parts of the peripheral gap that are at opposite sides of the panel body, and that optionally can be connected by a straight line that goes through the central part of the panel body, is at most 1,3 metre.

[0018] Preferably, said main absorption frequency is at least 20 Hertz and / or at most 100 Hertz, more preferably is at least 40 Hertz and / or at most 90 Hertz. In particular, the main absorption frequency may be in a range from 50 Hertz to 80 Hertz, for example in a range from 60 Hertz to 70 Hertz. Experiments and numerical simulations that were carried out, indicate that, in an embodiment, a reduction of at least about 30 percent can be reached at a main absorption frequency of about 63 Hertz. Preferably, the main absorption frequency is above an audible frequency threshold above which low-frequency acoustic noise is audible for at least some people, preferably for a majority of the people, being confronted with the low-frequency acoustic noise. At least in such embodiments, a reduction in amplitude of the acoustic noise may be appreciated. In an embodiment, at the main absorption frequency, the absorption of acoustic energy, or an absorption coefficient of the plurality of panels, is at least 20 percent, preferably is at least 30 percent, more preferably is at least 40 percent. In particular, at the main absorption frequency, the absorption of acoustic energy, or an absorption coefficient of the plurality of panels, may be at least 50 percent or may be at least 60 percent.

[0019] In an embodiment, the peripheral gap at least partly surrounds the individual panel bodies of the plurality of panels. Preferably, the peripheral gap completely surrounds at least one of, more preferably a majority of, the panel bodies of the plurality of panels. Preferably, the peripheral gap is open or is at least partly open. Preferably, in an open or partly open peripheral gap, air can move into and out of the peripheral gap.

[0020] In one implementation, the panel comprises four peripheral surfaces and the peripheral gap is open along two out of said four peripheral surfaces, but is closed along the other two peripheral surfaces. In a preferred option, the panel has a rectangular or square shape, and the said open gaps are arranged in parallel. More preferably, the gaps extending in the horizontal direction, thus typically between overlying rows of panels, are open, whereas the gaps extending in the vertical direction, thus typically between adjacent panels within a single row, are closed. While it may be beneficial to have an open gap extending fully around the panel, it is deemed practical for sake of fastening and / or decorative purposes that merely the gaps extending in the horizontal direction are open. This facilitates that a vertically extending frame portion can be present behind said closed gap.

[0021] In a further implementation, the assembly of panels arranged along the wall, which assembly is typically referred to as exterior facade, comprises at least a first row, a second row and a third row of panels, wherein a first open gap is present between the first row and the second row, and wherein a second open gap is present between the second row and the third row. It has been found in investigations leading to the invention, that the low noise absorption is significantly larger, when a first and a second open gaps are present above each other.

[0022] Preferably, at the panel front surface, the peripheral gap width is in a range from 4 millimetre to 16 millimetre. More preferably, at the panel front surface, the peripheral gap width is in a range from 6 millimetre to 14 millimetre. The peripheral gap width may for example be about 1 centimetre, at the panel front surface. In a variation, the peripheral gap width at the panel front surface is at least 4 millimetre or at least 6 millimetres, and / or is at most 14 millimetre or at most 16 millimetres. In a variation, the peripheral gap width at the panel front surface is at most 20 millimetres. In a variation, the peripheral gap width at the panel front surface is at most 6 millimetres or is at most 4 millimetres. Preferably, values of the width of the peripheral gap refer to the width of the peripheral gap along a majority of the peripheral gap, preferably along at least 80 percent of the peripheral gap. Optionally, the width of the peripheral gap refers to an average width along the peripheral gap.

[0023] Preferably, a width of the wall gap is at least 50 millimetres and / or at most 400 millimetres. More preferably, the width of the wall gap is at least 100 millimetres and / or at most 300 millimetres. For example, the width of the wall gap is about 0,2 metre. Preferably, the values of the width of the wall gap refer to the width of the wall gap along a majority of the wall gap, preferably along at least 80 percent of the wall gap. Preferably, values of the width of the wall gap disclosed herein refer to the width of the wall gap at a majority, preferably at least 80 percent, of positions where the wall is covered by the plurality of panels. Optionally, the width of the wall gap refers to an average width of the wall gap at positions where the wall is covered by the plurality of panels.

[0024] Preferably, the planar panel dimension, such as e.g. a width or length of the individual panels or about half of the width or length, is at least 300 millimetre and / or is at most 4000 millimetre. For example, the planar panel dimension is approximately 1 metre or approximately 1,5 metre. Experiments and numerical simulations that were carried out indicate that, at least, a peripheral gap width of at least 6 millimetre and / or at most 14 millimetre, a width of the wall gap of at least 100 millimetre and / or at most 300 millimetre, and a width and / or length of a rectangular panel of at least 500 millimetre and / or at most 3000 millimetre, can be expected to enable a significant absorption of low-frequency acoustic noise.

[0025] In an embodiment, the panel body of each of the individual panels has a perimeter that is defined by the panel peripheral surface of the panel body. Preferably, the peripheral gap is open along the perimeter of at least one, preferably of a majority, more preferably of each, of the individual panels, so that the low-frequency acoustic noise can propagate through the open peripheral gap. Preferably, the peripheral gap is open along a part of the perimeter, or along at least part of the perimeter, so that low-frequency acoustic noise can propagate through the open part of the peripheral gap. Preferably, the peripheral gap is open along at least 20 percent, at least 50 percent, or at least 80 percent, of the perimeter so that the low-frequency acoustic noise can propagate through the open part of the peripheral gap.

[0026] In an embodiment, the peripheral gap may be substantially open for parts of the peripheral gap that extend in a substantially sideward direction, while the peripheral gap may be substantially closed for parts of the peripheral gap that extend in a substantially upward direction. In such an arrangement, it may be more difficult for rain to enter the wall gap. As another example, the peripheral gap may be substantially open for parts of the peripheral gap that extend in a substantially upward direction, while the peripheral gap may be substantially closed for parts of the peripheral gap that extend in a substantially sideward direction.

[0027] In an embodiment, the peripheral gap extends in a longitudinal peripheral gap direction in between at least two panel bodies of said plurality of panels. Preferably, the peripheral gap has a peripheral gap width in a direction that is transverse to said longitudinal peripheral gap direction and that is directed from one of the at least two panel bodies to another one of the at least two panel bodies. For example, the direction of the peripheral gap width may be along the panel front surfaces of the at least two panels and / or along the panel back surfaces of the at least two panels. Preferably, along at least part of the peripheral gap, the peripheral gap width increases along a propagation direction of said low-frequency acoustic noise through the peripheral gap towards the wall. Preferably, at the panel front surface the peripheral gap width is smaller than the peripheral gap width at the panel back surface along at least part of the peripheral gap, for example along at least 20 percent of the peripheral gap, along at least 50 percent of the peripheral gap, or along at least 80 percent of the peripheral gap. Such preferred configurations of the peripheral gap width may increase an absorption of low-frequency acoustic noise by means of the panels, while the peripheral gap width at the panel front surface can be kept limited. Such a configuration of the peripheral gap may further hide the wall from view and could also be beneficial in view of regulations on the peripheral gap width at the panel front surface that regulate the peripheral gap width. In particular for a peripheral gap that has a constant width along a direction perpendicular to the panel front surface, such regulations could diminish an effectiveness of the absorption of low-frequency acoustic noise.

[0028] In an embodiment, along at least part of the peripheral gap, a width of the peripheral gap increases along a direction through the peripheral gap towards the wall. Preferably, along at least 20 percent, at least 50 percent, or at least 80 percent, of the peripheral gap, the width of the peripheral gap increases along the direction through the peripheral gap towards the wall.

[0029] In an embodiment, the panel peripheral surfaces of the individual panels are oblique relative to the panel front surfaces of the individual panels along at least part of the peripheral gap, and optionally along substantially the whole peripheral gap. In an embodiment, the panel peripheral surface of at least one, preferably of a majority, more preferably of each, of the individual panels is, along at least part of the peripheral gap, oblique relative to the panel front surface. Preferably, along the at least part of the peripheral gap, an angle between the panel peripheral surface and the panel front surface of the individual panels is in a range from 20 degrees to 70 degrees. Preferably, along the at least part of the peripheral gap, for example along at least 20 percent of the peripheral gap, preferably along at least 50 percent of the peripheral gap, or more preferably along at least 80 percent of the peripheral gap, an angle between the panel peripheral surface and the panel front surface of the at least one individual panel, of the majority of the individual panels, or of each individual panel, is in a range from 20 degrees to 70 degrees, preferably is in a range from 30 degrees to 60 degrees, for example is about 45 degrees. As a result, in an embodiment, at the panel front surface the peripheral gap width may be smaller than the peripheral gap width at the panel back surface. Preferably, at the panel back surface, the peripheral gap width is at least 1,2 times, preferably at least 1,5 times, more preferably at least 2 times or at least 3 times, the peripheral gap width at the panel front surface along the at least part of the peripheral gap, e.g. along at least 30 percent of the peripheral gap. Said angle, said obliqueness, and / or said difference between the peripheral gap width at the panel front surface and the peripheral gap width at the panel back surface, preferably extend along at least 50 percent of the peripheral gap.

[0030] In an embodiment, the panel peripheral surfaces of the individual panels are, at least partly or substantially completely, oblique relative to the panel front surfaces of the individual panels along open parts of the peripheral gap. Preferably, the panel peripheral surfaces of the individual panels are, at least partly or substantially completely, at a substantially right angle relative to the panel front surfaces of the individual panels along closed parts of the peripheral gap. In an embodiment, the panel bodies of the plurality of panels each have a panel peripheral surface that is, relative to the panel front surface, oblique along part of the panel peripheral surface and at a substantially right angle along another part of the panel peripheral surface. A panel peripheral surface that is at such a substantially right angle may be more easily closed and / or may be less easily damaged during the closing of the peripheral gap. A panel peripheral surface having an oblique angle may increase the absorption of low-frequency acoustic noise while still meeting regulations with respect to an allowable width of the peripheral gap.

