Sound absorber

Abstract

A sound-absorbing structure, comprising: a plurality of sheet material pieces, optionally made of thermoplastic sheet material or optionally made of a metal sheet material, such as aluminium, wherein the sheet material pieces are stacked, rolled or folded such that each piece comprises superimposed parts and / or parts of different sheet material pieces are arranged one above the other, wherein at least some of the superimposed parts and at least some of the parts of different material pieces do not lie directly adjacent to each other, but have small gaps between them for the entrance of sound from the surrounding, and wherein at least some and preferably all sheet material pieces have a crinkled or wrinkled structure.

Description

[0001] The present disclosure relates to a sound absorber and a sound absorbing structure.

[0002] Acoustic materials are usually used for noise reduction in various environments, including architectural spaces, machinery, and urban settings. The demand for noise control solutions has significantly increased due to the growing awareness of the impact of noise pollution on human health and well-being. The importance of acoustic comfort in living and working spaces, as well as in the operation of machinery, has become a critical factor in the design of new technologies and infrastructure.

[0003] Traditional approaches to noise reduction involve the use of materials specifically designed for either sound insulation or sound absorption. Sound insulation materials rely on mass and rigidity to block or reduce the transmission of sound from one space to another, whereas sound absorption materials focus on diminishing sound reflections within an enclosed area by converting sound energy into heat, thus reducing the overall noise level.

[0004] Porous materials, a common choice for sound absorption, are typically categorized into three main groups: foams, fibers, and granules. These materials are effective because they allow sound waves to enter their porous structures, where the energy is dissipated through friction and structural vibration. This dissipation occurs across a wide frequency range, making porous materials particularly valuable for various acoustic applications.

[0005] Despite the effectiveness of traditional porous materials, it is an objection of the present invention to provide an improved sound absorber, which can offer an improved performance, sustainability, and versatility.

[0006] The object is satisfied by a sound absorber as claimed in claim 1. Preferred embodiments are described in the dependent claims.

[0007] In an aspect, a sound absorbing structure (also called sound absorbing apparatus) comprises a plurality of sheet material pieces, optionally made of thermoplastic sheet material, wherein the sheet material pieces are stacked, rolled or folded such that each piece comprises superimposed parts and / or parts of different sheet material pieces are arranged one above the other, wherein at least some of the superimposed parts and at least some of the parts of different material pieces do not lie directly adjacent to each other, but have gaps, in particular small gaps, between them for the entrance of sound from the surrounding, and wherein at least some material pieces and preferably each material piece of the plurality of sheet material pieces has a crinkled or wrinkled structure.

[0008] The gaps may be present in between superimposed parts of the same sheet material piece, in particular when the material piece is rolled or folded, so that different portions of the same sheet material piece are arranged on top of each other and are thus superimposed. The gaps may also be present between different sheet material pieces, for example when they are arranged adjacent to each other in a structure or when different sheet material pieces are stacked. The gaps may be formed arbitrarily and randomly due to rolling, folding and / or stacking the sheet material pieces with only a low force and due to the crinkled or wrinkled structure or texture of the sheet material pieces which may ensure that at least small gaps are present between adjacent, neighbouring portions or layers of the same or different sheet material pieces.

[0009] The sheet material pieces may be arranged such that the gaps have openings at least on one side of the sheet material pieces, so that external sound can enter the gaps for sound reduction and / or absorption.

[0010] In some embodiments, the plurality of the sheet material pieces is arranged in a defined structure. For example, the sheet material pieces can be arranged such that the gaps have openings to at least one side of the structure. For the intended use of the sound absorbing structure, it is then particularly useful to place this side such that the side faces the direction from where external sound is incident.

[0011] In some embodiments, at least some and preferably all the sheet material pieces have serrations, in particular triangular serrations, at least on one edge. The serrations at least on one edge of the sheet material pieces help reducing and / or absorbing sound. The serrations may form serrated edges of the sheet material pieces. In particular, the serrations may extend over the full length of at least one egde of a sheet material piece.

[0012] In some embodiments, the sheet material pieces are arranged in a defined structure such that the edges with serrations lie on one side of the structure. Thus, the serrations are on one side of the structure, and they can thus face the direction of incoming sound during the intended use of the structure. Thus, during the intended use of the sound absorbing structure, the side of the structure where the serrations are arranged may be placed such that a direction of incoming sound hits at this side the structure.

[0013] In some embodiments, at least some of the gaps between material pieces are open to one side of the structure, in particular such that sound can enter the gaps on this side. The sound can thus enter the gaps.

[0014] In some embodiments, a rolled sheet material piece has a central axis around which the material piece is rolled.

[0015] In some embodiments, a folded material piece has a central axis extending along a folding edge of the sheet material piece.

[0016] In some embodiments, the plurality of sheet material pieces is arranged in a defined structure, which defines a main axis, and rolled or folded sheet material pieces are arranged such that the central axes of the sheet material pieces are at least approximately parallel to the main axis.

[0017] In some embodiments, the plurality of sheet material pieces is arranged in a defined structure, which defines a main axis, and rolled or folded sheet material pieces are arranged such that the central axes of the sheet material pieces are inclined to the main axis, at a maximum angle of no more than 60 degrees, preferably no more than 30 degrees, and more preferably no more than 15 degrees. Sheet material pieces which are arranged at different angles can be advantageous for absorbing sound at higher frequencies.

