SOUND ABSORBER

Abstract

The present application relates to a sound absorber (1) for acoustic shielding, comprising a planar base body in which several strip-shaped sections (2a) are formed parallel to one another, each of the strip-shaped sections (2a) having two opposite edges and at least one recess (4) extending along the strip-shaped section (2a), which projects from the planar base body and through which an opening (5) with side edges (6a, 6b) is formed at each of the opposite edges. The recess (4) has an edge (4a) extending transversely to the strip-shaped section (2a) and is subdivided by the edge (4a) along the strip-shaped section (2a) into a first recess area (4b) with first side edges (6a) and a second recess area (4c) with second side edges (6b). The first side edges (6a) are curved differently than the second side edges (6b).

Description

TECHNICAL AREA

[0001] The present invention relates to a sound absorber for acoustic shielding. BACKGROUND

[0002] Conventional airborne sound absorbers predominantly use open-cell foams or artificial mineral fibers (also known as MMF) as inexpensive and flexible damping materials. They are often used as sheet material in wall linings, baffle silencers, or sound enclosures and require cover plates, such as those made of wood, perforated sheet metal, or a metal mesh, for support, stiffening, and protection. These cover plates should have the largest possible perforation area (δ), meaning the area of ​​the holes relative to the total surface area. Only when δ is greater than 30% can the incident sound waves penetrate the cover plates unhindered and reach the underlying sound-absorbing material, where they are absorbed by friction in the pores or at the fibers, i.e., converted into heat. The holes in the cover plates play essentially no acoustic role, as the cover plates merely provide mechanical support for the airborne sound absorbers behind them.

[0003] These conventional airborne sound absorbers, also known as porous absorbers, are heavy, very energy-intensive to manufacture, difficult to reuse or recycle, and always require a supporting structure and a sound-permeable covering (e.g., coarsely perforated panel or textile), resulting in a high overall weight and space, assembly, and planning requirements.

[0004] For several years now, there has been an increasing demand, especially from the automotive and construction industries, for abrasion-resistant absorber materials that do not fray, do not absorb liquids, do not mold, prevent bacterial growth, do not thermally insulate but are able to thermally shield, and are non-flammable.

[0005] Against this background, microperforated panel absorbers, hereinafter also referred to as MPA, were developed from sheet metal, plexiglass, or fabric. Their acoustic effectiveness is based on the frictional forces in the perforations, which are designed as holes and slots. These perforations, together with the air cushion behind them, form a resonance system and therefore function without additional damping materials in the cavities behind them. In this sense, they are also a (Helmholtz) resonator, which additionally possesses viscous friction in the micro-holes. However, unlike a classic Helmholtz resonator, MPA do not require a closed volume, but interact with a sound-reflective surface, often a rear wall.

[0006] Since the material properties of the panels and substructures have no significant influence on absorption, microperforated absorbers can be manufactured from any material adapted to the respective operating conditions, such as steel, stainless steel, aluminum, plastic, wood, or fabric. This allows existing structural components to be activated as microperforated acoustic panels (MPAs). Therefore, MPAs fundamentally represent a way to meet the aforementioned requirements, particularly from the automotive and construction industries.

[0007] Sheet metal MPA components with pierced damping holes can become blocked or torn during forming, weakening their acoustic and mechanical function and potentially rendering them unusable. In contrast, MPA in the form of microperforated fabric absorbers can be formed easily, but their production is expensive. The acoustic function is also weakened if the perforations become blocked by particles.

[0008] Plate-shaped absorbers for acoustic shielding, in particular MPA, are known, for example, from DE 74 24 983 U, DE 10 147 645 A1, DE 10 345 575 B3, DE 297 22 367 U1, DE 10 2004 019 055 A1, DE 10 2004 039 706 B3, DE 10 2005 058 251 A1, EP 0 876 539 B1, EP 2 256 722 A1, GB 1 015 984 A, or GB 1 039 544 A.

[0009] Porous absorbers, for example those made of foam, wool, and / or metal, especially in the form of fibers or wires, require a precise thickness for installation. Optimal results are achieved when the porous material is positioned at a specific distance from a sound-reflective wall, so that the sound waves strike the wall during operation and are reflected back. Within the porous material, the sound energy is then converted into heat through friction of the air vibrations against the porous material. Since optimal absorption based on friction occurs where the air vibrations have the highest velocity, areas where the vibrations are slower can be omitted with only a slight loss of effectiveness, thus conserving material.

[0010] While porous absorbers have very small openings where viscous friction can occur, MPA (multi-layer acoustic membrane) has significantly larger openings. However, the mass-spring principle works in their favor here. The vibration of the MPA increases the air velocity in the openings, so that the greater frictional force compensates for the lower viscous friction. Depending on the frequency to be absorbed, the distance to the sound-reflective wall must therefore be maintained very precisely. The frequency-dependent absorption resembles a bell curve and can be shifted by changing the distance to the sound-reflective wall.

[0011] With increasing resistance, which can be generated by smaller volumes, smaller gaps, and increased airflow, the frictional velocity of the mass-spring principle decreases, leading to a reduction in the absorption rate and a simultaneous broadening of the absorbed spectrum. The optimal diameter of the openings therefore lies in a range between 0.1 mm and 0.4 mm.

