Sound reduction devices, system comprising such a sound reduction device, use of a porous absorber for sound reduction, use of such a sound reduction device, and method of manufacturing such a sound reduction device

Abstract

Sound reduction device, comprising a porous sound absorber and a skin, wherein the porous sound absorber has a density of 0.3 g / cm3 or less, wherein the skin is arranged on a surface of the porous sound absorber, and wherein the skin shields at least a portion of the surface of the porous sound absorber from the environment. Preferably, the skin shields the entire surface of the porous absorber from the environment.

Description

[0001] SOUND REDUCTION DEVICES, SYSTEM COMPRISING SUCH A SOUND REDUCTION DEVICE, USE OF A POROUS ABSORBER FOR SOUND REDUCTION, USE OF SUCH A SOUND REDUCTION DEVICE, AND METHOD OF MANUFACTURING SUCH A SOUND REDUCTION DEVICE

[0002] The present invention relates to sound reduction devices, a system comprising such a sound reduction device, a use of a porous absorber for sound reduction, a use of such a sound reduction device, and a method of manufacturing such a sound reduction device.

[0003] The absorption of mid to high frequencies can typically be achieved by applying readily available porous broadband absorbers, frequently in form of wall or ceiling panels, baffles, or high-volume objects which sometimes provide for voluminous geometric surface structures in manifold designs. Such devices are featured from or contain the porous absorber. Such porous absorbers are usually made from plastics (for example polyesters), foams, resins, mineral wool, fiberglass, or anything the like or combinations thereof. Due to their principle mode of action, the surface of such porous absorbers is exposed and open to the environment.

[0004] Mid and in particular low frequency broad band absorption in general and in particular when the absorbing system is supposed to be shielded for use in highly qualified surroundings such as clean rooms, still remains a challenge.

[0005] Resonant absorbers that is typical membrane and / or panel absorbers as well as Helmholtz resonators, respectively, are individually designed and used to control very low and highly specified frequencies, typically lower than 80 Hz, accordingly in very specific and stationary settings. However, similar as porous absorbers, the great majority of resonant absorbers is not constructed and / or assembled in a sealed manner and thus equally detrimental, if not inapplicable, as to highly qualified clean room requirements.

[0006] Because conventional porous absorbers by principle do not resonate and thus do not require any particulate attention or need to be specifically adjusted to their particulate environments and the impeding frequencies to be absorbed, such systems may be considered generally and easily applicable, however, provided that no sealing requirements along with respective hygiene requirements are stipulated.

[0007] Conventionally, only upon significant increase of the porous absorber's respective surface density and / or overall mass, e. g. by increasing the panels thickness or traversed area, a frequency shift towards the absorption of mid to lower frequencies may be observed at a given pore and object geometry because the thickness of the material needed for it to be effective increases with the wavelengths getting longer.

[0008] However, efficacy will cease when approaching a certain threshold and renders such approach obviously unviable from commercial and in particular practical considerations. Obviously, such measures are markedly ineffective and mass and volume of such panels and / or objects, in particular when low-expansion acoustic foams or highly compressed mineral rock wool or highly compressed fiberglass or any combination thereof is used, are considered a limiting factor in terms of available space and static considerations concerning the load-bearing structures for fixing them in the respective environment.

[0009] While being a stationary solution, the mentioned materials used for porous absorbers may additionally pose severe health and environmental hazards, especially if not shielded from the environment, and are thus problematic to handle and particularly to discard. Further, as indicted above, said materials are considered unapplicable in clean room environments due to the nature of their open surface releasing particles and vaporable residues to the room’s atmosphere which renders them virtually uncleanable under controlled conditions.

[0010] While accordingly coated mineral wool or rockwool panels are commercially available to address this specific hygiene requirements issue, such panels display loss of efficacy, obviously because the coating counteracts the mode of action of porous absorbers by sealing the pores.

[0011] Resonant absorbers, that is typical membrane / panel absorbers as well as Helmholtz resonators, respectively, in contrast, are designed to address very specific frequencies, typically lower than 80 Hz in very specific and stationary settings. In contrast to porous absorbers, such resonant absorbers need to be mechanically adjusted to the specific frequencies required to be absorbed in the individual room and sound setting. Hence, such systems are effective in a very specific, narrow frequency range only, invariant, not displaying any significant broadband absorption and are virtually not fit for use in changing environments or settings.