[0018] In some embodiments, the stacked sheet material pieces have a central plane which extends in parallel to the sheet plane of the sheet material pieces.

[0019] In some embodiments, the plurality of sheet material pieces is arranged in a defined structure, which defines a main plane, and the stacked material pieces are arranged such that the central planes of the sheet material pieces extend at least approximately parallel to the main plane.

[0020] In some embodiments, the plurality of sheet material pieces is arranged in a defined structure, which defines a main plane, and the stacked material pieces are arranged such that the central planes of the sheet material pieces are inclined to the main plane, at a maximum angle of no more than 60 degrees, preferably no more than 30 degrees, and more preferably no more than 15 degrees.

[0021] In some embodiments, in particular during the intended use of the sound absorbing structure, the sheet material pieces are arranged such that their main axes and / or their main planes are arranged at least approximately in parallel to a main direction of incoming sound.

[0022] In some embodiments, the gaps between different sheet material pieces or between parts of the same sheet material piece have a non-uniform width and / or are arbitrarily and randomly formed.

[0023] In some embodiments, a sound absorbing structure comprises at least one and preferably a plurality of material pieces, such as sheets, tapes, or membranes, for sound absorption, wherein each material piece consists of or comprises an elastic material, wherein at least some and preferably all of the material pieces have a lateral edge, wherein serrations, in particular triangular serrations, are arranged in the lateral edge of the respective sheet, wherein one or more material pieces are rolled up to form a roll and wherein a plurality of rolls is arranged such that that the lateral edges with the serrations are on the same side.

[0024] The invention also relates to the use of the described sound absorbing structure in an acoustic panel, sound absorption unit, or interior sound treatment installation.

[0025] In some embodiments, a sound absorber comprises a housing having an entrance for sound at least on one side and a sound absorbing structure as defined in embodiments of the sound absorbing structure, wherein the sheet material pieces are arranged in a defined structure such that a side of the structure, which is intended for sound absorption, is oriented towards the entrance of the housing.

[0026] In an aspect, a sound-absorbing structure comprises a porous body formed from a plurality of material pieces, such as pieces made of thermoplastic sheet material, wherein each material piece is rolled, folded, or crinkled to define an internal structure open to airflow, and the structure is configured such that incident sound enters and propagates in a direction substantially parallel to the orientation of the sheet material pieces.

[0027] In some embodiments, each sheet-like material piece is rolled, folded, or crinkled to define an internal structure open to airflow. Furthermore, a plurality of the material pieces may be arranged such that they form a structure which is open to airflow. The structure may serve as a sound absorber and sound may be able to enter and propagate in between the arrangement of rolled, folded, or crinkled material pieces such that the sound level is effectively reduced or absorbed.

[0028] In some embodiments, a porous body may be formed from a plurality of the material pieces.

[0029] In some embodiments, the material pieces are rolled into cylindrical elements and arranged in an array with their lateral edges oriented toward the sound source.

[0030] In some embodiments, a material piece may comprise or consist of a roll of thin, randomly pleated material, rolled with a small force.

[0031] In some embodiments, the thermoplastic material is a recycled polymer or plastic film, optionally sourced from reused packaging such as plastic bags.

[0032] In some embodiments, the sheet-like material pieces are mechanically crinkled, folded, or rolled to introduce random or structured surface geometries.

[0033] In some embodiments, an arrangement of the material pieces creates a macroscopically porous body allowing air and sound to pass into and through the structure.

[0034] In some embodiments, the material pieces are stacked or layered in a regular array, optionally with lateral alignment or rotational patterning to enhance acoustic performance.

[0035] In some embodiments, the thermoplastic material pieces have a thickness in the range of 5 to 200 micrometers. In some embodiments, the arrangement yields a material density of 5 to 50 folded or rolled layers per millimeter along a direction perpendicular to the planar extent of the material pieces.

[0036] In some embodiments, the lateral edges of the material pieces include serrations or undulating geometries to increase surface area and create a gradient of porosity.

[0037] In some embodiments, the serrated edges of the material pieces are oriented toward the sound incident surface of the structure.

[0038] In some embodiments, a housing having one or more openings to allow incident sound to enter the porous body formed by the material pieces.

[0039] In some embodiments, the material pieces are oriented such that their serrated edges face the sound entrance opening of the housing.

[0040] In some embodiments, the material pieces comprise entangled or randomly arranged plastic tapes forming a disordered porous structure. In some embodiments, the tapes have non-uniform widths and thicknesses to introduce acoustic scattering and variation in sound paths.

[0041] In an aspect, the present invention relates to the use of the sound-absorbing structure of any one of the preceding claims in an acoustic panel, sound absorption unit, or interior sound treatment installation.

[0042] In one aspect, a sound absorber is disclosed which comprises at least one and preferably a plurality of material pieces, such as sheets, tapes, or membranes, for sound absorption, wherein each material piece consists of or at least comprises an elastic material.