[0012] High frequencies diffract less and are therefore more easily blocked by obstacles. This means that low tones can be heard around corners and over objects, while high tones are more readily perceived in a direct line of sight to the sound source. Porous absorbers or increased mass / inertia offer little resistance to low frequencies. Therefore, microplastics (MPAs) are typically used to absorb low frequencies. For this purpose, they require a significant distance from the sound-reflective surface.

[0013] Combining MPA with porous absorbers allows for some of the advantages of these concepts regarding sound absorption. However, MPA also loses some of its advantages and inherits some of the disadvantages of porous absorbers, particularly its tendency to fray, absorb liquids, mold, not prevent bacterial growth, lack thermal insulation, and be flammable. Therefore, it is often better to use pure MPA to fully exploit its benefits. Manufacturing MPA from a single material not only makes it suitable for retrofitting existing structures but also opens up numerous additional applications, such as thermally active surfaces for heating, cooling, electrostatic attraction, safety coverings, protective covers, lightweight construction elements, and much more.

[0014] Sheet metal MPAs are usually manufactured using expensive precision tools, energy-intensive laser processes, or other costly methods. Furthermore, production is often slow because the precision tools can deform and require repair or replacement. However, precision tools are often necessary to minimize production errors, as MPAs are generally visible and must therefore meet high aesthetic standards. To keep manufacturing costs as low as possible, the sheet thickness is typically very thin (<0.5 mm), and low-strength metals are used. Such MPAs often require a supporting structure and cannot replace existing load-bearing elements. Additionally, thin sheets offer only minimal sound insulation, meaning that thin MPAs do not optimally prevent sound transmission. Cleaning an MPA can also pose a challenge.

[0015] With sufficient material thickness, MPA are self-supporting, so no support structure is required and they can replace existing components equivalently. PRESENTATION OF THE INVENTION

[0016] In light of the above, one object of the present invention is to provide a sound absorber that offers high and broadband sound absorption in the range of human hearing and has the simplest possible structure.

[0017] Another aspect of the object of the invention is to provide such a sound absorber which is also as abrasion-resistant as possible and / or does not fray and / or does not absorb liquid and / or does not mold as much as possible and / or prevents bacterial growth as much as possible and / or is not thermally insulated as much as possible, but is able to provide thermal shielding as much as possible, and / or is non-combustible.

[0018] Another aspect of the object of the invention is to provide such a sound absorber which also offers high structural stability and is therefore highly resilient and deformable without relevant loss of its effectiveness, in particular pierceable, trimmable and cleanable, and which can therefore also serve as a protective shield against flying parts on a machine, for example a shredder, milling cutter, rotor frame or saw.

[0019] Another aspect of the object of the invention is to provide a sound absorber that can be used under the highest pressure conditions in close proximity to sound sources such as a combustion chamber, a furnace, a turbine, a pump, a compressor, a pipeline or an outlet opening in gaseous or liquid media.

[0020] The problem is solved by a sound absorber according to claim 1. Advantageous embodiments of the invention are described in the dependent claims.

[0021] A sound absorber according to the present invention for acoustic shielding comprises a planar base body in which several strip-shaped sections are formed side by side, preferably parallel to each other, each strip-shaped section having two opposing edges extending along the strip-shaped section, between which a depression projects from the planar base body. The depression is formed along and between the edges of each of the strip-shaped sections in a wave-like manner with at least two valleys and a peak between them, whereby at least one opening with side edges is formed at each of the opposing edges.

[0022] In this context, "acoustic shielding" means that the energy of the incident sound waves is partially absorbed, so that the transmitted and / or reflected sound waves have lower energy and therefore a lower volume. Thus, the sound absorber can be used both to shield sound sources from the outside and to reduce sound reflection from flat surfaces. Furthermore, the sound absorber can also contribute to thermal insulation. At the same time, the device can be made of a material that allows heat conduction.

[0023] In this context, "planar" means that the dimensions of the basic body in an essentially two-dimensional plane are larger, in particular at least one order of magnitude larger, than perpendicular to it, whereby the plane may also be curved or kinked if necessary.

[0024] In this context, "strip-shaped" means that the length of the sections is preferably much greater than their width, in particular at least twice as great, where the directional term "along the section" or "along the extent of the strip-shaped section" refers to the longitudinal direction, i.e., the direction of the length of the strip-shaped section. The edges of the strip-shaped sections form the geometric boundaries of the sections without requiring any additional shapes or material properties. Alternatively, the strip-shaped section can also have a comparable, in particular the same, width as its length, although it is preferred that the length of the sections be much greater than their width.

[0025] Several strip-shaped sections are preferably arranged one behind the other along their length and alternatively or additionally side by side transversely to their length. In the case of strip-shaped sections arranged one behind the other, the strip-shaped sections are separated from each other by essentially flat areas of the base body from which the recesses protrude.

[0026] In this context, a "depression" refers to a region of the strip-shaped section where the material of the base body is separated from the surrounding material at both edges and, at its ends, rejoins a plateau at the same level as the surrounding material, thus merging with it. The material therefore extends out of the plane of the planar base body, the plateau, and back into the plane, while separating from it at the edges of the depression, thereby creating the openings.