[0012] Typical membrane / panel absorbers in contrast to porous absorbers consist of a membrane or a flat panel being arranged in front of an enclosed air volume and require an additional stable mounting, such as an external frame, for mounting the membrane or panel, respectively, that acts like a freely moving mass that resonates in accordance with the frequencies to be absorbed.

[0013] Typically, they are realized as rigid containers with a flexible diaphragm. Increasing the freely moving mass thereby continuously shifts the resonant frequency of such system from higher to lower frequencies. The construction may additionally contain an internal acoustic insulation like mineral wool or comparable material to provide for a more balanced frequency spectrum, necessitating and open construction, e.g. by using perforated foils or panels and / or openings to resonance body.

[0014] Other constructions provide for panels being glued over their entire surface area to a foam layer located in front of a rigid wall allowing oscillation on the spring formed by the foam layer. The heavier the panel and the softer the foam layer, the lower its resonance frequency, provided that the panel or membrane may oscillate freely, requiring the panel or membrane not to be constricted by the mounting, otherwise resulting in further limiting efficacy to most specific frequencies and system solutions that need to be very skillfully adjusted.

[0015] Helmholtz resonators, in turn, are designed as voluminous rigid (open) containers with one or more portholes or slots to silence either single or multiple frequencies, with round port, slotted port, or even perforated constructions. Resonating absorbers often incorporate porous absorption material internally to simultaneously lower the resonant frequency and broaden the spectrum of absorption. The obvious broadband absorption gap between the performance range of porous and resonant absorbers yet cannot generally be closed by applying satisfying standardized solutions, but requires sophisticated calculations, skillful adjustments, a plurality of systems and hence expensive as well as extensive constructive measures to be employed.

[0016] In view of the above, it is an objective of the present invention to provide an improved sound reduction device, in particular an improved sound reduction in the frequency range of approximately 80 to 1500 Hz and / or a with improved shielding from the environment. This object is achieved by the sound reduction device according to claim 1 , the system according to claim 15, the uses according to claims 18 and 20, and the method according to claim 21 . Exemplary embodiments are defined in the dependent claims. The features that are defined for the devices according to the invention in the dependent claims and in the description below may also serve as a basis for further embodiments of the system, the uses, and the method according to the invention.

[0017] In particular, it is a specific object of the present invention to provide a fully self- contained and easy to use broadband sound reduction device displaying high absorption rates between approximately 80 and 1500 Hz and being suitable for highly qualified room settings (such as cleanrooms).

[0018] Specific features and expediencies of the present invention may be found in the description of exemplary embodiments with the aid of the appended drawings.

[0019] Fig. 1 shows frequency dependent absorption data measured for various sound reduction devices according to embodiments of the present invention.

[0020] Fig. 2 shows a schematic cross-sectional view of a sound reduction device according to an embodiment of the invention.

[0021] The sound reduction device according to an embodiment of the present invention is a sound reduction device comprising a porous sound absorber and a skin, wherein the porous sound absorber has a density of 0.3 g / cm3or less, preferably 0.2 g / cm3or less, more preferably 0.1 g / cm3or less, even more preferably 0.05 g / cm3or less, most preferably 0.02 g / cm3or less wherein the skin is arranged on a surface of the porous sound absorber, and wherein the skin shields at least a portion of the surface of the porous sound absorber from the environment.

[0022] In Fig. 2, the cross-section of a sound reduction device 1 according to an embodiment of the present invention is shown. According to this embodiment, the skin 3 is arranged on all outer sides of the porous sound absorber 2, of which four are shown in the cross-sectional view. According to this embodiments, the outer sides are completely shielded by the skin. According to other embodiments, the skin 3 is not present on all outer sides. According to other embodiments, the skin 3 covers only a part of a side surface.

[0023] Preferably, the porous sound absorber has a density of 0.001 g / cm3or more, more preferably 0.005 g / cm3or more, even more preferably 0.007 g / cm3or more.