[0031] In an embodiment, the panel bodies of the plurality of panels each have at least three, preferably four or at least four, corners and have a panel peripheral surface that is, relative to the panel front surface, oblique along part of the panel peripheral surface. In an embodiment, said panel peripheral surface is at a substantially right angle to the panel front surface at at least one of the corners, preferably at a pair of the corners, more preferably at all of the corners, of each of the panel bodies. Preferably, for each of the individual panels, in between at least one pair of the corners the panel peripheral surface is partly oblique relative to the panel front surface, preferably is oblique relative to the panel front surface along at least 20 percent, at least 50 percent, or at least 80 percent of a distance between said pair of corners. Preferably, the pair of corners, and / or the at least one pair of corners, is formed by corners that are neighbouring to each other. Having such a substantially right angle at one or more corners could lead to a less vulnerable panel.

[0032] In an embodiment, the plurality of panels each have a rectangular shape, said rectangular shape defining a longitudinal panel direction of the panels. According to an option, parts of the panel peripheral surfaces that extend along the longitudinal panel direction are oblique relative to the panel front surfaces, while the panel peripheral surfaces that extend transverse to the longitudinal panel direction are at a substantially right angle relative to the panel front surfaces. According to another option, parts of the panel peripheral surfaces that extend in a direction that is transverse to the longitudinal panel direction are oblique relative to the panel front surfaces, while the panel peripheral surfaces that extend in the longitudinal panel direction are at a substantially right angle to the panel front surfaces. Both options enable parts of the panel peripheral gap that extend in one, preferably substantially horizontal or otherwise sideward, direction to be open and be provided with an oblique panel peripheral surface, while parts of the panel peripheral gap that extend in another, preferably substantially vertical or otherwise upward, direction are closed.

[0033] In an embodiment, the method includes providing, in the wall gap, a damping material that is arranged for damping the low-frequency acoustic noise. Preferably, said damping material is a mineral wool such as rock wool. Preferably, a majority of the wall gap is filled with the damping material. The damping material may further promote the absorption of the low-frequency acoustic noise in the wall gap. Thus, preferably, mineral wool or another material that can dampen low-frequency acoustic noise, is provided in the wall gap.

[0034] In an embodiment, the panel back surface of at least one, preferably of a majority, more preferably of each, of the individual panels is provided with a ridge. Preferably, the at least one ridge or the ridges, after the positioning of the plurality of panels, partitions the wall gap in order to create at least two cavities in the wall gap. Preferably, the at least two cavities are in fluid communication with the peripheral gap so that the low-frequency acoustic noise can propagate through the peripheral gap into the cavities in the wall gap. Optionally, by means of the one or more ridges, the panels are attached to the wall, optionally without using the frame. Preferably, the method includes positioning the one ore more ridges in contact with the wall. The at least one ridge enables to adjust acoustic properties of the wall gap. The at least one ridge may enable a better control of the absorption of acoustic noise. Preferably, the at least two cavities have volumes that differ from each other, so that a resonance frequency of one of the at least two cavities is different from, e.g. is at least 120 percent of, another one of the at least two cavities. Instead of one main absorption frequency in the low-frequency range, more than one main absorption frequency may be obtained as a result of the cavities having different acoustic properties. Thus, optionally, a broader frequency range may be obtained wherein the absorption of low-frequency acoustic noise is significant.

[0035] In an embodiment, the ridge is formed by the frame to which the plurality of panels is attached or is to be attached. In an embodiment, the frame may be designed for partitioning the wall gap for forming the at least two cavities. In another embodiment, the ridge is part of the panel, e.g. is integral to the panel. For example, the ridge and the remainder of the panel can be made of one part. The ridges may be attached to the panels before the panels are attached to the frame and / or to the wall. Optionally, a number of ridges of the plurality of panels are part of a panel and a number of ridges are formed by the frame.

[0036] In an embodiment, the wall faces another wall that is covered by means of a method according to the invention, so that low-frequency acoustic noise that is reflected from the wall can propagate towards said other wall. The wall and the other wall may for example be at opposite sides of a street. The wall and the other wall may for example be part of separate buildings. In an embodiment, along the street, a plurality of buildings (or, in other words, a group of buildings) is provided. The method may include covering at least part of a wall of each building of the plurality of buildings using a method according to the invention, so that low-frequency acoustic noise that is reflected from the wall of one building of the plurality of buildings can propagate towards the wall of another building of the plurality of buildings. Preferably, the wall of said one building and the wall of said another building both face the street. If reflected acoustic noise is also absorbed by means of a plurality of panels on said another building, reducing the amplitude of the low-frequency acoustic noise in an environment of both buildings may be realised effectively.

[0037] In an embodiment, the planar panel dimension, the peripheral gap and / or the wall gap of the plurality of panels positioned along the wall is different from, e.g. is at least 120 percent of, respectively the planar panel dimension, the peripheral gap and / or the wall gap of the plurality of panels along the other wall. Preferably, a frequency of low-frequency acoustic noise at which a maximum in the absorption is reached by means of the plurality of panels covering the wall, is different from, e.g. is at least 120 percent of, another frequency of low-frequency acoustic noise at which a maximum in the absorption is reached by means of the plurality of panels covering the other wall. Preferably, a frequency of the low-frequency acoustic noise at which a maximum of the reduction of the reflection from and / or transmission through the wall is reached, is different from, e.g. is at least 120 percent of, a frequency of the low-frequency acoustic noise at which a maximum of the reduction of the reflection from and / or of the transmission through the other wall is reached. In such an embodiment, preferably, a difference between said frequency and said other frequency is at least 30 Hertz, more preferably at least 50 Hertz. In these embodiments, the low-frequency acoustic noise may be absorbed more evenly along a wider frequency range, compared with the situation that both the wall and said other wall are covered in the same way.

[0038] Preferably, the plurality of panels forms a facade covering the at least part of the wall of the building. Preferably, the facade has an aperture ratio that is defined as the ratio of an area, measured along the panel front surfaces, of an open part of the facade, preferably formed by the open part of the peripheral gap, and a closed part of the facade, preferably formed by the plurality of panels. In an embodiment, the facade has an aperture ratio of at most 0,02, preferably at most 0,01, more preferably at most 0,005. Significant absorption effects were found in experiments wherein an aperture ratio was in a range from 0,002 to 0,007. Preferably, the facade has an aperture ratio of at least 0,001, optionally of at least 0,002, at least 0,003, or at least 0,004.

[0039] The invention also provides use of a plurality of panels for covering at least part of a wall of a building, wherein individual panels of said plurality of panels each include a panel body and have a panel front surface, a panel back surface, and a panel peripheral surface, the use including: positioning the plurality of panels along the wall so that the panel front surfaces face away from the wall, wherein, after the positioning, the panel bodies of the plurality of panels are spaced apart from each other for having a peripheral gap between the panel bodies, and wherein, after the positioning, the panel back surfaces of the plurality of panels are at least partly spaced apart from the wall for having a wall gap between the panel bodies and the wall. Preferably, such use is combined with one or more embodiments, features, variations, or examples of a method disclosed herein.

[0040] According to an aspect, the use includes: realising in the wall gap and / or the peripheral gap, by means of the positioning of the plurality of panels, absorption of low-frequency acoustic noise that is generated outside of the building and that propagated towards the wall to reach the wall gap and / or the peripheral gap. According to a further aspect, the use includes: realising, by means of the positioning of the plurality of panels, a reduction of reflection in a direction away from the wall of the building and / or a reduction of transmission into the wall of the building, of low-frequency acoustic noise that is generated outside of the building and that propagated towards the wall to reach the wall gap and / or the peripheral gap.

[0041] The invention also provides a panel that is arranged for covering at least part of a wall of a building, wherein the panel includes a panel body and has a panel front surface, a panel back surface, and a panel peripheral surface. Preferably, the panel is arranged for being positioned along the wall so that the panel front surface faces away from the wall and at least part of the panel back surface is spaced apart from the wall. Preferably, at least part of the panel peripheral surface is oblique relative to the panel front surface. Preferably, an angle between the panel peripheral surface and the panel front surface is in a range from 20 degrees to 70 degrees. Thus, preferably, the panel peripheral surface is, along at least part of the panel peripheral surface, oblique relative to the panel front surface. Preferably, along the at least part of the panel peripheral surface, an angle between the panel peripheral surface and the panel front surface is in a range from 20 degrees to 70 degrees.

[0042] According to an aspect, the wall gap and / or the peripheral gap is arranged for absorbing low-frequency acoustic noise that is generated outside of the building and that propagated towards the wall to reach the wall gap. According to a further aspect, the wall gap and / or the peripheral gap is arranged for reducing reflection in a direction away from the wall of the building and / or reducing transmission into the wall of the building, of low-frequency acoustic noise that is generated outside of the building and that propagated towards the wall to reach the wall gap and / or the peripheral gap.

[0043] In an embodiment, the panel is one of a plurality of panels, wherein the individual panels of the plurality of panels preferably are similar. Preferably, the features of the panel are also implemented in each other panel of the plurality of panels. This plurality of panels can be used in a method, a use, or an assembly according to the invention.

[0044] In an embodiment, the panel body of each of the individual panels has a perimeter that is defined by the panel peripheral surface of the panel body. Preferably, the panel peripheral surface is oblique relative to the panel front surface along at least 20 percent of the perimeter, preferably at least 50 percent of the perimeter, more preferably at least 80 percent of the perimeter. In an embodiment, the panel peripheral surface is oblique relative to the panel front surface along at least 20 percent of the panel peripheral surface, preferably at least 50 percent of the panel peripheral surface, more preferably along at least 80 percent of the panel peripheral surface. Optionally, other parts of the panel peripheral surface are at a substantially right angle to the panel front surface.

[0045] In an embodiment, the panel has a rectangular shape, said rectangular shape defining a longitudinal panel direction of the panel. According to an option, a part of the panel peripheral surface that extends along the longitudinal panel direction is oblique relative to the panel front surface, while a part of the panel peripheral surface that extends transverse to the longitudinal panel direction is at a substantially right angle relative to the panel front surface. According to another option, a part of the panel peripheral surface that extends in a direction that is transverse to the longitudinal panel direction is oblique relative to the panel front surfaces, while a part of the panel peripheral surface that extends along the longitudinal panel direction is at a substantially right angle relative to the panel front surface.