[0043] The sound absorber described herein may thus use a new category of sound-absorbing material that differs fundamentally from the conventional approaches. The material may be based on thin, elastic material pieces, such as sheets, tapes, or membranes, having for example crinkled surfaces that are arranged arbitrarily or for example in parallel layers, thereby offering a novel solution with unique acoustic properties.

[0044] In some embodiments, the material is non-paper like or non-porous-like. In some embodiments, the material is a polymer or a plastic material, such as recycled plastic. In some embodiments, the material is a plastic bag, such as a reused plastic bag.

[0045] In some embodiments, the material is aluminium, such as aluminium foil. This is particular useful for higher temperature applications, for example in a sound absorber for devices and engines.

[0046] In some embodiments, at least one and preferably each of the material pieces is arbitrarily crinkled or arranged in a defined way, in particular folded or rolled.

[0047] In some embodiments, the material pieces of the plurality of material pieces are arranged to form a porous structure. The sound may be absorbed in the porous structure which can result from crinkled surfaces of the material pieces and from air or free spaces between the material pieces of the plurality of material pieces.

[0048] In some embodiments, the layered material pieces of the plurality of material pieces are arranged in a predefined structure. The material pieces can be rolled up or folded. Furthermore, a plurality of rolled material pieces or folder material pieces can be arranged next to each other in a defined way.

[0049] At least in some embodiments, the material of a material piece is a thin material. In some embodiments, each material piece has a thickness in the range from 5 micrometre to 200 micrometre. In some embodiments, a material piece may have a width which is above 5 mm and a length which is above 5 cm.

[0050] In some embodiments, the material pieces are arranged in a layered structure such that a density of layers is in the range from 5 to 50 layers per millimetre as seen in a direction perpendicular to the layers. Therefore, free or air space between layers can help to absorb sound. Moreover, the material pieces can have a crinkled surface, which may also help to absorb sound.

[0051] In some embodiments, at least some of and preferably all the material pieces have a lateral edge and serrations, in particular triangular serrations, are arranged in the lateral edge of the respective material piece. The serrations can further improve sound absorption.

[0052] In some embodiments, one or more material pieces are arranged in a layered structure such that the lateral edges with the serrations are on the same side. The material pieces can be arranged in rolls or folded.

[0053] In some embodiments, one or more material pieces are rolled up to form a roll and wherein a plurality of rolls is arranged such that that the lateral edges with the serrations are on the same side. Sound that enters the rolls on the side of the lateral edges can be absorbed in an improved way.

[0054] In some embodiments, the plurality of material pieces is located in a housing. The housing has at least one sound entrance window, such as at least one opening, for sound to enter the interior of the housing. A housing may serve to protect the plurality of material pieces against external influences.

[0055] In some embodiments, the material pieces that have a lateral edge with serrations are placed in the housing such that the lateral edges face the sound entrance window. Sound which enters through the sound entrance window can thereby be absorbed in the lateral edges.

[0056] The invention also relates to the use of a sound absorber as described herein in or on a sound absorption equipment or in a soundproof room or in an environment where higher temperature occur, such as in or around an engine or another device. A sound absorber in accordance with the present disclosure may be arranged at least partly around an engine or a device.

[0057] At least in some embodiments, the sound absorber comprises a sound-absorbing material composed of multiple thin, elastic, crinkled surfaces. These surfaces, when arranged in parallel layers, may form a porous structure that efficiently dissipates acoustic energy. The material can be fabricated by folding or rolling thin flexible material pieces, such as sheets or films, into layered structures.

[0058] At least in some embodiments, the arrangement of the material pieces, such as sheets, creates a porous structure in which sound absorption occurs through the interaction of sound waves with the irregularly shaped pores formed between the crinkled layers of the material pieces. This interaction may be enhanced by the free flow of air between the layers, allowing for effective sound absorption across a broad frequency range. The material's sound absorption efficiency can be further improved by incorporating serrated edges on the layers, which creates a gradient in the material's density. This gradient reduces sound reflection at the surface, resulting in higher overall absorption.

[0059] At least in some aspects, the disclosure represents a departure from the traditional porous materials used for sound absorption, such as foams, fibers, and granules. While these materials have been widely used and studied, the proposed sound absorber is based at least in some embodiments on thin, crinkled surfaces, which introduce a new mechanism for sound absorption that has not been previously documented in the scientific or technical literature.

[0060] At least in some embodiments, the thin, elastic, crinkled surfaces function as a membrane-like structure that vibrates in response to incident sound waves. This vibration, combined with the viscous losses that occur as sound waves pass through the pores formed between the layers, results in the dissipation of sound energy. Unlike membrane absorbers that function as resonators, the proposed material operates primarily through energy dissipation rather than resonance.

[0061] In some embodiments, a fabrication process for a material of the sound absorber can utilize existing manufacturing techniques. In some embodiments, the material is created by folding or rolling thin, flexible material pieces, such as sheets, into layered structures. These material pieces can be made from various materials, including polymers, recycled plastics, and other flexible substances. The process can be adjusted to produce materials with varying thicknesses and layer densities, depending on the specific application requirements.