[0024] Alternatively, the porous sound absorber preferably has a density of 0.01 g / cm3or more.

[0025] Preferably, the skin shields the entire surface of the porous absorber from the environment. This means that the skin covers the entire porous absorber such that the porous absorber has no contact to the environment. If the skin shields the entire surface of the porous absorber from the environment, the sound reduction device may be considered as a "self-contained sound reduction device". More preferably, the skin shields the entire surface of the porous absorber from the environment such that no gas exchange (e.g. air exchange or exchange of nitrogen) is possible between the porous absorber and the environment.

[0026] If the skin shields the entire surface of the porous absorber from the environment, not only the acoustic properties of the sound reduction device may be improved but also, e.g., its suitability for cleanroom applications.

[0027] According to a non-limiting theory, the skin of the sound reduction device according to the invention has the effect of a membrane. However, in contrast to conventional membrane absorbers, the sound reduction properties may improved by the present invention for instance in the sense of a broader absorption spectrum. Therefore, the sound reduction device according to the invention may be considered to as "atypical membrane absorber".

[0028] As mentioned, the sound reduction device according to the invention differs from a conventional membrane absorber with respect to its acoustic properties. Hence, the porous absorber and / or the specific combination of the porous absorber and the skin contribute to the acoustic properties. In this sense, the sound reduction device according to the invention may be considered as an advantageous system comprising a porous absorber and a skin coating the porous absorber.

[0029] Further embodiments of the invention are described below and defined in the claims.

[0030] Overall, porous absorbers tend to be smaller in size and are easier to design and build, as well as less expensive than resonant absorbers (hereinafter also referred to as "resonators"). However, conventional porous absorbers proof ineffective at low frequencies or proof unviable due to space and static requirements in such scenarios. Conventional resonators, in turn, can be very effective over their tuned range, but require a lot of space, especially when installed in arrays, are heavy by principle, invariant and inflexible towards changing room and application settings and thus are commonly not a practical solution in changing and confined environments. For instance, windows, doors, furnishings, pieces of equipment, etc. may be an obstacle to the installation and / or functionality of acoustic systems. In addition, lighting fixtures, air filter outlets, and other appliances arranged on the ceiling or walls may make it inefficient or impossible to install as many porous absorbers and / or resonators as would be required to provide for marked sound reducing effects because dimensions of such systems would interfere with such appliances. In addition, because of filter fan units or air filter outlets usually mounted on the ceiling of for example cleanrooms, sound baffles cannot be installed there. Hence, the use of sound-reducing devices is especially problematic in the case of cleanrooms as high level of containment, cleanliness and cleanability is required. The same applies to other rooms with specific requirements for cleaning or with high levels of chemicals, vapours, etc. These can be, for example, production facilities, laboratories, kitchens etc. Hence, fully sealed surfaces of respective absorbers or resonators are advantageous because they provide for the respective surface properties. Obviously, on the one hand, such intended use renders standard systems such as porous absorbers or Helmholtz resonators inapplicable by principle. However, on the other hand, sealing renders absorption rates of conventional sound reduction devices inferior due to the natures of porous absorption and Helmholtz resonators themselves. For example, coated compressed glass and / or rock wool as realized in selected individual products from the commercially available Ecophon Hygiene™ series, some of which claiming cleanroom suitability, have been brought to market. These panels are available in 20 and up to 40 mm thicknesses (up to 50 mm, if used as baffles), only, each depending on the individual product. However, these panels provide for a high area density of not less than approx. 3 kg / m2(20 mm variants) and up to about 5 kg / m2(40 mm variants), including their supporting structure. Herein, even if the weight of said suspension grid is not considered, this equals up to a volume density of approximately 0.125 to 0.150 g / cm3, presumably limiting their scalability to a thickness of 40 to 50 mm, simply because of inherent net weight. In contrast, porous absorber materials like high expansion foams, for example Basotect®, as commercially provided by BASF company, display a volume density of as low as, for instance, about 0.01 g / cm3, only, obviously providing for significant advantages in terms of overall weight and ease of installation. However, as is, they are - due to the open and unshielded surface, by principle - not applicable in high requirement cleanroom settings. In preferred examples, Basotect® (in particular Basotect® B) is used as porous sound absorber of the Sound reduction device according to the present invention.