[0046] The invention also provides an assembly of a plurality of panels and a wall of a building, wherein the plurality of panels covers at least part of the wall of the building, wherein individual panels of said plurality of panels each include a panel body and have a panel front surface, a panel back surface, and a panel peripheral surface, wherein the plurality of panels is positioned along the wall so that the panel front surfaces face away from the wall, wherein the panel bodies of the plurality of panels are spaced apart from each other so that the plurality of panels has a peripheral gap between the panel bodies, and wherein the panel back surfaces of the plurality of panels are at least partly spaced apart from the wall so that the assembly defines a wall gap between the panel bodies and the wall. According to an aspect, the plurality of panels is arranged and positioned for realising, in the wall gap and / or the peripheral gap, absorption of low-frequency acoustic noise that is generated outside of the building and that propagated towards the wall to reach the wall gap and / or the peripheral gap. According to a further aspect, the plurality of panels is arranged and positioned for reducing reflection in a direction away from the wall of the building and / or reducing transmission into the wall of the building, of low-frequency acoustic noise that is generated outside of the building and that propagated towards the wall to reach the wall gap and / or the peripheral gap.

[0047] Preferably, the assembly is used in a method according to the invention and / or in a use according to the invention. Preferably, the assembly includes one or more panels according to the invention. Optionally, each of the individual panels is a panel according to the invention.

[0048] As described above, the present disclosure relates to a method, a use, a panel, and an assembly. Any feature, example, variation, or embodiment disclosed herein in relation to at least one of said method, use, panel, and assembly, may also be applied in relation to the other ones of the method, use, panel, and assembly.BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The invention will be illustrated with reference to the following non-limiting figures, wherein: Figures 1A-1D shows different examples of a plurality of panels that cover at least part of a wall of a building; Figure 2A schematically shows the plurality of panels in a cross section indicated in figure 1A; Figure 2B schematically shows the plurality of individual panels in a cross similar crosse section similar to the one in figure 2A, however in another embodiment; Figures 3A-3I schematically show, in a back side view, different examples of an individual panel having an oblique panel peripheral surface or an oblique part of the panel peripheral surface; Figure 4 shows a detail indicated in figure 2A; Figure 5A shows absorption coefficients α S that are determined based on measurements in a reverberation room, in five different experiments; Figure 5B shows absorption coefficients α S that are determined in three different numerical simulations; Figure 6A schematically shows a transparent top view of a panelling design that was used in the experiments; Figure 6B schematically shows a transparent top view of another panelling design that was used in the experiments; Figure 6C shows a cross section indicated in figure 6A; Figure 7A shows a plurality of panels in a back side view, when being positioned along a vertical wall; Figure 7B shows the plurality of panels of figure 7A in a top view of a horizontal cross section through the vertical wall, when being positioned along the vertical wall; and Figure 8 schematically shows, in a top view, a plurality of buildings, each at least partly covered by means of a plurality of panels. DETAILED DESCRIPTION

[0050] The present disclosure relates to a method of covering at least part of a wall of a building by means of a plurality of panels, directed to the purpose of absorbing low-frequency acoustic noise. Such noise may e.g. be generated in, or may propagate into, an environment of the building and propagate towards the wall. The panels may be of various shape and composition. For example, the panels may each have a panel body that is made of fibre cement material, or at least includes 50 weight percent fibre cement material. Fibre cement material is a material that includes cement and fibers, and that thus may be regarded as a composite material. The fibers may be cellulose fibers and / or synthetic fibers. The manufacture of fibre cement material is known as such. Panels with another composition may be used alternatively or additionally to panels that include a fibre cement material. Preferably, the body of the panels includes a porous material. The porous material may e.g. have a porosity in a range from 10 percent to 40 percent, preferably in a range from 14 percent to 24 percent. The porosity may, at least partly, be connected. Optionally, the porous material is permeable.

[0051] The use of a plurality of panels for covering a wall of a building for decorative purposes is known as such. Architects or other designers have designed individual buildings that are provided with such panels. For such decorative purposes, panels having a body that is made of a fibre cement material are also used. Against the background of such use of panels for decorative purposes, it was surprisingly found that the plurality of panels can also be used for absorbing low-frequency acoustic noise. Although some types of decorative panels may be not, or may be less, suitable for the purpose of absorbing low-frequency acoustic noise, other decorative panels may be used in a method, a use and / or an assembly according to the present disclosure. Additionally or alternatively to known decorative panels, other panels may be used. A panel thickness of the panels, and / or a thickness of bodies of the panels, may be in a range from 6 millimetres to 15 millimetres, in particular may be about 8 millimetres or about 12 millimetres. The panels and / or the panel bodies may for example have a width in a range from 0,3 metre to 2 metres, for example about 1 metre or about 1,2 metre, and / or may have a length in a range from about 1 metre to about 4 metres, for example about 1 metre, about 2 metres, or about 3 metres. However, optionally, panels and / or panel bodies that have another width, have another length, and / or have another thickness, may also be suitable.

[0052] The plurality of panels used in a method, use or assembly according to the present disclosure, may be part of a cladding system that further includes a frame. Along the wall of the building, the cladding system may form a facade that extends along the wall and that includes the panels as an outer surface. The panels of the cladding system may be fastened onto the frame of the cladding system. The frame may be fixed or otherwise attached to the wall, or to another support structure which is attached to the wall. A wall gap that e.g. can be used for ventilation may be present behind the panels. In addition, there may be a space (or, in other words, a peripheral gap) provided in between the panels. The wall gap and open parts of said space may be useful for regulating humidity and temperature of the panels and allow for some temperature-induced expansion (or, in other words, dilatation) of the panels. A gap, closed or open, between panels may even be mandatory to allow for the dilatation of the panels. Often the peripheral gap is closed with a closing element. The closing element may be applied from the back surface or from the front surface of the panel, to obtain protection against intrusion of water and wind. Such closing elements are known as such to the skilled person.

[0053] The present disclosure is directed i.a. to the use of a plurality of panels as a facade with open or partly open joints (or, in other words, an open or partly open gap) in between adjacent panels, for the purpose of realising absorption of low-frequency acoustic noise. Moreover, for this purpose, additional features to the positioning and arrangement of the panels can be introduced, as will be described herein. Experiments and numerical simulations that were carried out, surprisingly show that a significant reduction of low-frequency acoustic noise may be achieved by choosing panel dimensions and open gap dimensions directed to this purpose. Surprisingly, significant effects were found in experiments wherein an aperture ratio of an engineering model that resembled a facade that includes the plurality of panels, was within a range from approximately 0,002 to approximately 0,007. It thus was found that acoustic noise can be reduced significantly in the low-frequency range, in particular around 60 to 70 Hertz. For example, a significant effect was found in a range from 50 Hertz to 100 Hertz, in particular in a range from 50 Hertz to 70 Hertz. Typically, in such ranges, low-frequency acoustic noise generated by aircrafts can be relatively strong and low-frequency acoustic noise generated by road traffic, such as cars and trucks, can also be considerable.

[0054] Low-frequency acoustic noise may be defined as having a frequency that is at most 100 Hertz and optionally at least 20 Hertz. Low-frequency acoustic noise can originate from different sources, including traffic of for example cars, trucks, trains, or airplanes. Another source can be wind energy turbines. Low-frequency acoustic noise may be generated together with acoustic noise having higher frequencies. In view of low-frequency acoustic noise that nowadays is recognized as being problematic or detrimental, possibilities for realising absorption, or for reducing the reflection from a building and / or the transmission into a building, of low-frequency acoustic noise may be appreciated.

[0055] The experimental and numerical results indicate that, by means of the plurality of panels covering at least part of the wall of a building, in practical situations significant absorption of low-frequency acoustic noise can be realised. Such low-frequency acoustic noise may be generated outside of the building and may have propagated towards the wall. The low-frequency acoustic noise is absorbed in the peripheral gap formed by the space between the panels and / or in the wall gap formed by a space between the wall and panel back sides of the plurality of panels. The results of the experiments and of the numerical simulations indicate that such absorption can be optimized by choosing, among other parameters, a planar panel dimension of the panels and dimensions of the peripheral gap between the panels. Said planar panel dimension may be defined as a, preferably shortest, distance from a central part of the panel body to a position on the panel peripheral surface where the peripheral gap is open. For example, for a rectangular panel the planar panel dimension may half a width the panel or half a length of the panel.

[0056] Often, an open peripheral gap between panels is prevented. This may be for aesthetic reasons (for example because a closed peripheral gap contributes to hiding the frame from view), but also in order to prevent rain and wind to enter the wall gap. The peripheral gap may be closed e.g. by means of tape or by means of a T-shaped closing element that can be pushed between the panels. Other manners of closing the peripheral gap can also be used. When large areas are covered, leaving some parts of the peripheral gap open could be beneficial for ventilation of the wall gap, also in view of regulating temperature and humidity. Leaving open significant parts of the peripheral gap however, for example more than 50 percent or more than 80 percent of the peripheral gap, goes against a common preference for closing at least most of the peripheral gap between the panels. Such preference may for example be based on the aim to prevent wind, rain, sand, or rubbish that can be lifted by the wind, to enter the wall gap.

[0057] According to the present disclosure, the peripheral gap may be in fluid communication with (or, in other words, may be fluidly connected to) the wall gap between a body of the panels and the wall. As a result, air can move from the peripheral gap into the wall gap and from the wall gap into the peripheral gap, as a result of propagation of low-frequency acoustic noise. Thus, the low-frequency acoustic noise can propagate through air, from the peripheral gap into the wall gap and vice versa. The wall gap and the peripheral gap may preferably be dimensioned, relative to dimensions of the panels itself, so that low-frequency acoustic noise that propagated through the peripheral gap into the wall gap at least partly cancels out low-frequency acoustic noise that propagated through the central part of the panel body into the wall gap. Such cancelling out may, partly or completely, be the result of destructive interference of low-frequency acoustic noise in the wall gap and / or the peripheral gap. Alternatively, or additionally, the wall gap and the peripheral gap may be dimensioned, relative to dimensions of the panels itself, so that low-frequency acoustic noise that propagated, through the peripheral gap and / or through the central part of the panel body, into the wall gap, is at least partly dissipated. Such dissipation may in particular take place in the peripheral gap. Although such mechanisms can be considered for explaining the experimental results, they are not intended as being limiting to the present disclosure.