[0027] Preferably, there is no gap between the depressions and the material adjacent to them perpendicular to the length of the strip-shaped sections, so that, for example, the peak(s) of the depression rest directly against the adjacent material. This clamps the peak(s) between the adjacent sections, thus damping vibrations and offering greater resistance. Alternatively, a gap can be provided between the depressions and the material adjacent to them perpendicular to the length of the strip-shaped sections, which can have a sound-absorbing effect. In this case, it is also possible for sections of the depression to vibrate more strongly and thus act as resonators, as will be explained in more detail below. For this purpose, for example, the peak(s) can be indented in the middle perpendicular to the length of the strip-shaped sections, so that gaps open up on both sides.

[0028] It is also possible that the mountain(s) do not extend to the height of the material adjoining the strip-shaped sections perpendicular to their extent, so that the depressions adjacent to the mountain each form a long opening on the opposite edges, the extent of which is reduced by the mountain(s) but not interrupted. The mountain(s) can also extend up to and even beyond the material adjoining the strip-shaped sections perpendicular to their extent, thus separating the openings on the opposite edges and forming a further opening above the material adjoining the strip-shaped sections perpendicular to their extent.

[0029] A characteristic feature of the "mountain" shape is a semicircular or crescent-shaped area on the back of the sound absorber, extending from the direction in which the valleys extend to the direction in which the mountain(s) extend. This area appears as a light reflection with a curvature, the open end of which points towards the mountain. In embodiments with multiple mountains within the depression of the strip-shaped section, this area can also exhibit curvature in both directions, so that it can have the shape of two crescents or semicircles pointing away from each other.

[0030] Such a sound absorber can achieve high and broadband sound absorption within the range of human hearing, and it also has a simple structure, as it can be manufactured from a single flat base. This simple structure allows for particularly cost-effective production, especially compared to sound absorbers that have multiple layers of the same or, more importantly, different materials.

[0031] The sound absorber can be made from a material that is abrasion-resistant, does not fray, does not absorb liquid, does not mold, prevents bacterial growth, is not thermally insulating but is capable of thermal shielding, and is non-combustible. However, sound absorbers not made from such a material can also conform to the invention and achieve the desired high and broadband sound absorption within the range of human hearing and also outside of human hearing, adapted to a desired target spectrum.

[0032] Furthermore, the sound absorber can be designed to offer high structural stability and be deformable without significant loss of effectiveness, in particular being pierceable, trimmable and cleanable, and can also be used as a protective cover or the like.

[0033] The geometry of the recess causes incident sound to be advantageously deflected through the opening beneath the sound absorber, thus achieving absorption. Essentially, the sound absorber is effective from both sides; that is, depending on the installation situation, the openings also serve to deflect sound from the underside to the top of the sound absorber.

[0034] The effects of this sound absorber can include, in particular, the fact that the incident sound is guided through the openings at the opposite edges and, depending on the design of the sound absorber, especially the existence and arrangement of further openings or other recesses, can lead to resonance effects or anti-sound effects, for example.

[0035] Preferably, each of the strip-shaped sections has several successive peaks along the strip-shaped section between the valleys of the depression. This increases the effectiveness of the sound absorber. It is further preferred that at least some of the openings of one of the strip-shaped sections are opposite at least some of the openings of at least one adjacent strip-shaped section.

[0036] This configuration of openings allows the previously mentioned anti-noise effect to be used particularly effectively, namely when the sound through opposing openings of adjacent strip-shaped sections interferes with itself and cancels itself out.

[0037] In a preferred embodiment, at least one, preferably two, of the valleys, namely the one located at the beginning or end of the depression, or the one located at both the beginning and end of the depression, has an edge extending transversely to the strip-shaped section, wherein the valley, preferably the valleys, of the depression are subdivided by the edge along the strip-shaped section into a first valley region with first side edges and a second valley region with second side edges. The first side edges are curved differently than the second side edges. The edge extends substantially between the two side edges transversely to the extent of the strip-shaped section.

[0038] In embodiments with multiple peaks in the depression, the valleys between two peaks preferably do not have such an edge. In other words, the valleys between two peaks are preferably edgeless along the extent of the strip-shaped section.

[0039] The fact that the first edges are curved differently than the second edges can mean, in particular, that they differ in their curvature profile. For example, the first edges might be concave and the second edges flat or convex, the first edges convex and the second edges flat or concave, or the first edges flat and the second edges concave or convex, or both the first and second edges convex. Combinations of these curvatures along the edges can also be a significant factor in whether the first edges are curved differently than the second edges.

[0040] The edge running perpendicular to the strip-shaped section can be sharp or rounded. For a rounded edge to be considered an edge within the meaning of the present invention, the radius of curvature of the edge must be smaller than that of the recessed areas and / or the edge is located at the deepest point of the recess. However, several edges running perpendicular to the strip-shaped section can also occur in one of the recessed valleys.

[0041] Advantageously, the first side edges are convexly curved and the second side edges are concavely curved.