[0031] To date, despite low frequency absorption is often considered the most necessary objective to be achieved in general and particularly specific room settings, not much practical technical progress in solving this particulate issue has been reported and no generally applicable shielded and light-weight mid to low frequency broad band absorbing system combining the advantages of versatile porous and effective resonant absorbers is available to the market.

[0032] By the present invention, for instance an easily tunable effective mid to low frequency broad band sound reduction may be provided which is at the same time versatile, generally applicable, and in particular scalable like aforementioned porous absorber panels. By the present invention, for instance a sound reduction may be provided in a manner intrinsically suitable for use in environments where specific necessities as to space restrictions, cleanability and specific surface requirements are to be met, without impacting, but most preferably even improving its mid to in particular low frequency absorption capacity by specifically coating and selecting the core material of the sound reduction device. Hence, a particularly lightweight passive sound reduction device and system, the manufacturing and use thereof, and a sound- reduced room with such sound-reducing system or device or an arrangement of a plurality of such sound-reducing devices, will be outlined herein.

[0033] The following specific features of the sound reduction device according to the invention may be combined with each other resulting in various embodiments of the invention.

[0034] Preferably, the sound reduction device according to this invention is a light-weight sound-reducing device comprising at least two components, that is firstly a porous absorber material, preferably selected from resins and foamed plastic, preferably selected from the group of duroplastics, more preferably an acoustic foam, more preferably a high expansion acoustic foam, especially foamed melamine resin, and secondly a light-weight coating used as the skin, whereas said coating fully shields the porous absorber material from the surrounding environment.

[0035] Preferably, the sound reduction device consists of light-weight panel-like cores that have a surface coating (skin) fully sealing the surfaces of the core from the surrounding environment.

[0036] More preferably, these panels may be provided in different, preferably rectangular dimensions, even more preferably in dimensions of 1200 mm x 600 mm, 625 x 625 mm, or 600 mm x 600 mm, most preferably as a tailor-made solution, complying with any specific demand or given architectural requirements.

[0037] Preferably, the porous absorber material is provided as a panel, preferably in different thicknesses (i.e. heights perpendicular to the main surfaces of the panel), preferably thicknesses of less than 150 mm, more preferably less than 125 mm, even more preferably 120 mm or less, and in particular equaling 120, 110, 100, 80, 60, and 40 mm, respectively.

[0038] Preferably, the sides and edges of said porous absorber panels are chemically and / or physically treated, in particular in order to provide for reinforced adjacent side surfaces and edges. Herein, physical treatment may include application of pressure and / or heat. Chemical treatment may include the application of a chemical, e.g. an organic solvent. The stiffening of the sides and edges may improve the mechanical rigidity of the sound reduction device which may in turn improve the handling of the device and surprisingly also its acoustic properties. Moreover, the stability of the porous absorber under vacuum conditions that may be used when applying the skin (see below) may be enhanced.

[0039] More preferably, said chemically and / or physically reinforced adjacent panel sides and edges provide for a supporting structure for an atypical membrane resonance effect in connection with the preferred high-expansion acoustic foam that is tightly sealed by the low-weight coating (skin), resonating as a whole system, without the need for external frameworks allowing any individual membrane or panel to resonate in a respective cavity in terms of a freely moving oscillating mass.

[0040] In preferred embodiments, the sound reduction device displays a volume density as low as about for example 0.05 g / cm3, more preferably less than 0.025 g / cm3, and most preferably about 0.015 g / cm3or less.

[0041] Preferably, the sound reduction device provides for an area density (also referred to as "area weight") of preferably less that 3 kg / m2, more preferably less that approximately 2 kg / m2, even more preferably less than 1.8 kg / m2and most preferably less than 1 .5 kg / m2. For instance, if the sound reduction device is a panel with the dimensions 1200 mm x 600 mm x 40 mm, i.e. a panel with main surfaces both having an area of 1200 mm x 600 mm = 1 .2 m x 0.6 m = 0.72 m2, and if this panel has a total mass of 1 .5 kg, then an area weight of 2.08 kg / m2results. These values apply if the devices are installed over the entire surface of the wall, the ceiling, etc.