[0058] The present disclosure moreover recognises that, in order to combine an effective absorption of low-frequency acoustic noise with one or more other desired properties of the peripheral gap (such as aesthetic properties), it may be advantageous to have a panel peripheral surface that is, partly or completely, oblique relative to the panel front surface. In an embodiment, at least part of the panel peripheral surface of at least one, preferably of each, of the individual panels of the plurality of panels is oblique relative to the panel front surface. Preferably, an angle between the panel peripheral surface and the panel front surface is in a range from 20 degrees to 70 degrees.

[0059] It may thus be clear that panels that are intended for covering at least part of a wall of a building for decorative purposes, but also other panels, can be used for the purpose of absorbing low-frequency acoustic noise that is generated outside of the building and that propagated towards the wall. Such use of panels may be beneficial to the health of people that are in an environment of the building, and possibly live or work in or around said building. The panels may be adapted or optimized for reducing an amount of low-frequency acoustic noise, e.g. by optimizing their composition, porosity, shape, size, and positioning relative to each other. As a result of the absorption, it moreover can be expected that the panels can be used for reducing the reflection in a direction away from the wall of the building and / or for reducing a transmission into the wall of the building, of low-frequency acoustic noise that is generated outside of the building and that propagated towards the wall. Without wanting to be bound by theory, said reducing of the reflection and / or the transmission may originate from a loss of acoustic energy as a result of the absorption. The absorption may cause less acoustic energy to be available for the reflection and / or the transmission.

[0060] In this way, a less noisy environment may be realised (or in other words, achieved) in an environment of the building. The environment may e.g. be within a substantially horizontal distance of 100 metres from the building, or within a substantially horizontal distance of 300 or 500 metres from the building. In addition, less low-frequency acoustic noise may possibly be present also inside the building. For example, the less noisy environment may diminish an amount of low-frequency acoustic noise to reflect back to the building. Such reductions in low-frequency acoustic noise may be appreciated in particular when the building is next to a motorway (e.g. is within 100, 300, or 500 metres of a motorway) while the wall faces the motorway. A less noisy environment may also be appreciated if the wall faces a garden of a house that experiences low-frequency acoustic noise, e.g. generated by traffic on a motorway of by airplanes. Realising a less noisy environment by means of the plurality of panels may be even more effective if applied to several buildings that face each other and preferably are in an environment of each other. For a peripheral gap having, along at least part of the peripheral gap, a width that increases along a direction through the peripheral gap towards the wall, the plurality of panels may be relatively effective in absorption of low-frequency acoustic noise while at the panel front surface the peripheral gap width can be limited.

[0061] Figures 1A-1D show different examples of a plurality of panels 2 that cover at least part of a wall of a building. The wall is not indicated in figures 1A-1D, but examples of the wall are indicated in figures 2A, 2B, 4, 7B, and 8 with reference number 4, 4.1, or 4.2. Individual panels 2 of the plurality of panels may have the form of a polygon with three or four corners, examples of which are shown in figures 1A-1D. The individual panels 2 may e.g. have a rectangular shape, as shown in figures 1A-1C. Alternatively, or additionally, the individual panels 2 of the plurality of panels may have a similar size and shape, an example of which is illustrated in figure 1A. Alternatively, a number of the individual panels 2 may have a shape and / or size that differs from other ones of the individual panels 2, as shown in figures 1B-1D. Individual panels 2 that are similar and / or have a rectangular shape may provide the advantage of being more easy to position along the wall. It however may be clear from figures 1A-1D that the plurality of panels 2 used for covering the at least part of the wall may be selected from many different shapes and sizes. A width M (indicated in figures 2A and 2B) of the panels may for example be about 1220 millimetre. A panel length, measured in a direction that is perpendicular to the direction in which the width M is measured, may for example be about 2500 millimetre or about 3050 millimetres.

[0062] Figure 2A schematically shows the plurality of individual panels 2 in a cross section A-A' indicated in figure 1A. Figure 2B schematically shows a plurality of individual panels 2 in a cross section similar to the one in figure 2A, however in another embodiment. Figure 4 shows a detail B indicated in figure 2A. The individual panels 2 cover at least part of the wall 4. The individual panels 2 each include a panel body 6. Each of the individual panels also has a panel front surface 8, a panel back surface 10, and a panel peripheral surface 12. The panel front surface 8, the panel back surface 10 and / or the panel peripheral surface 12, or a part thereof, may be formed by a surface layer or other finishing that is provided on the panel body 6 and that is different from the panel body. The finishing may e.g. be paint. Alternatively, or additionally, the panel front surface 8, the panel back surface 10 and / or the panel peripheral surface 12, or a part thereof, may be formed by an outer surface of the panel body itself. For example, the panel body may initially be positioned without any finishing and could be painted only after being positioned along the wall.

[0063] Two methods according to two different embodiments of the invention are illustrated with reference to figure 2A respectively figure 2B. The methods include covering at least part of the wall 4 of a building by means of the plurality of panels 2. The methods further include positioning the plurality of panels 2 so that the panel front surfaces 8 face away from the wall. After the positioning, the panel bodies 6 of said plurality of panels are spaced apart from each other for having a peripheral gap 14 between the panel bodies 6, as illustrated for example in figures 1A-1D, 2A, 2B, and 4. More in general, the peripheral gap may be shaped as a lattice that extends in between the panels. The lattice may for example have regular and rectangular lattice elements (such as in figure 1A), may have irregular and rectangular lattice elements (such as in figures 1B and 1C), and / or may have other irregular lattice elements (such as in figure 1D). After the positioning, the panel back surfaces 10 of the panels 2 are at least partly spaced apart from the wall 4 for having a wall gap 16 between the panel bodies 6 and the wall 4. As illustrated in figures 1A-1D, the plurality of panels 2 may form a group of panels. Each panel of the group of panels may be neighbouring to at least one other panel of the group of panels. Each panel of the group of panels may be separated from at least one other panel of the group of panels only by the peripheral gap 14.

[0064] The positioning of the plurality of panels along the wall may include attaching the plurality of panels to a frame. This may be done by conventional ways of attaching, such as attaching by means of screws. The positioning of the plurality of panels along the wall may further include attaching the frame to the wall. This may also be done by means of conventional ways of attaching, such as attaching by means of bolts. The frame may e.g. include aluminium and / or wood. Normally, the frame is positioned at least partly in the wall gap 16. In some variations, the frame may also fill part of the peripheral gap 14. In some embodiments, a width W of the wall gap 16 (indicated in figures 2A and 2B and also identifiable in figures 4, 6C, 7B and 8) may for example be at least 100 millimetres and / or may be at most 300 millimetres, for example may be about 200 millimetres.

[0065] Figures 1A-1D indicate that the peripheral gap 14 may surround, partly or completely, the panel bodies 6 of the plurality of panels 2. Thus, the peripheral gap may extend along at least part of a perimeter (indicated with reference number 20 in figure 1A) of the panel bodies 6. The peripheral gap is open or is partly open. In an open peripheral gap, and in open parts of the peripheral gap, the peripheral gap is filled with air while air can freely move through the peripheral gap towards the wall gap and vice versa. Preferably, the peripheral gap is open along the perimeter of the bodies 6 of the individual panels 2. The perimeter 20 may be defined by the panel peripheral surface 12 of the panel body. As indicated in figures 1A and 1D, the peripheral gap 14 extends in a longitudinal peripheral gap direction 13 in between at least two panel bodies 6 of said plurality of panels 2. The peripheral gap, as indicated in figures 2A and 2B, has a width N in a direction that is transverse, e.g. perpendicular, to said longitudinal peripheral gap direction 13 and that is along, e.g. perpendicular with, the panel front surfaces 8 of the at least two panels 2. In the embodiment illustrated with reference to figure 2A, the width N shown is substantially constant along the propagation direction 18 of the low-frequency acoustic noise through the peripheral gap 14 towards the wall 4. In the embodiment illustrated with reference to figure 2B however, the width shown increases along said propagation direction 18.

[0066] As illustrated in the embodiment of figure 2B, the panel peripheral surfaces 12 of the individual panels 2 may be oblique relative to the panel front surfaces 8 of the individual panels. Along at least part of the peripheral gap 14, the width N of the peripheral gap 14 may increase along a direction 19 through the peripheral gap towards the wall 4. The width N of the peripheral gap may increase along the direction 19 through the peripheral gap towards the wall, along at least 20 percent, at least 50 percent, or at least 80 percent of the peripheral gap 14. An angle β between the panel peripheral surface and the panel front surface 8 may be in a range from 20 degrees to 70 degrees, preferably in a range from 30 degrees to 60 degrees, for example approximately 45 degrees. If the angle is too large (i.e. too close to 90 degrees), an effect of the angle will be relatively small. If the angle is too small, the panel may become relatively thin and vulnerable. The obliqueness as described herein may enable the peripheral gap to appear closed, or almost closed, to an observer looking to the front surfaces of the plurality of panels, for example because at the panel front surface the peripheral gap width is at most 4 millimetre or at most 6 millimetres. As indicated in figure 2B, at the panel front surface 8 the peripheral gap width N may have its smallest value. At the same time, the obliqueness may enable the peripheral gap 14 to be still effective for absorbing low-frequency acoustic noise.

[0067] Oblique panel peripheral surfaces may be applied along at least part of the peripheral gap, and optionally along substantially the whole peripheral gap. Oblique panel peripheral surfaces may be applied at open parts of the peripheral gap. As will later be illustrated with reference to figure 5B, such an angle may increase the absorption of low-frequency acoustic waves. Hence, by means of a panel peripheral surface with such an angle, the plurality of panels 2 may better absorb low-frequency acoustic noise that is generated outside of the building and that propagated towards the wall. As shown in figure 5B, such an effect may in particular be achieved when the peripheral gap width N at the front surface is in a range from 6 millimetres to 14 millimetres, and in particular is about 8 millimetres. An oblique peripheral gap may also be beneficial in view of regulations on the peripheral gap width at the panel front surface, which may limit in practice the peripheral gap width that can be applied. Along parts of the peripheral gap where the peripheral gap is closed, the peripheral gap may be at a substantially right angle to the panel front surface. Such a right angle may facilitate the closing of the peripheral gap.