[0042] While a concavely curved edge facilitates sound radiation into the opening even at extreme angles, the opposite is true for a convexly curved edge. This allows sound waves, preferably those originating from a concavely curved edge, to flow unimpeded into the opening, creating a constantly increasing resistance similar to that of a wing. A preferred asymmetrical opening geometry enables particularly broadband sound absorption.

[0043] The first valley section is advantageously convex. Alternatively or additionally, the second valley section is advantageously concave.

[0044] In this context, "curved" means that the curved areas are not only bent longitudinally along the strip-shaped section, but also transversely in a second direction, creating a multidimensional, trough-like bulge. While a "convex" bulge is "bulged outwards," a "concave" bulge is "bulged inwards." The bulge may also partially overlap with the material adjoining it transversely to the length of the strip-shaped sections.

[0045] An additional curvature of the curved areas reinforces the effect described above in connection with the concave and convex curved side edges, thereby further improving the sound absorption of the device.

[0046] In a preferred embodiment, the crest(s) of the depression are convexly curved, while the valleys of the depression are concave and convexly curved. In embodiments with multiple crests of the depression, the first or last valley of the depression, preferably both the first and last valleys, are concavely and convexly curved, while the valley or valleys between two crests of the depression are concavely curved, but may also be convexly curved. This feature can be recognized, among other things, by the fact that a crescent shape, particularly with a curved edge and a straight edge, may appear in the valleys on the back side of the sound absorber due to light reflection.

[0047] Preferably, the strip-shaped sections are arranged directly next to each other, and the valleys of the depressions of adjacent strip-shaped sections are offset from each other. Alternatively, a strip-shaped intermediate section is preferably arranged between two adjacent, side-by-side, and especially parallel, strip-shaped sections.

[0048] By selectively dimensioning the depth of the depressions and / or a cavity behind them, as well as the relative arrangement of the openings by offsetting or parallelizing the strips, material overlaps by arranging several plates on top of each other, and thus shifting the positions of the openings of the individual plates relative to each other, the above-described effect of greater resistance can be increased without changing the size of the openings themselves.

[0049] In the case of directly adjacent strip-shaped sections with staggered depressions featuring peaks and valleys, the openings are each bounded at the top by a peak of the adjacent strip-shaped section, with valleys extending along the strip-shaped section in front of and behind it. Thus, the same section forms both valleys that deflect sound laterally towards the adjacent strip-shaped section and openings that receive sound arriving laterally from the adjacent strip-shaped section, further improving sound absorption per unit area. Furthermore, under a peak, the sound waves arriving from both sides generate anti-sound, at least partially canceling out the opposing sound waves and further enhancing the sound-absorbing effect of the sound absorber.

[0050] In the case of the flat intermediate sections arranged between the strip-shaped sections, the openings are each bounded at the top by the adjacent flat intermediate section. Such a geometry has higher stiffness and is simpler and more cost-effective to manufacture. In this configuration, it is also preferable to arrange the openings parallel to each other, rather than offset, in order to effectively utilize the active noise cancellation principle.

[0051] It is advantageous to arrange several flat sound absorbers towards each other as a backdrop, or to shape a sound absorber so that the flat intermediate sections can also act as a sound-hard wall.

[0052] In a preferred embodiment, the sound absorber has several consecutive holes along the strip-shaped intermediate sections. Holes can also be formed along the strip-shaped section, particularly on the peak(s) or peaks, or on the valleys or on the plateau between successively arranged strip-shaped sections, among other things to save weight or to achieve higher sound transmission of the sound absorber, for example, if a porous sound absorber is located behind it.

[0053] The holes can be circular or strip-shaped. The cut-out material can be flanged perpendicular to the flat base. This allows the cut-out material to act as a closer, sound-reflective wall, spacer, or diffuser, particularly as a room divider, thus increasing the broadband response of the sound absorber. Additionally, the flanged cut-out material can be angled again at its end. This allows for increased flow resistance at high flow velocities, further improving the sound absorber's absorption capacity at these speeds.

[0054] The holes can also be positioned to locally reduce the stiffness of the sound absorber, thereby locally influencing its elasticity and vibrational properties. This allows for the creation of properties similar to a vibroacoustic metamaterial, also known as a VAMM, which can be used for the targeted absorption of sound within a specific frequency range. Despite their lack of mass, vibroacoustic metamaterials allow for the creation of one or more stopbands through the arrangement of periodic resonators or vibration elements, further enhancing sound insulation.

[0055] Preferably, the strip-shaped sections or the intermediate sections, or both, have the same width. Preferably, the width is in the range of 2 mm to 6 mm, and particularly preferably in the range of 3 mm to 5 mm. These parameter ranges have proven to be particularly suitable with regard to the structural stability of the sound absorber, while simultaneously achieving good broadband sound absorption through the overlap of two bell curves. Alternatively, the strip-shaped sections or the intermediate sections can also have varying and different widths.

[0056] It is also possible to increase the width of the peak(s) and / or valleys of the depression so that they extend beyond the adjacent material perpendicular to the length of the strip-shaped section. This allows the openings to be enlarged. This can be achieved, for example, by narrowing the depression in the thickness direction through the application of pressure, which can cause the material to deflect laterally perpendicular to the length of the strip-shaped section.