[0042] Preferably, however, it is also possible that the sound reduction devices according to the invention are not installed over the entire surface of the wall, the ceiling, etc. but as individual unconnected panels, which further reduces the material consumption and also enables, for example, effective utilization of the edge effects.

[0043] The sound reduction system according to the invention comprises a sound reduction device according to the invention and a further component, preferably a fastener such as magnetic fixings and / or no-residue nano polymer adhesives are be used for attaching the panels to the wall, ceiling, floor, grid, or any other supporting structure bearing the device, preferably to the ceiling and / or the wall, in order to provide for a closed surface, more preferably, as a fully suspended ceiling covering the whole traversed area in an intrinsic closed surface, even more preferably to provide for an closed suspended openwork structure to recess any constructive obstacles while being particularly effective, and most preferably as individually placed unconnected panels in a manner so that the devise can be reversibly mounted and unmounted, adapted and adjusted to continuously changing requirements, specifically in a very simple and in particular in a residue-free manner.

[0044] Preferably, the magnetic fixings is shielded from the environment by the skin.

[0045] More preferably, the magnetic fixing is incorporated into the core of the device and fully sealed from its surroundings by the respective durably affixed coating (skin) and whereas the magnetic fixing is realized by either incorporating magnets into the melamine resin while magnet should be understood as bar magnets or anything the like, or alternatively where, more preferably, magnet is to be understood as magnet strips or foils attached directly or indirectly to the lower bottom of the respective melamine resin panel, fully covered by the coating (skin) and fully sealing the device from its surroundings as referred to above.

[0046] Preferably, aforesaid sealing of the surfaces of the core from the surrounding environment is virtually gas-tight.

[0047] Preferably, aforesaid sealing of the surfaces of the core from the surrounding environment is neither chemically nor otherwise bound (that is, for example, glued) to the porous absorber materials surface while resting firmly, virtually without any spacing on the absorber material causing the mode of action to be changed from porous to untypical resonance absorption while still providing for marked broadband efficacy, in particular when compared to specially tuned panel and membrane absorbers.

[0048] Preferably, the coating (skin) is virtually emission free, wipeable and / or washable, preferably suitable for wiping and / or washing and / or disinfection and / or sterilisation and / or decontamination applying cleaning agents containing biological and / or chemical detergents and / or organic solvents and / or water, acids or bases, and whereas the coating (skin) is preferably a foil, made from materials preferably selected from the group of synthetic materials, such as plastics, preferably polymers and / or copolymers, such as polyolefins, more preferably from the groups of thermoplastics (e.g. halopolymers) and elastomers, most preferably PE, PVC, PVF, PTFE, PDVC, PDVF, and / or anything the like.

[0049] Preferably, the skin is provided as a foil, more preferably a foil having a thickness of less than 1 mm, even more preferably 0.5 mm, most preferably less than 0.3 mm, and specifically less than 0.2 mm. For example, the foil may be a LD-PE (low-density polyethylene) foil having a thickness of 0.1 mm ± 10% (i.e. 100 pm ± 10 pm).

[0050] Preferably, for manufacturing the sound reduction device, the porous absorber material is incorporated into the coating under vacuum, while the coating is sealed. Herein, more preferably, the porous absorber material is devoid of any type of mineral rock wool, fiberglass, etc. Herein, most preferably, the sound reduction device is devoid of anything apart from the porous absorber, the coating, and an optional fastener.

[0051] Preferably, the sound reduction device displays an effective range from about 80 Hz to approximately 1250 Hz (that is in the following referred to the effective resonance absorption range while frequencies higher than about 1250 Hz are disregarded because of reflection effects caused by the cut off of the respective coating material used as the skin). The preferred absorption frequencies, however, range between approx. 80 Hz and approx. 1000 Hz, more preferably in the range from about 80 Hz to about 630 Hz, even more preferably in the range from about 80 to about 400 Hz, most preferably between approx. 80 Hz and 150 Hz as exemplified in the following specific examples.