[0062] In some embodiments, an additional enhancement for sound absorption involves the use of serrated edges on the material pieces, which introduces a gradient in the material's density. This gradient is crucial for reducing surface reflections and for increasing the absorption coefficient, particularly at higher frequencies. The serrated edges may create zones of varying density, allowing sound waves to penetrate deeper into the material before being absorbed, thereby improving the overall effectiveness of the material.

[0063] In some embodiments, the material pieces are or comprise arbitrarily entangled tapes, in particular made from soft plastic, such as PVC or similar recycled plastic materials. The entanglement of the tapes may enhance sound absorption by increasing the complexity of the porous structure, allowing for improved dissipation of sound energy across a broad frequency range. The tapes may have the form of stripes. A tape may thus be an elongated and ribbon-shaped piece.

[0064] In some embodiments, the material pieces are or comprise arbitrarily entangled tapes, in particular made from soft plastic, such as PVC or similar recycled plastic materials.

[0065] In some embodiments, the tapes have varying widths and thicknesses to further increase sound absorption efficiency by introducing additional irregularities in the structure.

[0066] In some embodiments, the material of at least some of the material pieces, such as sheets, tapes, or membranes, comprises or consists of aluminium, in particular aluminium foil. The aluminium may be capable of withstanding high-temperature environments. In the sound absorber in accordance with at least some embodiments, the aluminium may serve as both a heat-resistant and sound-absorbing layer. The sound absorber may in particular be used for applications in engines, industrial machinery, or other high-temperature settings.

[0067] In some embodiments, the aluminium is combined with other materials such as crinkled or entangled plastic layers, in particular to optimize both heat resistance and sound absorption across a wide range of frequencies.

[0068] In some embodiments, the versatility of the disclosed sound absorber and the used sound-absorbing material makes it suitable for a wide range of applications across different industries. Some of the potential applications include: 1. Acoustic Panels for Music Listening Rooms: The sound absorber can be used to fabricate panels that enhance the acoustic quality of spaces designed for music listening. By reducing unwanted reflections and reverberations, these panels ensure clearer, more accurate sound reproduction. 2. Acoustic Panels for Speech Clarity: In environments where speech intelligibility is critical, such as conference rooms, lecture halls, and theatres, the sound absorber can be used to reduce noise and improve the clarity of spoken words. 3. Noise Reduction in Machinery and Devices: The sound absorber can be integrated into machinery and devices to reduce operational noise, thereby improving the working environment and reducing noise pollution. 4. Recycling of Waste Plastics: The sound absorber can be manufactured using recycled waste materials, such as plastic bags, contributing to environmental sustainability while providing high-performance acoustic solutions. 5. Noise Barriers for Highways: The sound absorber can be used in the construction of noise barriers along highways, helping to reduce traffic noise in adjacent residential areas. 6. Cabin Noise Reduction in Aircraft, Ships, and Vehicles: The sound absorber can be used to reduce cabin noise in various modes of transportation, improving passenger comfort during travel. 7. Aesthetic Enhancements in Spaces: Beyond its acoustic properties, the sound absorber material's unique structure and appearance can be used to create aesthetically pleasing surfaces that enhance the visual appeal of interior spaces. 8. Urban Noise Reduction Facades: The sound absorber material can be integrated into building facades to reduce noise in urban environments, contributing to quieter, more comfortable living conditions.

[0069] The effectiveness of the proposed sound absorber material has been demonstrated through experimental measurements. Samples of the material, fabricated from thin plastic films, were tested in an impedance tube according to ISO 10534-2 standards. The results show that the absorption coefficients of these samples are competitive with, and in some cases superior to, those of commercially available acoustic foams.

[0070] In some embodiments, samples of sound absorbers having material pieces, such as sheets, with serrated edges exhibited higher absorption coefficients at frequencies above 1000 Hz, indicating that the material is particularly effective in absorbing higher-frequency sounds. The serrated-edge design reduces surface reflections and allows sound waves to penetrate deeper into the material, where they are dissipated through the interaction with the crinkled surfaces.

[0071] The theoretical foundation for the sound absorption mechanism in the sound absorber's material differs from the established models used for fibrous materials, open-cell foams, and granular materials. The material may operate on a novel principle of acoustic energy dissipation through the interaction of sound waves with the multi-layered, crinkled structure. To the best knowledge and experience of the inventors, such an approach has not been previously explored in the scientific literature, marking a significant advancement in the field of acoustic materials. At least in some embodiments, the disclosed sound absorber is not only innovative in its design and function, but also in its potential to utilize recycled materials, providing a sustainable and environmentally friendly solution to noise pollution. The ability to manufacture high-performance acoustic materials from waste products may represent a significant step forward in the development of green technologies.

[0072] At least in some embodiments, the disclosed sound absorber may presents a ground-breaking approach to sound absorption by utilizing thin, elastic, crinkled surfaces arranged in parallel layers. The material may offer a superior acoustic performance, particularly in the higher frequency range, and it may be produced using recycled materials, making it both effective and sustainable. A broad range of applications, from architectural acoustics to industrial noise control, highlights its versatility and potential impact on various industries. As an innovative solution to noise reduction, this material addresses the growing demand for effective, sustainable, and aesthetically pleasing acoustic materials. In some embodiments, the described absorber may represent a significant advancement in the field of noise control and may have the potential to set new standards in acoustic material design and application.