[0057] It is also possible to taper the material along the depression from above and / or below, thereby controlling the direction of sound propagation.

[0058] Preferably, the strip-shaped sections or intermediate sections, or both, have a thickness in the range of 0.02 mm to 3 mm, and preferably in the range of 0.8 mm to 2 mm. A thickness of 0.02 mm can be achieved, for example, with a thin film, while greater thicknesses can be achieved, for example, with a sheet. A thickness tolerance of 0.2 mm can be assumed for a sheet. Ideally, the thickness is such that the sound absorber is self-supporting, i.e., it does not require an additional structural element to maintain its shape. These parameter ranges have proven particularly suitable with regard to the structural stability of the sound absorber, while simultaneously achieving good broadband sound absorption in the relevant frequency range.In embodiments with intermediate sections, the thickness of the strip-shaped sections is preferably somewhat less than the thickness of the strip-shaped intermediate sections. This allows the strip-shaped intermediate sections to fulfill a stabilizing function while simultaneously maintaining high elasticity in the strip-shaped sections.

[0059] Preferably, the openings have the same height. The height is preferably in the range of 0.1 mm or greater and / or 0.5 mm, or less, particularly preferably in the range of 0.05 mm or greater and / or 0.4 mm or less, and most preferably is 0.22–0.25 mm.

[0060] Openings with geometries in the preferred areas are particularly well-suited for absorbing sound waves across a broad spectrum of human hearing. Furthermore, openings of the same size and geometry are easy and inexpensive to manufacture. Alternatively, however, it can also be advantageous to provide openings with different geometries, especially different heights, for example, to further improve the broadband sound absorption. It is particularly preferred to provide opposing openings directly or via a strip-shaped intermediate section of adjacent strip-shaped sections of the same height. By varying the distance between opposing openings of adjacent strip-shaped sections, the absorption spectrum of the sound absorber, especially the frequencies of maximum absorption, can be influenced.

[0061] The strip-shaped sections can be arranged in a non-parallel relative arrangement, preferably in a wave-like, trapezoidal, or circular shape. This allows the distances between opposing openings of adjacent strip-shaped sections to vary regularly, thus improving the broadband sound absorption.

[0062] In a particularly preferred sound absorber, the ratio of the opening length to the thickness of the respective strip-shaped section is between 1.0 and 5.8 for a thickness of 1.0 mm or more, and between 1.0 and 5.0 for a thickness of 0.2 mm or more and less than 1.0 mm. This ratio results in particularly good broadband sound absorption. This takes into account, on the one hand, the shadowing of the recess by the base material and its influence on the size of the opening. On the other hand, it ensures simple manufacturability of the sound absorber and, in particular, the openings.

[0063] In a preferred embodiment, in which a strip-shaped intermediate section is arranged between each of two strip-shaped sections, the intermediate section is bent along its strip-shaped course at its edges facing the strip-shaped sections in the direction of the recesses to form a third side edge of the openings. The height of the openings is in the range of 0.05 mm to 0.5 mm, particularly preferably in the range of 0.2 mm to 0.4 mm, and is preferably 0.3 mm. The bent area can be of the same or different dimensions. It is possible that the bent area is bent first upwards and then downwards. It is possible that the bent area ends at the same height along the edge or terminates in a stepped or sloping manner at different heights relative to the intermediate section.

[0064] The angled intermediate section ensures that even with very thin base bodies, the openings are not too tall and therefore remain effective. Furthermore, the angled shape helps to increase the effectiveness of the sound absorber. The surface created by the angled edge can be not only perpendicular to the intermediate section, i.e., parallel to the opening, but can also have other angles, for example, 45 degrees towards the strip-shaped section or towards the intermediate section, i.e., away from the strip-shaped section, or it can be angled multiple times.

[0065] Preferably, the sound absorber is coated, in particular galvanized, zinc-plated, tin-plated, aluminized and / or covered with a porous lacquer layer or with a phosphate layer.

[0066] This allows the sound absorber to be used as an aesthetically pleasing component even in environments where the appearance of a surface is important, without compromising its effectiveness. This is not the case for many conventional sound absorbers, as a coating clogs the technically necessary pores or perforations. A suitable coating can also further improve sound absorption, for example, by creating a rougher surface that reflects sound less strongly. Furthermore, a coating can contribute to the device's longevity.

[0067] In a preferred embodiment, the base body has several freely vibrating tabs. Preferably, these tabs are arranged at regular intervals. Preferably, the tabs are arranged within the recess. In particular, the tabs have a tapered section by which they are connected to the flat base body. This feature also allows the sound absorber to additionally function as a VAMM (Vibrationally Active Material Flow). VAMM is characterized, among other things, by having resonators at regular intervals that can vibrate. This prevents the propagation of bending waves in the material. A stopband is created, i.e., a frequency range in which vibrations are absorbed. This also reduces the transmission of sound within the frequency range of the stopband.The tabs can be positioned in various locations and can be created by cutting or removing square or otherwise shaped pieces of material, straight or angled, at multiple points and in different forms. The resulting freely vibrating tab can then function as a resonator. Alternatively, cuts can be made around one or more recesses in the sound absorber, so that the enclosed area of ​​material is connected to the rest of the base body at only one point.