[0068] For example, in the example of figures 1B and 1C, the plurality of panels each have a rectangular shape that defines a longitudinal panel direction of the panels. The longitudinal panel direction is in a horizontal direction in figure 1B, and is in a vertical direction in figure 1C. In the example of figure 1B, the parts of the panel peripheral surfaces that extend in the longitudinal panel direction may be partly or completely oblique, while the parts of the panel peripheral surfaces that extend transverse to the longitudinal panel direction may be at a substantially right angle to the panel front surface. In the example of figure 1C, the parts of the panel peripheral surfaces that extend in a direction that is transverse to the longitudinal panel direction may be partly or completely oblique, while the panel peripheral surfaces that extend in the longitudinal panel direction may be at a substantially right angle to the panel front surface. As a result, in both figures 1B and 1C, horizontal parts of the panel peripheral gap may be open or partly open and may be provided with an at least partly oblique panel peripheral surface, while vertical parts of the panel peripheral gap may be closed.

[0069] Figures 3A-3I each schematically illustrate different examples of an individual panel 2. Each of the panels 2 of figures 3A-3I may be one of a plurality of panels that can be used in a method, use, or assembly according to the present disclosure. The individual panels of said plurality may be similar to each other. Thus, the features of a panel 2 shown in one of figures 3A-3I, may also be implemented in a majority of, or in each of, the other panels of the plurality of panels. The plurality of panels can be used in a method, a use, or an assembly according to the present disclosure. A transition 15 from the panel back surface 10 to the panel peripheral surface 12 is schematically indicated in figures 3A-3I as well. In figure 3C, the whole of the panel peripheral surface 12 is oblique relative to the panel front surface (not visible in figures 3A-3I). In the other ones of figures 3A-3I, part of the panel peripheral surface 12 is oblique relative to the panel front surface. Other parts of the panel peripheral surface 12 may be at a substantially right angle to the panel front surface.

[0070] In the present disclosure, a substantially right angle may refer to an angle within the range from 70 degrees to 110 degrees, preferably to an angle within the range from 80 degrees to 100 degrees. Hence, a substantially right angle may deviate plus or minus 10 degrees, or plus or minus 20 degrees, from a right angle of 90 degrees. In case the panel front surface includes irregularities, such as for example channels in the panel front surface, the panel front surface can be considered to coincide with the top parts of the panel front surface. The panel front surface may e.g. be defined such that it is planar and that all of the panel body is behind the panel front surface. Along the oblique panel peripheral surface 12, and / or along the oblique part of the panel peripheral surface 12, an angle β (illustrated in figure 2B) between the panel peripheral surface 12 and the panel front surface may be in a range from 20 degrees to 70 degrees.

[0071] As indicated in figures 3A-3I, the panel 2 may have a substantially rectangular shape. The rectangular shape may define a longitudinal panel direction 17 of the panel 2. A part of the panel peripheral surface 12 that extends along the longitudinal panel direction 17 may be oblique relative to the panel front surface. This can be seen e.g. in figures 3A, 3C, 3D, 3F, 3H, and 3I. In all of figures 3A-3I except figures 3B and 3C, a part of the panel peripheral surface that extends transverse to the longitudinal panel direction 17 is at a substantially right angle relative to the panel front surface. A part of the panel peripheral surface 12 that extends in a direction that is transverse to the longitudinal panel direction 17, may at least partly be oblique relative to the panel front surface. Examples of this feature can be seen in figures 3B, 3C, 3E, 3F, and 3G. In all of figures 3A-3I except figures 3A and 3C, a part of the panel peripheral surface that extends along the longitudinal panel direction is at a substantially right angle relative to the panel front surface.

[0072] In an embodiment, at least 20 percent of the panel peripheral surface is oblique relative to the panel front surface or at least 50 percent of the panel peripheral surface is oblique relative to the panel front surface. The latter feature is implemented in figures 3A, 3C, and 3D. In for example figure 3C, at least 80 percent of the panel peripheral surface is oblique relative to the panel front surface. Parts of the panel peripheral surface 12 that are not visible in the back side view of figures 3A-3I, may be at a substantially right angle to the panel front surface. In an embodiment, at least a part of the panel peripheral surface 12 that extends along the longitudinal panel direction 17 and at least a part of the panel peripheral surface 12 that extends transverse to the longitudinal panel direction 17, are oblique relative to the panel front surface. Examples of this feature are visible in figures 3C and 3F. In an embodiment, parts of the panel peripheral surface 12 that are located opposite to each other and / or are at opposite sides of the panel body, are oblique relative to the panel front surface. Examples of this feature are visible in figures 3A, 3B, 3C, 3D, 3E, 3H, and 3I. In an embodiment, a part of the panel peripheral surface 12 that extends along the longitudinal panel direction 17 and a part of the panel peripheral surface 12 that extends in a direction transverse to the longitudinal panel direction, both are oblique relative to the panel front surface. Examples of this feature are visible in figures 3C and 3F. In an embodiment, a part of the panel peripheral surface 12 that is oblique relative to the panel front surface extends either along or transverse to the longitudinal panel direction. Examples of this feature are visible in all of figures 3A-3I except figures 3C and 3F.

[0073] The panels of figures 3A and 3B may be preferred, in view of ease of manufacturing. Additionally, or alternatively, the panels of figures 3A and 3B may be preferred in view of enabling a peripheral gap in between peripheral side surfaces that are at substantially right angles to the panel front surfaces in one direction and a peripheral gap between peripheral side surfaces that are oblique relatively to the panel front surfaces in another direction that is transverse to said one direction. As illustrated in figures 3A-3I, the panel bodies of the plurality of panels may each have four corners. As shown in figures 3D-3I, the panel peripheral surface of the individual panels may be, relative to the panel front surface, oblique along part of the panel peripheral surface and at a substantially right angle at the corners of the panel peripheral surface. As shown in figure 3G, in between one pair of neighbouring corners the panel peripheral surface may be partly oblique relative to the panel front surface. As shown in each of figures 3D, 3E, 3F, 3H, and 3I, in between two pairs of neighbouring corners the panel peripheral surface may be partly oblique relative to the panel front surface. Corners may be considered to be neighbouring if, along the panel peripheral surface, no other corner is in between the neighbouring corners.

[0074] One or more of the individual panels described with reference to figures 3A-3I, or the mirror images thereof, may be applied in a method, a use, a panel or an assembly disclosed herein. The individuals panels described with reference to figures 3A-3I, and the mirror images thereof, may each be applied in the orientation shown, or in a rotated orientation. For example, when covering at least part of a wall, the individual panels of one or more of figures 3A-3I, and / or a mirror image thereof, may be rotated 90 degrees relative to the orientation shown in figures 3A-3I. In the embodiments of figure 2A and 2B, the method includes, by means of the plurality of panels 2, realising absorption of low-frequency acoustic noise. Such low-frequency acoustic noise may be generated outside of the building and may have propagated towards the wall 4. The acoustic noise is schematically indicated in figures 2A, 2B, and 4 by means of arrows 18. The low-frequency acoustic noise may propagate towards and into the wall gap via two different paths. As indicated in figure 4, a first path towards and into the wall gap 16 is through the panel body 6, indicated in figure 4 by straight arrows 18. A second path towards and into the wall gap is through the peripheral gap, indicated in figure 4 through curved arrows 18.

[0075] Figure 4 illustrates that parts of a wave of low-frequency acoustic noise that propagates towards and into the wall gap via the panel body (along the first path), will show a phase difference at a position in the wall gap compared to another part of said wave of low-frequency acoustic noise that reaches said position in the wall gap 16 via the peripheral gap (along the second path). Said phase difference may be relatively large for low-frequency acoustic noise that propagates through a central part 22 of the panel body 6 towards and into the wall gap 16. Said phase difference may be relatively small for low-frequency acoustic noise that propagates through an edge part 24 of the panel body 6 towards into the wall gap 16.

[0076] Without intending to be bound by theory, cancellation of low-frequency acoustic noise may be achieved that reaches the wall gap via different paths. Alternatively, or additionally, the low-frequency acoustic noise 18 that propagated, through the peripheral gap 14 and / or through the panel body 6, into the wall gap 16, may at least partly be dissipated. Such dissipation may in particular take place in the peripheral gap. All together, the absorption may be understood to result from a complex interaction between low-frequency acoustic waves in the wall gap and / or in the peripheral gap, whose effects are difficult to predict in advance. It may be clear however, that a peripheral gap that is at least partly open is beneficial for realising the absorption, while it can be considered counter-intuitive to leave open at least part of the peripheral gap when covering the at least part of the wall.

[0077] Figures 5A and 5B show results of an absorption spectrum obtained in five experiments respectively of three numerical simulations. Figures 5A and 5B show, along the vertical axis, the absorption coefficient α S of a plurality of panels that cover a part of a floor wall. The absorption coefficient α S is shown as a function of frequency F (measured in Hertz), which is along the horizontal axis in figures 5A and 5B. In the experiments of figure 5A, the absorption coefficient is determined in a reverberation room as a function of frequency, using different panelling designs. In the experiments, a plurality of panels is positioned along part of a bottom wall of the reverberation room. The plurality of panels thus cover a part of the bottom wall of the reverberation room. The absorption coefficient α S can be determined by measuring an acoustic response in the reverberation room with the panels covering part of the bottom wall, relative to the acoustic response in the reverberation room without the panels being positioned therein. In the experiments of Fig. 5B, the absorption coefficient is determined by means of numerical simulation.