[0073] A feature mentioned with regard to one embodiment or aspect may optionally be present in another embodiment or aspect, even if this is not described explicitly.

[0074] Exemplary embodiments of the present invention will be described in the following with reference to the accompanying drawings, in which: Fig. 1a and Fig.1b show rolled sound absorbing structures with (Fig. 1b) and without serrations (Fig. 1a). Fig. 2a and Fig. 2b show sound absorption panels with rolled (Fig. 2a) and folded structures (Fig. 2b). Fig. 3 shows curves of a measured sound absorption coefficient in relation to frequency for non-serrated and serrated rolled samples. Fig. 4a shows a sound absorber with a plurality of tapes as sound absorbing material. Fig. 4b and Fig. 4c show an exemplary tape of the plurality of tapes of the sound absorber of Fig. 4a. Fig. 5 shows a view of an exemplary crinkled and wrinkled material sheet. Fig. 6 shows an example of a folded sheet material piece for a sound absorbing structure. Fig. 7 shows an example of a rolled sheet material piece for a sound absorbing structure. Fig. 8 shows a sound absorbing structure having a plurality of sheet material pieces as shown in Fig. 7.

[0075] The sound absorbing structures as shown in Figs. 1a and 1b include at least one material pieces 11, 13 of sound absorption material. Each material piece 11, 13 has the form of a sheet in the shown examples of Figs. 1 to 3. The sheet 11, 13 consists of or at least comprises a thin and elastic material. In at least some embodiments of the invention, a sound absorber comprises at least one and preferably a plurality of corresponding sheets 11, 13 for sound absorption.

[0076] The material of the sheet 11, 13 may be a non-paper like material. In some embodiments, the material of the sheet 11, 13 is a polymer or a plastic material, such as recycled plastic. In some embodiments, the material is the material of plastic bags. In some embodiments, reused or recycled plastic bags can be used as material for the sheet 11, 13.

[0077] In some embodiments, the sheet 11, 13 has a thickness in the range from 5 micrometre to 200 micrometre. As shown in Figs. 1a and b, the sheet 11, 13 is arranged in a defined way. In particular, the sheet 11, 13 is rolled such as to form a cylindrical structure.

[0078] As can be seen from Fig. 1a, the sheet 11 has, when rolled out, the form of a rectangle. As shown in Fig. 1b, the sheet 13 has a lateral edge 15 with serrations 17. In the shown examples, the serrations have a triangular form.

[0079] As shown in Fig. 2a, rolled up sheets 11, 13 of Fig. 1a or of Fig. 1b can be arranged in a predefined, exemplary structure to form a sound absorption panel 19 of a sound absorber.

[0080] As shown in Fig. 2b, the sheets 11 as shown in Fig. 1a or the sheets 13 as shown in Fig. 1b may be arranged in form of a layered structure 23 to provide a sound absorption panel 21 of a sound absorber. The layered structure 23 may be obtained from an arrangement of folded or stacked sheets of material pieces. Each folded material piece may comprise superimposed parts due to the folding and / or parts of different sheet material pieces may be arranged one above the other due to the folding or stacking. At least some of the superimposed parts and at least some of the parts of different material pieces do not lie directly adjacent to each other, but have small gaps between them for the entrance of sound from the surrounding. The gaps may be due to the folding or stacking being carried out only with a low force and / or due to each material piece or some material pieces having a crinkled or wrinkled texture. In some embodiments, a sequence of sheets 11 of Fig. 1a or of sheets 13 of Fig. 1b may be arranged to form the layered structure 23 instead of being rolled. In the layered structure 23, an individual sheet 11, 13 may be arranged in an unfolded way or each individual sheet 11, 13 may be folded to provide two or more layers of the structure 23.

[0081] A sheet 11, 13 as shown in Figs. 1a or 1b or a panel 19, 21 as shown in Figs 2a or 2b may be used to absorb sound. Preferably, the sheet 11, 13 or panel 19, 21 is arranged such that the sound is incident in a sound direction SD, which is at least approximately parallel to a sheet plane as shown in Figs. 1 and 2. In some embodiments, the one or more sheets 11, 13 are folded such that they have a crinkled surface and / or that there is some air or free space between overlying planes. Therefore, the one or more overlying sheets 11, 13 can be rolled such that a porous structure is formed. For example, the sheets 11, 13 may have a thickness in the range from 5 micrometre to 200 micrometre, and a density of overlying layers may be in the range from 5 to 50 layers per millimetre when seen in a direction perpendicular to the layers. In such structures, noise can in particular be absorbed in the air or free space between the sheets 11, 13.

[0082] In particular, each sheet or at least some of the sheets may have a crinkled or wrinkled structure and / or the sheets may have been rolled with a low force. Thereby, gaps are formed between the rolled sheets 11, 13, either between superposed or overlapping portions of the same sheet or between different sheets. The gaps provide free space in which sound can be absorbed.

[0083] In view of the embodiment of Fig. 1b, the sheet 13 or a corresponding panel 19 is preferably arranged such that the sound is incident on the side of the edge 15 with the serrations 17. An improved sound absorption can therefore be achieved.