[0052] Specific examples of the sound reduction device according to the invention were produced by covering the entire surface of porous absorber panels with a polymeric skin. As porous absorber panels, panels made from an open-cell melamine resin foam commercialised by BASF SE under the tradename Basotect® were used. The panels had a size of 1200 mm x 600 mm or 600 mm x 600 mm. The panels had a thickness of 120 mm, 80 mm, and 40 mm. For the skin a LD-PE foil having a thickness of 100 pm ± 10 pm was used. The foil was arranged around the porous absorber and sealed under reduced pressure such that the porous absorber became enclosed within the skin in tight-manner.

[0053] For the specific examples and comparative examples, absorption data were measured using the method according to the industrial standard DIN EN 354:2003. For the measurements, rectangular arrays of the panels according to the specific examples having a specific thickness (coated panels, i.e. panels with skin, hereinafter also designated by "c") and rectangular arrays of the comparative examples having a specific thickness (uncoated panels, i.e. panels without skin, hereinafter also designated by "u") were placed on the floor. The rectangular arrays had a total size of 5.4 m x 2.4 m and consisted of four rows of panels, wherein the first row consisted of nine 600 mm x 600 mm and the second to fourth rows consisted of four 1200 mm x 600 mm and one 600 mm x 600 mm panel. Other than according to the method of the mentioned standard, the edges of the panels were not protected by a frame in order to suppress acoustic side and edge effects. This was not done in the present case because the focus is on the comparison of the panels with skin and without skin for which the same edge effects are to be expected such that the edge effects do not affect the comparison. These measurements were performed independently for each of the selected panel thicknesses (120 mm, 80 mm, and 40 mm). The measured data are shown in Fig. 1 . Herein, the measurements are represented by square and triangle symbols. For clarity, the measuring points are connected with straight lines that serve as a guide for the eye. Absorption data connected with solid lines are data obtained with sound reduction devices according to the invention and data connected with dashed lines are observed with the measurements with respectively uncoated specimen of equal thicknesses for direct comparison. Observed absorption rates exceeding a frequency dependent absorption coefficient of 1 are due to unspecific edge and side effects as indicated in Fig. 1 . These edge and side effects are equal when comparing coated and uncoated panels that are analogous otherwise. That is, these edge and side effects occur at least in comparable magnitudes during the measurements, applying identical conditions, so that in the following reference is made to absorption coefficients of 100, 80, and 50 % that is as100, as80and as50and asmaxfor further comparison. The absorption coefficient that is symbolised by the letter "a" above, may also symbolised by the Greek letter "a" below. The meaning of "a" and "a" is the same.

[0054] It is noted that the conversion of alpha values from thirds to octaves is for example described in the standard DIN EN ISO 354:2003. The conversion is also described for example in ISO 11654 (section 8.3). Single-number values can be calculated as follows for example according to ISO 11654: Octave band values are determined by calculating the arithmetic mean value of three sound absorption coefficients for thirds within the octave.

[0055] Preferably and as illustrated in Fig. 1 , the sound reduction device shows a significant shift of asmax, as100, as80and as50from higher to lower frequencies when compared to its respective uncoated analogues, whereas as100, as80and as50shall be construed as the ultimate drop of the frequency dependent absorption curve below the reference values of as= 100, 80 and 50 %, respectively within the specified range of about 80 to 1000 Hz as mentioned. asmaxrefers to the individual maximum absorption, including edge and side effects associated with the measurement. Breakeven that is in the following referred to as asbeshall be interpreted as the intersection of the pairwise absorption curves of the respectively uncoated and coated specimen of equal thickness. As soon as intersection occurs when approaching the absorption curve from higher to lower frequencies within the specified range, performance of the respectively coated device displays improved efficacy over the respectively uncoated analogue as to its low frequency absorption capacity. Data obtained for the above- mentioned specific examples ("coated") and comparative examples ("uncoated") are summarized in Table 1 . Because the above-mentioned edge and side effects are included, asmaxis labelled with an asterisk (*). Table 1 .