[0078] Methods for determining the absorption coefficient are known as such to the skilled person. Preferably, the method based on ISO standard NF EN ISO 354 (2004) is used, optionally in combination with ISO standard 9613-1:1993(EN). The methods described in said standards are known as such to the skilled person and are based on generally known and accepted methods. According to the first of said standards, the absorption coefficient α S is determined by calculating an equivalent absorption area A T and dividing it by the frontal surface area of the engineering model. The equivalent absorption area A T depends on the reverberation time T 1 and the sound velocity c 1 in an empty room, and on the reverberation time T 2 and the velocity of sound c 2 in a room with a plurality of panels covering part of the floor of the reverberation room. The reverberation time may be defined as the time that would be required for a measured sound pressure level to decrease by 60 dB after the sound source that is used for generating sound for the measurements in the reverberation room has stopped. The equivalent absorption area A T also depends on the volume V of the reverberation room. The dependency of the equivalent absorption area A T on said variables is determined by: A T = 55,3 V 1 c 2 T 2 − 1 c 1 T 1 − 4 V m 2 − m 1 wherein the following temperature-dependency of the sound velocity c on temperature is used: c = 331 + 0,6 t , wherein t indicates temperature in degrees Celsius at the moment of measuring and should be in between 15 degrees Celsius and 30 degrees Celsius. The absorption coefficient α S equals the equivalent absorption area A T divided by the frontal surface area. The equivalent absorption area A T and the absorption coefficient α S may be determined for frequencies that subsequently increase with one-third of an octave.

[0079] If, in the reverberation room, the air temperature, ambient atmospheric pressure, and / or concentration of water vapour in the air during the measurement in the empty reverberation room differ from respectively the air temperature, ambient atmospheric pressure and / or concentration of water vapour in the air during the measurement in the reverberation room with a plurality of panels covering part the floor wall of the reverberation room, a correction can be applied to the equivalent absorption area A T . As expressed in the above formula, the correction equals -4V(m 2 - m 1 ), wherein m 1 and m 2 are the attenuation coefficients during measuring of the reverberation time in the empty room respectively in the room wherein the plurality of panels covers part of the floor of the reverberation room. The correction can be relatively small. The values of m 1 and m 2 can be inferred from the ISO standard 9613-1 : 1993(EN). However, preferably, the temperature, ambient atmospheric pressure and concentration of water vapour are the same during both measurements, so that the attenuation coefficients m 1 and m 2 are about the same and the correction is negligible.

[0080] The absorption coefficient α S that is determined in the experiments in the reverberation room in this way, can be considered to be indicative for absorption of low-frequency acoustic energy in practical situations. Hence, the absorption properties of a plurality of panels as described in the present disclosure, may be determined in a reverberation room according to standardised methods such as ISO standard NF EN ISO 354 (2004) and optionally ISO standard 9613-1 : 1993(EN), as described herein. For such determinations, engineering models can be used that resemble the practical situation. Preferably, in an engineering model, panels of a similar type, composition, and dimensions are used as in the practical situation that is to be assessed. Preferably, in an engineering model, a similar peripheral gap and wall gap is used as in the practical situation that is to be assessed. An engineering model may e.g. resemble, or be similar to, at least a part of a facade that includes a plurality of panels and that is to be assessed.

[0081] Figure 5A shows results of five experiments labelled E1, E2, E3, E4, and E5. In each of the experiments, a different type of panel or panelling design is tested. Panels of a first type, which are marketed under the trade name Equitone@ Picture, were used in experiment E1. The panels of this first type have a panel thickness Y of 8 millimetre and weigh 15,6 kilogram per square metre. Panels of the first type have a planar front surface that is formed by a UV-cured coating. Panels of a second type, which are marketed under the name Equitone ®< Linea, were used in experiment E2. Panels of this second type have a thickness that varies between 8 and 10 millimetre and weigh 16,3 kilogram per square metre. The panels of the second type are uncoated, so that the panel front surface is formed by the panel body. The variation in thickness of the panels of the second type is caused by a structure of straight and parallel channels in the panel front surface with a depth of about 2 millimetre that extend along the panel front surface at a regular distance from each other.

[0082] Panels of a third type, which are marketed under the name Equitone@ Lunara, were used in experiment E3. The panels of this third type have a thickness of approximately 10 millimetre and weigh about 18,5 kilogram per square metre. The panels of the third type are uncoated, so that the panel front surface is formed by the panel body. At the panel front surface a quasi-random pattern of surface variations is provided. Panels of a fourth type, which are marketed under the name Equitone@ Tectiva, were used in experiment E4 and E5. Panels of the fourth type have a thickness of about 8 millimetre and weigh about 14,6 kilogram per square metre (in experiment E4) or about 14,4 kilogram per square metre (in experiment E5). The panels of the fourth type are uncoated, so that the panel front surface is formed by the panel body. The panel front surface of the panels of the fourth type is planar and is sanded.

[0083] The four types of panels that were used in the experiments E1-E5, all have a body made of fibre cement material. They are commercially available and known as such to the skilled person. The panel bodies of these types of panels are porous and may typically have a porosity in a range from about 13 percent to about 25 percent, in particular in a range from about 15 percent to about 22 percent. The Equitone@ Lunara, Linea and Tectiva panels are based on autoclave-cured technology and have essentially corresponding material constitution. These panels are without surface coating. The Equitone@ Picture panel is a coated panel of which the fiber cement material is manufactured in air-cured technology. All Equitone@ panels are commercially available from Eternit NV, Kapelle-op-den-Bos, Belgium.

[0084] Figures 6A and 6B schematically show a transparent top view of the two engineering models 28 with mutually differing panelling designs that were used in the experiments. Figure 6C shows a cross section C-C' indicated in figure 6A. The panelling of figure 6A is provided with nine rectangular individual panels. In the view of figure 6A, these panels have a panel length that extends in the horizontal direction and a panel width that extends in the vertical direction. In the panelling design shown in figure 6A, the panel width is about 989 millimetres and the panel length is about 1189 millimetre. The panelling of figure 6B is provided with six rectangular individual panels 2. In the view of figure 6B, the panels have a panel length that extends in the vertical direction and a panel width that extends in the horizontal direction. In the panelling design shown in figure 6B, the panel width is about 1189 millimetre and the panel length is about 1488 millimetre. In the panelling design of the engineering model of figure 6A, the peripheral gap is about 8 millimetres. In the panelling design of the engineering model of figure 6B, the peripheral gap is about 12 millimetres. An engineering model having the panelling design of figure 6A was used in experiments E1, E2, E3, and E4. An engineering model having the panelling design of figure 6B was used in experiment E5.

[0085] For both panelling designs shown in figures 6A and 6B, an aperture ratio may be defined, for the plurality of panels that form a façade. The aperture ratio of the plurality of panels, i.e. of the facade, may be defined as the ratio of an area, measured along the panel front surfaces, of an open part of the façade and a closed part of the facade. Thus, the aperture ratio may equal the area, measured in a direction along the panel front surface, of the open parts of the façade (formed by the open parts of the peripheral gap at the front surface) divided by the closed area of the facade (formed by the sum of the area of the panel front surfaces and the area of the closed parts of the peripheral gap at the front surfaces). In the panelling design of figures 6A and 6B, the aperture ratio was within a range from 0,002 to 0,007. In a practical embodiment, the facade may have an aperture ratio of at most 0,02, preferably at most 0,01, more preferably at most 0,005.

[0086] In both engineering models 28, below the panels 2, a width W of the wall gap 16 (indicated in figure 2) of 200 millimetre is provided (indicated in figure 6C). A layer of rock wool that can dampen low-frequency acoustic noise, is provided in the wall gap. Thus, part of the wall gap 16 is filled with a layer of rock wool 30, having a thickness of about 150 millimetres. In view of the width of the wall gap, in this embodiment, a majority of the wall gap is filled with rock wool. On top of the layer of rock wool, wooden bars 32 are provided. The wooden bars have a length of about 3000 millimetres, a width of about 145 millimetres and a thickness of about 45 millimetres. The panels 2 are attached to these bars with screws 34. A layer of felt 36 is provided in between the bars 32 and the panels 2. The layer of felt has a width of about 100 millimetres. The wooden bars 32 may resemble the frame with which the panels may be attached to the wall. A frontal surface 33 of the engineering model was 10,8 square metres. The frontal surface may be formed by the panel front surfaces, the peripheral gap (whether closed or open), and an edge formed by a border element 38.

[0087] In the panelling designs shown in figures 6A and 6B, a planar panel dimension P of about 495 millimetres respectively about 744 millimetres can be recognised. This planar panel dimension may be the shortest distance from a central panel body part 22 to a position 42 on the panel peripheral surface where the peripheral gap is open. In this embodiment, and in other embodiments, the central panel body part 22 may e.g. coincide with a midpoint of the panel body 6, in particular with an imaginary axis that extends through said midpoint in a direction perpendicular to the panel front surface. The midpoint may e.g. be formed by the centre of gravity of the panel when the panel front surface is in a substantially horizontal position. In the design of figure 6A, the planar panel dimension P is half of a width of a panel. In the panelling design of figure 6B, the planar panel dimension P is half of a length of a panel. The border element 38 is provided around the panelling, which may be made of a wooden plank. In both designs, the outer dimensions of the panelling design are 3000 millimetres by 3600 millimetres. As will be clear from figures 6A-6C, the parts of the peripheral gap 14 that are vertical in figures 6A and 6B, are blocked (i.e. closed) by means of the bars 32 in combination with the layer of felt 36. At the border element 38, aluminium tape 40 is applied to obtain a sufficient acoustic isolation between the border element 38 and the floor wall 4, and between the border element 38 and the panels 2 along the border element 38. The tape 40 is drawn in figure 6C but is not visible in figures 6A and 6B.

[0088] The absorption coefficient of the engineering panels was determined based on the method according to ISO standard NF EN ISO 354 (2004) and ISO standard 9613-1:1993(EN), which is described herein above. The experiments were carried out in a reverberation room, having walls with relatively hard surfaces that may be formed by concrete. The reverberation room has a volume of 252 cubic metre and is provided with twelve diffusers. It is equipped with sensors for measuring temperature, relative humidity and atmospheric pressure. In all experiments, the atmospheric pressure was 101,4 kilopascal, the temperature was about 19 degrees Celsius in experiments E1 and E5 and about 19,5 degrees Celsius in experiments E2, E3, and E4, and the relative humidity was about 64 percent, 65 percent, 66 percent, 68 percent, and 69 percent in respectively experiments E1, E2, E3, E4, and E5. In the reference experiments with an empty reverberation room, the temperature was about 19 degrees Celsius, the relative humidity was about 60 percent, and the atmospheric pressure was about 101,4 kilopascal.