[0084] The diagram of Fig. 3 shows along the x-axis the frequency of sound waves in Hertz and along the y-axis an absorption coefficient in relative units between 0 and 1. The curve 31 shows a measured sound absorption for a rolled sheet 13 as shown on the left side of Fig. 3 and in Fig. 1b. The curve 33 shows a measured sound absorption for a rolled sheet 11 as shown on the left side of Fig. 3 and in Fig. 1a. As shown in the diagram of Fig. 3, the sheet 13 in particular provides an improved sound absorption above around 1200 Hertz, whereas the sheet 11 provides a slightly better sound absorption for frequencies below around 1200 Hertz. The principal direction of the incident sound in the measurements was along the sound direction SD.

[0085] In some embodiments, which are not illustrated by a drawing, a sound absorber may comprise a housing in which the plurality of sheets 11, 13 as shown in Fig. 2a, b or a rolled sheet 11, 13 as shown in Fig. 1a, b or a folded sheet is arranged. The housing may have at least one sound entrance window, such as at least one opening, for sound to enter the interior of the housing. Sheets 13 that have a lateral edge 15 with serrations 17 as shown in Fig. 1b may be arranged in the housing such that the lateral edges 15 face the sound entrance window.

[0086] In some embodiments, which are not illustrated by a drawing, the sound absorber may comprise one and preferably a plurality of sheets of a thin and elastic material that are arbitrarily crinkled, for example into a ball-like form. The plurality of sheets may be arranged in a housing with at least one sound entrance window.

[0087] While the Figs. 1 to 3 show sheets 11, 13 as material pieces, the material pieces may also be tapes or membranes.

[0088] Fig. 4a shows a sound absorber with a plurality of tapes 41 as sound absorbing material and which is not covered by the claimed sound absorbing structure. The plurality of tapes 41 is arranged in any configuration in a volume of the sound absorber, in particular to form a porous structure. Fig. 4b and Fig. 4c show an exemplary tape 43, 45 of the plurality of tapes 41 of the sound absorber of Fig. 4a. The tapes 43, 45 have a strip-like form and they can be entangled or otherwise arbitrarily arranged. The entanglement of the tapes 43, 45 in the plurality of the tapes 41 may enhance sound absorption by increasing the complexity of a porous structure, allowing for improved dissipation of sound energy across a broad frequency range.

[0089] The tapes 43, 45 may be made from soft plastic, such as PVC or similar recycled plastic materials. The material of the tapes 43, 45 may have varying widths and thicknesses to further increase sound absorption efficiency by introducing additional irregularities in the structure.

[0090] The material of the tapes 43, 45 may also be a metal, such as aluminium or aluminium foil. Also another metal, such as copper, may be provided in form of a foil. The material may therefore be capable of withstanding high-temperature environments. In the sound absorber, the metal, such as aluminium foil, may serve as both, a heat-resistant and sound-absorbing layer, in particular for applications in engines, industrial machinery, or other high-temperature settings.

[0091] The metal, such as aluminium foil, may be combined with other materials such as crinkled or entangled plastic layers to optimize both heat resistance and sound absorption across a wide range of frequencies.

[0092] Fig. 5 shows a view of an exemplary crinkled and wrinkled material sheet. Such a material sheet can be made from a standard non-crinkled or non-wrinkled material sheet, for example a thermoplastic or paper sheet or a metal sheet, such as aluminium, which is crumpled up. When it is laid out again as a sheet, it has a wrinkled or crinkled texture. Such a wrinkled or crinkled texture may also provide stability to the sheet.

[0093] Fig. 6 shows an example of a folded sheet material piece 601 for a sound absorbing structure or apparatus, which can be made of a plurality of such sheet material pieces, in particular arranged in a particular structure. The sheet material piece can consist of a thermoplastic material.

[0094] As shown in Fig. 6, the sheet material piece 601 is folded such that the piece comprises superimposed parts which are arranged one above the other. The superimposed parts do not lie directly adjacent to each other, but have small gaps 603 between them, thereby providing free space for the entrance of sound from the surrounding. The material piece 601 may be further crinkled or wrinkled to improve the absorption of sound in the gaps 603.

[0095] A plurality of such sheet material pieces 601 may be arranged in a defined structure in a sound absorber. At least some and preferably all of the sheet material pieces 601 may have serrations (not shown in Fig. 6), such as triangular serrations as shown in Fig. 1b, at least on one edge of the sheet material piece 601, for example on the edge that is on the top side in the view of Fig. 6.

[0096] Preferably, the sheet material pieces 601 of a plurality of pieces are arranged in a defined structure such that the edges with serrations of the sheet material pieces lie on one side of the structure, for example the serrated edges of all sheet material pieces may face upwards with regard to the view of Fig. 6. In the intended use of the sound absorbing structure, the upward facing side of the structure would then be arranged such that a main direction of incoming sound hits at this side the sheet material pieces 601.

[0097] As shown in Fig. 6, the gaps 603 are open to the upper side of the structure, so that sound can enter the gaps 603 and get absorbed or at least reduced.