[0068] The recessed strip-shaped sections can have a cut through the material running transversely or obliquely to the length of the strip-shaped section, thus dividing the recess into two separate parts. This allows for particularly high elasticity of the two parts of the recess, resulting in a freely vibrating resonator or two freely vibrating resonators, and thus enabling the sound absorber to be used as a VAMM (Variable Airflow Module). For this purpose, it can be particularly advantageous to provide a varying thickness along the freely vibrating part of the strip-shaped section in order to influence the resonance properties of the sound absorber.

[0069] Along the length of the strip-shaped section towards the cut, the thickness of the base material can decrease asymptotically. Thus, vibrations of the material towards the cut can lead to an almost complete absorption and conversion of the energy of the incident sound. In this way, the sound absorber can assume and utilize the properties of an acoustic black hole (ASL).

[0070] The recess can be long and feature one or more peaks. A longer recess with multiple peaks results in greater elasticity of the resonator. In the case of external forces acting on the recess, such as centrifugal or kinetic forces like wind, the height of the openings can change dynamically. This can be significant, for example, when the sound absorber is used in a rotor. In the case of a rotor, the sound absorber can be arranged and designed so that the height of the openings, determined by the rotational speed, adapts to the frequency to be absorbed, which is determined by the rotor's rotational speed. Due to its high elasticity, the openings are also particularly easy to clean.

[0071] Several successive peaks and valleys within a depression form a spring-like structure, whereby, under sufficient tension, sound energy striking the structure is transferred across the entire surface of the sound absorber and propagated through all its contours. An angled orientation of sections of the structure relative to the direction of sound propagation can also lead to material savings.

[0072] It is possible to stack several sound absorbers on top of each other to enhance their sound-absorbing effect. These absorbers can be arranged in a straight line or offset from one another. The peaks and valleys of the recesses in the multiple absorbers can be of equal or different sizes. Additional recesses can also be designed to act as spacers between adjacent absorbers and as vibration dampers.

[0073] Stacking multiple sound absorbers on top of each other can create a sound absorber with significantly improved aerodynamics. The distance between stacked sound absorbers, as well as the angle at which they are positioned relative to each other, can be varied. In particular, the stacked sound absorbers can be encased in a rubber band or frame.

[0074] Preferably, the sound absorber is combined with other, especially porous, sound absorbers, such as rock wool, metal fibers, foam, or PET, and arranged as a sandwich component. It is particularly preferred if the sound absorber has the aforementioned holes in the strip-shaped intermediate sections and / or the strip-shaped sections themselves. It is further preferred to deform the sound absorber as a whole, for example, as a trapezoidal sheet, corrugated sheet, or the like, and for this purpose, or alternatively, to deform one or more of the strip-shaped intermediate sections.

[0075] Additionally, it is preferred to create a cavity in front of or behind the sound absorber, viewed in the direction of sound propagation, to further enhance its effectiveness. The heights of the openings, the dimensions of the peaks and valleys, the shapes of the side edges, and other elements can vary, particularly in their dimensions. This increases the broadband capability of the sound absorber, meaning it performs well across a wider frequency spectrum.

[0076] Furthermore, it is possible to apply an adhesive or a viscous compound, which may contain particles such as small spheres, to the base body of the sound absorber. The adhesive or viscous compound can be applied to the strip-shaped intermediate sections, to the peaks or valleys, or between successively arranged strip-shaped sections on the base body, or it can be placed between peaks and valleys and the edges of the recess. The adhesive or viscous compound can thus function as a vibration damper.

[0077] It is also possible to completely or partially close the openings along one of the two opposite edges, so that the openings of adjacent strip-shaped sections point towards each other. It is also possible for the openings of adjacent strip-shaped sections to point in the same direction. In this case, it is further preferred to make the valleys on the side of the completely or partially closed openings somewhat shallower, thus forming a flow channel running obliquely to the flat base body, which enhances the sound-absorbing effect of the sound absorber. By using openings of varying depths, the resistance to sound propagation can be adapted to the specific installation situation and thereby optimized.

[0078] The sound absorber can also fulfill other functions. In particular, it can be used as an inlay or as a raised floor.

[0079] The sound absorber can also be used as a cooling element. The shape can, alternatively or additionally to its acoustic shielding effect, facilitate efficient heat transfer to a fluid, particularly a gas or liquid. For example, a fluid can flow from one side of the flat base into the peaks or valleys and through the openings to the other side. The peaks and valleys create a protected pressure zone in which thermal energy can be transferred very efficiently to the flat base.

[0080] The sound absorber can preferably also be used in an exhaust gas catalyst of an internal combustion engine, particularly of a motor vehicle. The claimed shape can, alternatively or additionally, serve as a suitable support for exhaust gas catalyst structures, in addition to its acoustic shielding effect.

[0081] The sound absorber can preferably be used as a structural element in lightweight construction. Its stressed shape can impart particularly high strength to the base body. This stressed shape can also be used as a load-bearing element in lightweight construction, either as an alternative or in addition to its acoustic shielding function.