[0089] Going back to the experimental results of figure 5A, these firstly indicate that a significant absorption of low-frequency acoustic noise can be realised. At a main absorption frequency (or, in other words, a frequency of the low-frequency acoustic noise at which a maximum of the absorption of low-frequency acoustic noise is reached), the absorption coefficient can be reduced at least 20 percent, at least 30 percent, or at least 40 percent. It may be expected that by further optimization of the planar panel dimension, the peripheral gap, and / or the wall gap, possibly in combination with other properties such as surface properties of the panels and / or a porosity of the panel bodies, the absorption may be further improved. Preferably, the absorption coefficient is at least 50 percent or at least 60 percent, at a main absorption frequency of the low-frequency acoustic noise.

[0090] Comparing experiments E4 and E5, which were carried out with panels of one and the same type, indicates how the open peripheral gap can be relevant. In the experiment E4 wherein the panelling design of figure 6A is applied, the total length of open peripheral gap was about twice as large as in the experiment E5, wherein the panelling design of figure 6B was applied. This was the consequence of the ordering of the panels. In experiment E4 open peripheral gaps were present on opposite sides of a single panel. In other words, there was an open peripheral gap both between a first and a second row of panels and between the second row and a third row of panels. In experiment E5, there was merely a first and a second row of panels and hence merely a single open peripheral gap between those rows. The peripheral gap width was also different between experiment E4 and E5. The experimental results indicate that the absorption coefficient α S in experiment E4 can be about twice as large as the absorption coefficient α S in the experiment E5, for frequencies in a range from about 50 Hertz to about 100 Hertz. In view of the difference in absorption between experiments E4 and E5, preferably an aperture ratio of the facade formed by the plurality of panels, is at least 0,003 or is at least 0,004. Preferably, for the individual panels, a minimum distance between open parts of the peripheral gap that are at opposite sides of the panel body, and that can be connected by a straight line that goes through the central part of the panel body, is at most 1,3 metre. For sake of clarity, it is observed that the ordering of the panels was the same in experiments E1 to E3 as in E4.

[0091] Figure 5B shows the absorption coefficient α S of a plurality of panels that cover a wall, as determined in three different numerical simulations S1, S2, and S3. The numerical simulations were carried out using a numerical Transfer Matrix Method. Commercially available software packages are available for carrying out numerical simulations of this type, which is known as such to the skilled person. The numerical simulations take into account, among other variables, the aperture ratio of the engineering models and properties of materials used in the engineering models. Although carrying out the numerical simulations requires making assumptions and approximations, the numerical simulations were found to roughly confirm the experimental results (as visible in figures 5A and 5B).

[0092] In the numerical simulations S1 and S2, a peripheral gap width of 8 millimetre respectively 10 millimetre was implemented. The peripheral gap width was substantially constant along a propagation direction of the low-frequency acoustic noise through the peripheral gap towards the wall. In the numerical simulation S3, a peripheral gap width at the panel front surface of 8 millimetre was implemented. This peripheral gap width increased along the propagation direction of said low-frequency acoustic noise through the peripheral gap towards the wall. An angle β (indicated in figure 4) of 45 degrees was implemented in the model used for the numerical simulation S3. In the numerical simulations S1. S2, and S3, values for the materials properties and dimensions of the layers were used that are representative for the engineering models 28 described with reference to figures 6A-6C.

[0093] The numerical simulations S1 and S2 thus indicate that a wider peripheral gap of 10 millimetres instead of 8 millimetres, increased the absorption. The numerical simulations S1 and S3 indicate that a panel peripheral surface that is oblique (or, in other words, inclined) relative to the panel front surface so that the peripheral gap becomes wider along a propagation direction of the low-frequency acoustic noise through the peripheral gap towards the wall, also increases the absorption. The results of the experiments and numerical simulations indicate, more in general, that a significant absorption of low-frequency acoustic noise may be realised in practice by means of the panels in combination with the peripheral gap and the wall gap. Such absorption could moreover, optionally, lead to a reduction of the transmission of the low-frequency acoustic noise into a building and / or to a significant reduction of the reflection of the low-frequency acoustic noise in a direction away from the wall. After all, as a result of the absorption, less acoustic energy of the low-frequency acoustic noise could be available for such transmission and / or reflection. Figures 5A and 5B show that at a main absorption frequency in the low-frequency range below 100 Hertz, a maximum of the absorption can be reached. Possibly, at a similar frequency, a maximum in the reduction of the reflection and / or transmission can be reached.

[0094] More specifically, the experiments and numerical simulations that are presented with reference to figures 5A-6C, illustrate that the planar panel dimension P, the peripheral gap 14 and the wall gap 16 can be arranged so that a significant amount of absorption of low-frequency acoustic noise can be reached at or around a main absorption frequency. In most of the experiments and numerical simulations that were carried out, said main absorption frequency is about 63 Hertz and the absorption at the main absorption frequency is at least about 30 percent. However, in practical situations, the panelling design may be different, so that another main absorption frequency and / or another absorption level may be realised. Preferably, the main absorption frequency is at least 20 Hertz and / or is at most 100 Hertz, more preferably is at least 40 Hertz and / or is at most 90 Hertz. In particular, the main absorption frequency may be in a range from 50 Hertz to 80 Hertz, for example in a range from 60 Hertz to 70 Hertz. The planar panel dimension may optionally be at least 20 Hertz metre divided by said main absorption frequency and / or may optionally be at most 160 Hertz metre divided by said main absorption frequency.

[0095] Figures 7A and 7B schematically show a plurality of panels that may be used in a method according to one or more embodiments discussed with reference to figures 1A-6C. Figure 7A shows the panels 2 in a back side view, when being positioned along a vertical wall (the vertical wall is not drawn in figure 7A). Figure 7B shows, in a top view of a horizontal cross section through the vertical wall 4, the plurality of panels 2 in an assembly with the vertical wall 4 when being positioned along the wall. The plurality of panels 2 shown in figures 7A and 7B may also be used in other embodiments of the invention. As shown in figures 7A and 7B, the panel back surfaces 10 of the plurality of panels 2 may be provided with a ridge 44. The positioning of the plurality of panels along the wall, may include positioning the ridges 44 against the wall. Each ridge 44 partitions, alone or in combination with other ridges, the wall gap 16 in order to create at least two cavities 46.1, 46.2 in the wall gap that are in fluid communication with the peripheral gap 14. As a result, the low-frequency acoustic noise can propagate through the peripheral gap 14 into the cavity 46.1 or the cavity 46.2 in the wall gap.

[0096] As indicated in figures 7A and 7B, the at least two cavities may have volumes that differ from each other. As a result, acoustic properties of one of the at least two cavities can be different from acoustic properties of another one of the at least two cavities. In particular, a resonance frequency of one of the at least two cavities can be different from a resonance frequency of another one of the at least two cavities. By means of the ridge 44, the absorption of low-frequency acoustic noise by means of the panels 2 may be further adjusted. In particular, the ridge may enable a more even spectrum of the absorption coefficient α S , at least at frequencies in between 20 Hertz and 100 Hertz. In the embodiment of figures 7A and 7B, the ridge is substantially straight. However, in other embodiments the ridge may be curved and / or may have one or more branches.

[0097] The ridges 44 may be formed by a frame that is attached to the wall and to which the plurality of panels is attached. Thus, in an embodiment, the frame may be designed for partitioning the wall gap for forming a plurality of cavities 46.1, 46.2. In another embodiment, the ridges may be integral to the panels. For example, the ridges may be attached to the panels before the panels are attached to the frame and / or to the wall. In another embodiment, part of the ridges 44 may be integral to the panels and part of the ridges are formed by the frame. In such embodiments, a part of the back surfaces of the plurality of panels may contact the wall and another part of the back surfaces of the plurality of panels may be spaced apart from the wall. More in general, the panel back surfaces of the plurality of panels may be completely or may be partly spaced apart from the wall, for having the wall gap between the panel bodies and the wall.

[0098] Figure 8 illustrates a method in a further embodiment of the invention. Figure 8 schematically shows, in a top view, a plurality of buildings each having a wall that is at least partly covered by means of a plurality of panels 2. The wall 4.1 at least partly covered by a plurality of panels 2 of a building 50.1, faces another wall 4.2 that is at least partly covered by a plurality of panels 2. The other wall 4.2 is part of another building 50.2. As a result of the walls 4.1, 4.2 of the two buildings 50.1, 50.2 facing each other, low-frequency acoustic noise that is reflected from the wall 4.1 can propagate towards said other wall 4.2. Two buildings may be regarded to face each other if a ray of acoustic noise that is reflected with an angle of 45 degrees relative to the panel front surface 8 of a panel on one of the two buildings, can reach the other one of the two buildings without further reflections while propagating along a straight line.

[0099] As illustrated in figure 8, the panel back surfaces 10 of the panels 2 may be spaced apart from the wall 4.1. As a result, the assembly of the wall 4.1 and the plurality of panels 2 that at least partly cover the wall 4.1, may define a wall gap 16 between the panel bodies 6 and the wall 4.1. Figure 8 shows the same for the assembly of the wall 4.2 and the panels 2 that at least partly cover the wall 4.2. Figure 8 also schematically illustrates that panel bodies 6 of the plurality of panels are spaced apart from each other. As a result, the plurality of panels 2 that at least partly cover a wall of one of the buildings, has a peripheral gap 14 between the panel bodies 6. As described herein, by means of the positioning of the panels and the dimensioning of the panels, the wall gap, and the peripheral gap, absorption of low-frequency acoustic noise can be realised. If low-frequency acoustic noise that reflected from the building 50.1 is absorbed by means of a plurality of panels 2 on said other building, reducing the amplitude of the low-frequency acoustic noise in an environment of the building 50.1 may be realised effectively.

[0100] As schematically indicated in figure 8, the planar panel dimension, the peripheral gap and / or the wall gap of the plurality of panels positioned along the wall may be different for different buildings. For example, the planar panel dimension, the peripheral gap and / or the wall gap of the plurality of panels positioned along the wall 4.1 may be different from the planar panel dimension, the peripheral gap and / or the wall gap of the plurality of panels along the other wall 4.2. As a result, a main absorption frequency of the low-frequency acoustic noise at which a maximum in the absorption is realised by means of the panels covering the wall 4.1, may be different from another main absorption frequency of low-frequency acoustic noise at which a maximum in the absorption is realised by means of the panels covering the other wall 4.2. In this way, the low-frequency acoustic noise may be absorbed more evenly along a wider range of frequencies (i.e., the absorption spectrum may be broader).