[0098] As further shown in Fig. 6, the folded sheet material piece 601 has a central axis CA extending along a folding edge of the sheet material piece 601. In some embodiments, a plurality of sheet material pieces 601 is arranged in a defined structure, where the main structure defines a main axis, for example a vertical axis in Fig. 6, and the folded sheet material pieces 601 are arranged such that the central axis CA of each sheet material piece 601 is at least approximately parallel to the main axis (vertical axis in Fig. 6). In some embodiments, the central axes CA of at least some sheet material pieces 601 are inclined to the main axis, at a maximum angle of no more than 60 degrees, preferably no more than 30 degrees, and more preferably no more than 15 degrees. Arranging the folded sheet material pieces at an angle with regard to a main axis, such as a vertical direction in Fig. 6, where the main axis may correspond to the main direction of incoming sound, can be advantageous for sound absorption at some frequencies, in particular higher frequencies.

[0099] Fig. 7 shows an example of a rolled sheet material piece 701 for a sound absorbing structure, and Fig. 8 shows a sound absorbing structure having a plurality of rolled sheet material pieces 701 of Fig. 7.

[0100] The rolled sheet material piece 701 of Fig. 7 has a crinkled or wrinkled structure and has triangular serrations 703 on an edge and further comprises superimposed parts due to the rolling of the piece 701 around a central axis CA. The superimposed parts may not lie directly adjacent to each other, but have small gaps 705 between them for the entrance of sound from the surrounding. The embodiment of Fig. 7 is similar to the one of Fig. 1b, but Fig. 7 illustrates the presence of gaps 705 in an improved way.

[0101] As shown in Fig. 8, sheet material pieces 701 of Fig. 7 are arranged in a defined structure such that the edges with serrations of the sheet material pieces lie on the upper side. During the intended use of the sound absorbing structure, the upper side of the structure is preferably arranged such that a main direction of incoming sound, see sound direction SD in Fig. 7, hits at this side the structure. The embodiment of Fig. 8 may be similar to the embodiment of Fig. 2a.

[0102] As further shown in Fig. 8, the defined structure, in which the rolled pieces 701 are arranged, defines a main axis or main direction MD. The rolled sheet material pieces 701 are arranged such that their central axes CA are at least approximately parallel to the main direction MD. The central axes CA of at least some of the sheet material pieces 701 may be inclined to the main direction MD, for example at a maximum angle of no more than 60 degrees, preferably no more than 30 degrees, and more preferably no more than 15 degrees.

[0103] Stacked or folded sheet material pieces may also be arranged in a structure as shown in Fig. 8, where a central plane of stacked pieces, which extends in parallel to the sheet plane of the sheet material pieces, or a central axis CA of folded pieces is arranged in parallel or at an angle with regard to a main direction MD of the structure.

[0104] Further Embodiments and examples in accordance with the present invention are also described in the following list of items: 1. A sound absorber comprising at least one and preferably a plurality of material pieces (11, 13), such as sheets, tapes, or membranes, for sound absorption, wherein each material piece (11, 13) consists of or comprises an elastic material. 2. The sound absorber of item 1, wherein the material of the material piece (11, 13) is non-paper and / or nonporous like, and / or wherein the material is a polymer or a plastic material, such as recycled plastic, or wherein the material is a plastic bag, such as a reused plastic bag, or wherein the material is a metal, such as aluminium, in particular a metal foil, such as an aluminium or copper foil. 3. The sound absorber of item 1 or 2, wherein at least some and preferably each of the material pieces, such as sheets, is arbitrarily crinkled and / or arranged in a defined way, in particular folded or rolled. 4. The sound absorber of any one of the preceding items, wherein the material pieces, such as sheets (11, 13), of the plurality of sheets is arranged to form a porous structure. 5. The sound absorber of any one of the preceding items, wherein the material pieces (11, 13) of the plurality of material pieces are arranged in a predefined structure. 6. The sound absorber of any one of the preceding items, wherein each material piece (11, 13) has a thickness in the range from 5 micrometre to 200 micrometre. 7. The sound absorber of any one of the preceding items, wherein the material pieces (11, 13) are arranged in a layered structure such that a density of layers is in the range from 5 to 50 layers per millimetre as seen in a direction perpendicular to the layers. 8. The sound absorber of any one of the preceding items, wherein at least some and preferably all of the material pieces have a lateral edge, wherein serrations, in particular triangular serrations, are arranged in the lateral edge of the respective sheet (11, 13). 9. The sound absorber of any one of items 7 to 8, wherein the material pieces (11, 13) are arranged in a layered structure such that the lateral edges with the serrations are on the same side. 10. The sound absorber of any one of items 7 to 9, wherein one or more material pieces (11, 13) are rolled up to form a roll and wherein a plurality of rolls is arranged such that that the lateral edges with the serrations are on the same side. 11. The sound absorber of any one of the preceding items, further comprising a housing in which the plurality of material pieces (11, 13) is arranged, wherein the housing has at least one sound entrance window, such as at least one opening, for sound to enter the interior of the housing. 12. The sound absorber of item 11, wherein material pieces (11, 13) that have a lateral edge with serrations are arranged in the housing such that the lateral edges face the sound entrance window. 13. The sound absorber as in any of the preceding items, wherein the material pieces are or comprise arbitrarily entangled tapes (41, 43, 45), in particular made from soft plastic, such as PVC or similar recycled plastic materials. 14. The sound absorber of item 13, wherein the tapes have varying widths and thicknesses to further increase sound absorption efficiency by introducing additional irregularities in the structure. 15. The sound absorber as in any of the preceding items, wherein the material of at least some of the material pieces, such as sheets, tapes, or membranes, comprises or consists of a metal, such as aluminium, in particular aluminium foil, capable of withstanding high-temperature environments, wherein, in the sound absorber, the metal, such as aluminium, serves as both a heat-resistant and sound-absorbing layer, in particular for applications in engines, industrial machinery, or other high-temperature settings. 16. The sound absorber of item 15, wherein the metal, in particular aluminium, is combined with other materials such as crinkled or entangled plastic layers to optimize both heat resistance and sound absorption across a wide range of frequencies. 17. Use of a sound absorber as in any one of the preceding items in a sound absorption equipment or in a soundproof room or in an environment where higher temperatures occur, such as in the vicinity of or around an engine. List of reference signs