[0082] Further advantages and developments of the invention will result from the following description of the figures and the entirety of the claims. SHORT FIGURE DESCRIPTION

[0083] Further features and advantages of the device and the method will become apparent from the following description of embodiments with reference to the accompanying drawings. These drawings show: Fig. 1. A perspective view of a known acoustic shielding device Fig. 2a a perspective view of a first embodiment of a preferred sound absorber Fig. 2b an enlarged section from Fig. 2a Fig. 2c an enlarged section from Fig. 2b Fig. 3a a perspective view of a second embodiment of a preferred sound absorber Fig. 3b an enlarged section from Fig. 3a Fig. 3c an enlarged section from Fig. 3b Fig. 4a a perspective view of a third embodiment of a preferred sound absorber Fig. 4b an enlarged section from Fig. 4a Fig. 4c an enlarged section from Fig. 4b Fig. 5a a perspective view of a fourth embodiment of a preferred sound absorber Fig. 5b an enlarged section from Fig. 5a Fig. 5c an enlarged section from Fig. 5b Fig. 6a a perspective view of a fifth embodiment of a preferred sound absorber Fig. 6b an enlarged section from Fig. 6a Fig. 6c an enlarged section from Fig. 6b Fig. 6d the fifth embodiment from a different perspective than Fig. 6a-6c Fig. 7a a perspective view of a sixth embodiment of a preferred sound absorber Fig. 7b an enlarged section from Fig. 7a Fig. 7c an enlarged section from Fig. 7b Fig. 8a a perspective view of a seventh embodiment of a preferred sound absorber Fig. 8b an enlarged section from Fig. 8a Fig. 8c an enlarged section from Fig. 8b Fig. 9a a perspective view of an eighth embodiment of a preferred sound absorber Fig. 9b an enlarged section from Fig. 9a Fig. 9c an enlarged section from Fig. 9b Fig. 10a a schematic side view of the opening in the first embodiment of a preferred sound absorber Fig. 10b a schematic side view of the opening in a further embodiment of a preferred sound absorber Fig. 10c a schematic side view of opposite openings of a preferred sound absorber Fig. 11a an arc-shaped curve Fig. 11b a bell-shaped curve Fig. 12 a sound absorption diagram of a preferred sound absorber in the frequency range of human hearing Fig. 13 an enlarged section of a depression with a mountain and two valleys from a back side of the sound absorber Fig. 14 an enlarged section of the depression from Fig. 13 from a front of the sound absorber WAYS TO IMPLEMENT THE INVENTION

[0084] Identical reference symbols listed in different figures name identical, corresponding, or functionally similar elements.

[0085] Fig. Figure 1 shows a perspective view of a device for acoustic shielding known from GB 1 039 544 A. The openings in the sheet 20 are produced by shearing and bending to form a plurality of curved ribs 22, i.e., protrusions and depressions, which are bent upwards and downwards from the sheet plane in alternating horizontal rows 23 and 24, i.e., strip-shaped sections.

[0086] Fig. Figures 2a to 2c show perspective views of a first embodiment of a preferred sound absorber 1 for acoustic shielding at various magnifications.

[0087] The sound absorber 1 can absorb sound waves that are perpendicular or at an angle to the surface. Fig. 2a. The sound absorber 1 can also absorb sound waves that strike the side shown above. However, the sound absorber 1 can also absorb sound waves that strike the side shown in 2a perpendicularly or at an angle. Fig. 2a, the side shown below, i.e., its back. Furthermore, the sound absorber 1 also offers a certain degree of thermal shielding in both directions.

[0088] Fig. Figure 2a shows the sound absorber 1 with a planar base body that extends essentially along a horizontal plane. Within this base body, several strip-shaped sections 2a are formed parallel to each other, each with depressions that run in a wave-like pattern along a first direction and are arranged parallel to each other in a second direction, as described in more detail below. Fig. 2b is shown.

[0089] In this context, "horizontal" refers only to the plane depicted in the drawings. The sound absorber 1 can assume any orientation in the room and can also have a curved, bent, or otherwise non-horizontal shape. "Wavy" in this context means that the depressions of sections 2a have peaks 3 (corresponding to wave crests) and troughs 4 (corresponding to wave troughs) that project or recede from each other in a third direction perpendicular to the horizontal plane, and the peaks 3 and troughs 4 may have different shapes relative to each other.

[0090] In the embodiment shown, all recesses of sections 2a along the first direction have the same wave pattern. However, they can also have different wave patterns. In this context, the "wave pattern" refers to the shape and arrangement of the peaks 3 and valleys 4 in the recess.

[0091] Fig. 2b shows an enlarged view of the in Fig. 2a of the sound absorber 1 shown. The wave pattern of the depressions of sections 2a comprises alternating arc-shaped mountains 3 with a first length La and plateaus 3a with a second length Lb, wherein the mountains 3 are separated from the plateaus 3a by valleys 4 with an edge 4a. The edge 4a divides the valley 4 into a first valley area 4b with first side edges 6a and a second valley area 4c with second side edges 6b, which are in Fig. 2c are shown in more detail.