[0101] In the example of figure 8, the wall 4.1 of the building 50.1 and the other wall 4.2 of the other building 50.2, are at opposite sides of a street 52. The low-frequency acoustic noise may e.g. be generated by traffic that propagates on the street 52. Thus, as along the street 52 a plurality of buildings may be provided, one or more other buildings may be present in an environment of each of the buildings shown. The method may include covering at least a part of a wall that faces the street 52 of each of the provided buildings, using a method according to an embodiment of the invention. As a result, low-frequency acoustic noise that is reflected from the wall of one building of the plurality of buildings can propagate towards the wall of another building of the plurality of buildings. By realising absorption by means of the panels at main absorption frequencies that are different for each of the buildings of the plurality of buildings, low-frequency acoustic noise in an environment of the buildings may be absorbed effectively over a wider frequency range.

[0102] The invention is not limited to the embodiments, variations, examples, aspects, features etc. as described herein. For example, the invention may be applied to low-frequency acoustic noise with a frequency of at most 200 Hertz, and optionally of at least 20 Hertz. Optionally, the main absorption frequency is at least 20 Hertz and / or at most 200 Hertz. In an embodiment, the panel and / or the panel body may have a thickness of at least 12 millimetres. An oblique part of a panel peripheral surface referred to herein is not necessarily oblique over the whole distance from panel front surface to panel back surface. Instead, optionally, an oblique part of a panel peripheral surface may e.g. be rounded near the panel front surface or the panel back surface, or may have a substantially right angle to the panel front surface at positions near the panel front surface. In this way, the panel may be less vulnerable to damage. An oblique part of the panel peripheral surface does not have to be flat. It optionally may contain one or more ridges or may contain a stepped profile.

[0103] The walls referred to herein may fall into a broad range of different wall types. For example, one or more of the walls may be vertical, horizontal, and / or inclined relative to the horizontal direction. One or more of the walls may be continuous or may be discontinuous. One or more of the walls may be provided with one or more openings and / or may include two or more wall parts that may be separate. One or more of the walls may include concrete and / or bricks. Alternatively, or additionally, the one or more of the walls may include wood and / or one or more types of wall board. Similarly, the term building may refer a wide range of building types, such as residential buildings, office buildings, hospital building, and / or factory buildings, but also other build structures that include one or more walls.

[0104] Although in the present disclosure the invention is often described with reference to a method of covering the wall, the invention can also be described as a use of a plurality of panels for covering the wall or as an assembly of a plurality of panels and the wall. The embodiments, examples, and features of said method described herein may also be applied in combination with said use or said assembly, or in combination with an individual panel. For example, a frame for attaching the panels to a support structure that is attached to a wall, may be formed by wooden bars like the wooden bars of the engineering models shown in figures 6A and 6B. In addition, the present disclosure also relates to each individual panel disclosed herein and the mirror image thereof, whether or not described as one of a plurality of panels. Such panels may be used in an orientation shown or described, or in a rotated orientation. Such rotation may e.g. be 90 degrees, so that vertical and horizontal directions of the panels are reversed relative to an orientation as described and / or drawn.

Examples

Embodiment Construction

[0050]The present disclosure relates to a method of covering at least part of a wall of a building by means of a plurality of panels, directed to the purpose of absorbing low-frequency acoustic noise. Such noise may e.g. be generated in, or may propagate into, an environment of the building and propagate towards the wall. The panels may be of various shape and composition. For example, the panels may each have a panel body that is made of fibre cement material, or at least includes 50 weight percent fibre cement material. Fibre cement material is a material that includes cement and fibers, and that thus may be regarded as a composite material. The fibers may be cellulose fibers and / or synthetic fibers. The manufacture of fibre cement material is known as such. Panels with another composition may be used alternatively or additionally to panels that include a fibre cement material. Preferably, the body of the panels includes a porous material. The porous material may e.g. have a poros...

Claims

1. Method of covering at least part of a wall of a building by means of a plurality of panels, wherein individual panels of said plurality of panels each include a panel body and have a panel front surface, a panel back surface, and a panel peripheral surface, the method including: - positioning the plurality of panels along the wall so that the panel front surfaces face away from the wall, wherein, after the positioning, the panel bodies of the plurality of panels are spaced apart from each other for having a peripheral gap between the panel bodies, and wherein, after the positioning, the panel back surfaces of the plurality of panels are at least partly spaced apart from the wall for having a wall gap between the panel bodies and the wall; and - realising in the wall gap and / or the peripheral gap, by means of the positioning of the plurality of panels, absorption of low-frequency acoustic noise that is generated outside of the building and that propagated towards the wall to reach the wall gap and / or the peripheral gap.

2. Method according to claim 1, wherein the panel body of each of the individual panels has a planar panel dimension in a direction along the panel front surface of the individual panel, wherein the method includes: - arranging the planar panel dimension of the plurality of panels, the peripheral gap, and the wall gap so that low-frequency acoustic noise that propagated towards the wall to reach the wall gap and / or the peripheral gap, at least partly cancels out and / or dissipates in the wall gap and / or the peripheral gap, so that the absorption of low-frequency acoustic noise is realised.

3. Method according to claim 2, wherein the panel bodies of the plurality of panels each include a central panel body part, wherein the planar panel dimension extends from the central panel body part to the panel peripheral surface, the method including: - arranging the planar panel dimension of the plurality of panels, the peripheral gap, and the wall gap so that a maximum of the absorption of low-frequency acoustic noise is realised at a main absorption frequency of the low-frequency acoustic noise, wherein the planar panel dimension is at least 20 Hertz metre divided by said main absorption frequency and is at most 160 Hertz metre divided by said main absorption frequency.

4. Method according to one of claims 1-3, wherein the panel body of each of the individual panels has a perimeter that is defined by the panel peripheral surface of the panel body, wherein the peripheral gap is open along the perimeter of at least one of the individual panels, so that the low-frequency acoustic noise can propagate through the open peripheral gap.

5. Method according to one of claims 1-4, wherein the peripheral gap extends in a longitudinal peripheral gap direction in between at least two panel bodies of said plurality of panels, wherein the peripheral gap has a peripheral gap width in a direction that is transverse to said longitudinal peripheral gap direction and that is directed from one of the at least two panel bodies to another one of the at least two panel bodies, wherein, along at least part of the peripheral gap, the peripheral gap width increases along a propagation direction of said low-frequency acoustic noise through the peripheral gap towards the wall.

6. Method according to one of claims 1-5, wherein the panel peripheral surface of at least one of the individual panels is, along at least part of the peripheral gap, oblique relative to the panel front surface, wherein, along the at least part of the peripheral gap, an angle between the panel peripheral surface and the panel front surface is in a range from 20 degrees to 70 degrees.

7. Method according to one of claims 1-6 that includes providing, in the wall gap, a damping material that is arranged for damping the low-frequency acoustic noise.

8. Method according to one of claims 1-7, wherein the panel back surface of at least one of the individual panels is provided with a ridge, wherein, after the positioning of the plurality of panels, the at least one ridge partitions the wall gap in order to create at least two cavities in the wall gap that are in fluid communication with the peripheral gap so that the low-frequency acoustic noise can propagate through the peripheral gap into the cavities in the wall gap.

9. Method according to one of claims 1-8, wherein the wall faces another wall that is covered by means of a method according to one of claims 1-9, so that low-frequency acoustic noise that is reflected from the wall can propagate towards said other wall.

10. Method according to claim 9, wherein the planar panel dimension, the peripheral gap and / or the wall gap of the plurality of panels positioned along the wall is different from the planar panel dimension, the peripheral gap and / or the wall gap of the plurality of panels along the other wall.

11. Method according to claim 9 or 10, wherein a frequency of low-frequency acoustic noise at which a maximum in the absorption is reached by means of the panels covering the wall, is different from another frequency of low-frequency acoustic noise at which a maximum in the absorption is reached by means of the panels covering the other wall.

12. Use of a plurality of panels for covering at least part of a wall of a building, wherein individual panels of said plurality of panels each include a panel body and have a panel front surface, a panel back surface, and a panel peripheral surface, the use including: - positioning the plurality of panels along the wall so that the panel front surfaces face away from the wall, wherein, after the positioning, the panel bodies of the plurality of panels are spaced apart from each other for having a peripheral gap between the panel bodies, and wherein, after the positioning, the panel back surfaces of the plurality of panels are at least partly spaced apart from the wall for having a wall gap between the panel bodies and the wall; and - realising in the wall gap and / or the peripheral gap, by means of the positioning of the plurality of panels, absorption of low-frequency acoustic noise that is generated outside of the building and that propagated towards the wall to reach the wall gap and / or the peripheral gap.

13. Panel that is arranged for covering at least part of a wall of a building, wherein the panel includes a panel body and has a panel front surface, a panel back surface, and a panel peripheral surface, wherein the panel is arranged for being positioned along the wall so that the panel front surface faces away from the wall and at least part of the panel back surface is spaced apart from the wall, wherein at least part of the panel peripheral surface is oblique relative to the panel front surface, wherein an angle between the panel peripheral surface and the panel front surface is in a range from 20 degrees to 70 degrees.

14. Assembly of a plurality of panels and a wall of a building, wherein the plurality of panels covers at least part of the wall of the building, wherein individual panels of said plurality of panels each include a panel body and have a panel front surface, a panel back surface, and a panel peripheral surface, wherein the plurality of panels is positioned along the wall so that the panel front surfaces face away from the wall, wherein the panel bodies of the plurality of panels are spaced apart from each other so that the plurality of panels has a peripheral gap between the panel bodies, and wherein the panel back surfaces of the plurality of panels are at least partly spaced apart from the wall so that the assembly defines a wall gap between the panel bodies and the wall, wherein the plurality of panels is arranged and positioned for realising, in the wall gap and / or the peripheral gap, absorption of low-frequency acoustic noise that is generated outside of the building and that propagated towards the wall to reach the wall gap and / or the peripheral gap.

15. Assembly according to claim 14 that is used in a method according to one of claims 1-11, that is used in a use according to claim 12, or that includes one or more panels according to claim 13.

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