[0105] 11sheet 13sheet 15edge 17serration 19sound absorption panel 21sound absorption panel 23layered structure 31sound absorption curve 33sound absorption curve 41plurality of tapes 43tape 45tape 601sheet material piece 603gap 701sheet material 703serration 705gap CAcentral axis MAmain axis SDsound direction

Claims

1. A sound-absorbing structure, comprising: a plurality of sheet material pieces, optionally made of thermoplastic sheet material or optionally made of a metal sheet material, such as aluminium, wherein the sheet material pieces are stacked, rolled or folded such that each piece comprises superimposed parts and / or parts of different sheet material pieces are arranged one above the other, wherein at least some of the superimposed parts and at least some of the parts of different material pieces do not lie directly adjacent to each other, but have small gaps between them for the entrance of sound from the surrounding, and wherein at least some and preferably all sheet material pieces have a crinkled or wrinkled structure.

2. The sound-absorbing structure of claim 1, wherein the plurality of the sheet material pieces is arranged in a defined structure.

3. The sound absorbing structure of any one of the preceding claims, wherein at least some and preferably all of the sheet material pieces have serrations, in particular triangular serrations, at least on one edge.

4. The sound absorbing structure of claim 3, wherein the sheet material pieces are arranged in a defined structure such that the edges with serrations of the sheet material pieces lie on one side of the structure, wherein, preferably, for the intended use of the sound absorbing structure, the side of the structure being arranged such that a main direction of incoming sound hits at this side the structure.

5. The sound absorbing structure of any one of the preceding claims, wherein at least some of the gaps between material pieces are open to one side of the structure, in particular such that sound can enter the gaps on this side.

6. The sound absorbing structure of any one of the preceding claims, wherein a rolled sheet material piece has a central axis around which the material piece is rolled and / or wherein a folded material piece has a central axis extending along a folding edge of the sheet material piece.

7. The sound absorbing structure of claim 6, wherein the plurality of sheet material pieces is arranged in a defined structure, which defines a main axis, and wherein the rolled or folded sheet material pieces are arranged such that the central axes of the sheet material pieces are at least approximately parallel to the main axis or the central axes of the sheet material pieces are inclined to the main axis, at a maximum angle of no more than 60 degrees, preferably no more than 30 degrees, and more preferably no more than 15 degrees.

8. The sound absorbing structure of any one of the preceding claims, wherein stacked sheet material pieces have a central plane which extends in parallel to the sheet plane of the sheet material pieces.

9. The sound absorbing structure of any one of the preceding claims, wherein the plurality of sheet material pieces is arranged in a defined structure, which defines a main plane, and wherein the stacked material pieces are arranged such that the central planes of the sheet material pieces extend at least approximately parallel to the main plane or the central planes of the sheet material pieces are inclined to the main plane, at a maximum angle of no more than 60 degrees, preferably no more than 30 degrees, and more preferably no more than 15 degrees.

10. The sound absorbing structure of any one of the claims 7 to 9, wherein, in particular for the intended use of the sound absorbing structure, the sheet material pieces are arranged such that their main axes and / or their main planes are arranged at least approximately in parallel to a main direction of incoming sound.

11. The sound absorbing structure of any one of the preceding claims, wherein the gaps have a non-uniform width.

12. A sound absorbing structure, in particular in accordance with any one of the preceding claims, comprising at least one and preferably a plurality of material pieces (11, 13), such as sheets, tapes, or membranes, for sound absorption, wherein each material piece (11, 13) consists of or comprises an elastic material, wherein at least some and preferably all of the material pieces have a lateral edge, wherein serrations, in particular triangular serrations, are arranged in the lateral edge of the respective sheet (11, 13), wherein one or more material pieces (11, 13) are rolled up to form a roll and wherein a plurality of rolls is arranged such that that the lateral edges with the serrations are on the same side.

13. Use of the sound-absorbing structure of any one of the preceding claims in an acoustic panel, sound absorption unit, or interior sound treatment installation.

14. A sound absorber comprising a housing having an entrance for sound at least on one side and a sound absorbing structure as defined in any one of the claims 1 to 12, wherein the sheet material pieces are arranged in a defined structure such that a side of the structure, which is intended for sound absorption, is oriented towards the entrance of the housing.

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