[0056] Counter intuitively and in contrast to the theory of panel absorbers, where a marked increase of the oscillating panels mass, that is for example compounding heavy plates usually made of high-impedance materials such as, for example, solid plastics, wood, or steel plates, while said steel plates, often galvanized, usually afford strengths of not less than about 0.2 to 1 ,5 mm, if steel plates are used, with the underlying acoustic foam, is stipulated in order to improve efficacy in the lower frequency range, the sound reduction device according to this invention unexpectedly, by not employing high impedance and high mass materials, exhibits a significant shift towards low frequency resonance absorption as to asmax, as100, as80and as50(cf. Table 1 and Fig. 1 ), by introduction of light and flexible membranes. Preferably, the sound reduction device may simply be adjusted by selecting appropriate dimensions and coating materials used as the skin to specifically tune absorption rates at approx. 80, 100, 125, 160, 200, 250, 315, 400, 500, and 1000 Hz up to not less than a minimum of asof 0.9, while the sound reduction device displays marked broadband efficacy with frequency dependent absorption coefficients, specifically at frequencies of 80, 100, 125, 160, 250, 315, 400, and 500 Hz that at least equal up to but usually exceed the performance of their respective uncoated analogues, while the sound reduction device outperforms their respective uncoated equivalents at least at 80, 100, 125 Hz with panel thicknesses greater than 40 mm. This is shown by the measurement data in Table 2. In the first column of Table 2 ("Type"), "c" stands for "coated", i.e. with skin and therefore according to the invention, whereas "u" stands for "uncoated", i.e. without skin and therefore not according to the invention. In the second column of Table 2, the thickness of the porous absorber according to the respective example ("c") or comparative example ("u") in millimetres is stated. In the further columns, the absorption coefficients measured at different frequencies are stated. Herein, if an absorption coefficient greater that 1 was measured due to edge and side effects, the value 1 .00 and the measured value are stated, the latter in parentheses and marked by an asterisk.

[0057] Table 2.

[0058] When using conventional porous absorbers, the sound reduction effect (i.e. the absorption coefficient) depends strongly on the distance between the porous absorber and the wall on which it is installed. The optimal distance is also strongly dependent on the frequency or wavelength of the sound. Therefore, it is often impossible to choose the optimal distance for a wide frequency spectrum.

[0059] It was found that with the above-described examples according to the present invention, this distance dependence may be significantly less pronounced or even absent. It is preferred that the distance of the sound reduction device according to the present invention from the wall on which it is installed has no or no technically significant influence on the sound reduction efficiency.

[0060] For example and without being bound to any theory, it is assumed that the reflection range and the resonance absorption range (cf. Fig 1 ) of the sound reduction device may be beneficially tuned by adjusting. Herein, adjusting may in particular be performed by a variation of (i) the panel thickness, (ii) the skin thickness, or (iii) both the panel thickness and the skin thickness. Herein, it is considered that increasing both parameters can for example shift the effective resonance absorption range towards lower frequencies while preferably improving the absorber’s performance characteristics in the required and targeted frequency range.

[0061] Preferably, the sound reduction device according to the invention is suitable for use in highly qualified environment requirements, such as cleanrooms, medical surroundings, food processing areas, meeting all required specifications up to cleanroom classes D, C, B, and / or A.

Claims

CLAIMS1 . Sound reduction device, comprising a porous sound absorber and a skin, wherein the porous sound absorber has a density of 0.3 g / cm3or less, wherein the skin is arranged on a surface of the porous sound absorber, and wherein the skin shields at least a portion of the surface of the porous sound absorber from the environment.

2. Sound reduction device according to claim 1 , wherein the porous sound absorber has a density of 0.001 g / cm3or more, preferably 0.005 g / cm3or more, more preferably 0.007 g / cm3or more and / or wherein the porous sound absorber has a density of 0.2 g / cm3or less, preferably 0.1 g / cm3or less, more preferably 0.05 g / cm3or less, most preferably 0.02 g / cm3or less.

3. Sound reduction device according to claim 1 or 2, wherein the skin encloses the porous absorbers.

4. Sound reduction device according to any of the preceding claims, wherein the skin is an elastic skin, preferably an elastic polymeric skin, most preferably an elastic polymeric foil.

5. Sound reduction device according to any of the preceding claims, wherein the porous absorber material comprises a material selected from the group consisting of foamed resin, foamed plastic, and acoustic foam.

6. Sound reduction device according to any of the preceding claims, wherein the porous absorber material comprises foamed melamine resin, in particular an open-cell melamine resin foam.

7. Sound reduction device according to any of the preceding claims, wherein the skin is wipeable and / or washable.

8. Sound reduction device according to any of the preceding claims,wherein the skin is essentially or entirely fluid-tight, in particular essentially or entirely gas-tight.

9. Sound reduction device according to any of the preceding claims, wherein the skin comprises a polymer, preferably a polymer selected from the group consisting of PE, PVC, PVF, PTFE, PDVC and PDVF.

10. Sound reduction device according to any of the preceding claims, wherein the skin is configured as a film having a thickness of 1 .0 mm or less, preferably 0.5 mm or less, more preferably 0.3 mm or less, most preferably 0.2 mm or less.11 . Sound reduction device according to any of the preceding claims, having a panel shape with two opposite main surfaces, wherein the area weight is 3 kg / m2or less, preferably 2 kg / m2or less, more preferably 1 .8 kg / m2or less, most preferably 1 .5 kg / m2or less, wherein each of the aforementioned area weights is calculated as the total mass of the sound reduction device divided by the area of the main surfaces.

12. Sound reduction device according to any of the preceding claims, wherein the sound reduction device has an absorption coefficient asof 0.9 or more at least at one frequency selected from the group consisting of 80, 100, 125, 160, 200, 250, 315, 400, 500, and 1000 Hz.

13. Sound reduction device according to any of the preceding claims, wherein at least at one frequency selected from the group consisting of 80, 100, and 125 Hz, the sound reduction device has an absorption coefficient aswhich is at least equal to, preferably higher than, asfor the porous sound absorber without the skin at the same frequency.

14. Sound reduction device according to any of the preceding claims, suitable for use under cleanroom conditions.

15. Sound reduction system comprising- a sound reduction device according to any of the preceding claims and- a fastener for fastening the sound reduction device to a supporting structure, wherein the fastener is immobilized on and / or in the sound reduction device, wherein preferably the fastener comprises a magnetic material, and / or wherein preferably the fastener comprises an adhesive.

16. Sound reduction system according to claim 15, wherein the fastener comprises a magnetic material which is embedded in the porous sound absorber or arranged on the porous sound absorber such that the skin shields the magnetic material from the environment.

17. System according to claim 15 or 16, suitable for use under cleanroom conditions.

18. Use of a porous sound absorber for sound reduction in an interior, preferably in a cleanroom, wherein the porous sound absorber has a density of 0.3 g / cm3or less, wherein a skin is arranged on a surface of the porous sound absorber, and wherein the skin shields at least a portion of the surface of the porous sound absorber from the environment.

19. Use according to claim 18, wherein the porous sound absorber has a density of 0.001 g / cm3or more, preferably 0.005 g / cm3or more, more preferably 0.007 g / cm3or more and / or wherein the porous sound absorber has a density of 0.2 g / cm3or less, preferably 0.1 g / cm3or less, more preferably 0.05 g / cm3or less, most preferably 0.02 g / cm3or less.

20. Use of a sound reduction device according to any of claims 1 to 14 or a sound reduction system according to any of claims 15 to 17 for sound reduction in an interior, preferably in a cleanroom.21 . Method of manufacturing a sound reduction device, in particular a sound reduction device according to any of claims 1 to 14, comprising the steps:- providing a porous sound absorber,- optinally, physically and / or chemically treating the porous sound absorber in order to reinforce the side surfaces and edges of the porous sound absorber,- surround the porous sound absorber by a skin material,- applying underpressure to the porous sound absorber surrounded by the skin material, and- sealing the skin material, wherein the porous absorber has a density of 0.3 g / cm3or less.

22. Method according to claim 21 , wherein the porous sound absorber has a density of 0.001 g / cm3or more, preferably 0.005 g / cm3or more, more preferably 0.007 g / cm3or more and / or wherein the porous sound absorber has a density of 0.2 g / cm3or less, preferably 0.1 g / cm3or less, more preferably 0.05 g / cm3or less, most preferably 0.02 g / cm3or less.

Images