[0092] In this context, "arc-shaped" means that the curvature in the first direction is strictly negative, i.e., that mountain 3 is only curved outwards, as in Fig. 11a is shown. In this context, "bell-shaped" means that the curvature in the first direction is initially positive, then negative, and then positive again; that is, that mountain 3 is curved inwards at the sides and outwards in the middle, as also shown in Fig. 11b is shown.

[0093] Alternatively, the wave patterns of the depressions can also consist of only arc-shaped mountains 3, only bell-shaped mountains 3, another sequence of arc-shaped and bell-shaped mountains 3, rounded valleys 4, triangular, square, pentagonal, polygonal or trapezoidal mountains 3 or valleys 4, or any combination thereof.

[0094] In the illustrated embodiment, all recesses of sections 2a have the same constant width B in the second direction and the same constant thickness D in the third direction. A "constant thickness" is also present if the thickness varies slightly due to manufacturing processes, e.g., crushing during stamping, or for other reasons, by up to 20% of the thickness D or, in particular, 0.2 mm. A "constant width" is also present if the width varies slightly due to manufacturing processes or for other reasons, by up to 20% of the width B. Alternatively, the width B or the thickness D can also vary within sections 2a and / or between sections 2a.

[0095] The mountains 3 and valleys 4 of the depressions of two adjacent sections 2a are offset in the first direction, so that the sections 2a abut each other in some places in the second direction and are separated from each other by openings 5 ​​in other places. The offset is alternating, so that the sections 2a adjacent to each other on both sides of a section 2a are arranged identically, with mountains 3 and valleys 4 facing each other.

[0096] Alternatively, only every third, every fourth, or even none of section 2a can be arranged in the same way. In an alternative embodiment, in which each hill 3 is offset from, i.e., not directly opposite, a valley 4, the openings 5 ​​have an even more asymmetrical shape, which can have an advantageous effect on broadband sound absorption.

[0097] Fig. 2c shows an enlarged view of the in Fig. 2b shown sound absorber 1. The two valleys 4 of the depression form an opening 5 at each edge to an adjacent section 2a. The height H of the opening 5 corresponds to its greatest extent in the third direction perpendicular to the planar base body, while the length Lc of the opening 5 corresponds to its greatest extent in the first direction along the strip-shaped sections 2a.

[0098] The opening 5 is formed by the first side edge 6a and the second side edge 6b of a first section 2a in the area of ​​a valley 4, in Fig. 2c below, as well as by a third side edge 6c of an adjacent second section 2a, in Fig. 2c above, bounded so that it has a triangular shape. The corner of the opening 5 between the side edges 6a and 6b is formed by the edge 4a of the valley.

[0099] While the side edges 6a, 6b, 6c of sections 2a facing opening 5 are not rounded and thus have a very small radius of curvature, the side edges 7 of the respective sections 2a facing away from opening 5, in particular the upwardly projecting outer edges 7, can be rounded and thus have a larger radius of curvature than the side edges 6a, 6b, 6c facing opening 5. This allows the sound to flow in a controlled manner into valley 4.

[0100] Furthermore, sections 2a may have convex bulges 8a at the edges of the mountains 3, i.e., outwardly curved three-dimensional trough-shaped mountains, and concave bulges 8b at the edges of the transitions of the valleys into the plateau 3a, i.e., inwardly curved three-dimensional trough-shaped valleys.

[0101] Fig. 3 shows analogous to Fig. 2 another preferred embodiment of a sound absorber 1. In contrast to the embodiment according to Fig. 2 indicates the in Fig. In the embodiment shown in Figure 3, strip-shaped intermediate sections 2b are provided between the strip-shaped sections 2a. The intermediate sections 2b are flat, i.e., they do not have any depressions with valleys 4 or mountains 3.

[0102] Fig. 4 shows analogous to Fig. 3 another preferred embodiment of a sound absorber 1. In contrast to the embodiment according to Fig. 3 the mountains 3 are designed in such a way that they extend beyond the strip-shaped intermediate sections 2b and the plateau 3a, thus creating openings 5 ​​also on the top of the sound absorber 1, which additionally contribute to the effectiveness of the sound absorber 1.

[0103] Fig. 5 shows analogous to Fig. 3 another preferred embodiment of a sound absorber 1. In contrast to the embodiment according to Fig. 3 are three mountains 3 along the depression of each of the strip-shaped sections 2a formed as a continuous wave, whereas in the embodiment according to Fig. 3 only one mountain 3 along the depression of each of the strip-shaped sections 2a was formed as a wave. Between the mountains 3 formed as waves, plateaus 3a are formed as flat sections continuous with the adjacent intermediate sections 2b.

[0104] Fig. 6 shows analogous to Fig. 3 another preferred embodiment of a sound absorber 1. In contrast to the embodiment according to Fig. 3. The thickness of the base body is considerably smaller. To nevertheless ensure an effective size of the openings 5, the strip-shaped intermediate section 2b is chamfered along its strip-shaped course at its edges facing the strip-shaped sections 2a in the direction of the valleys 4 to form the third side edge 6c of the openings 5, so that the height H of the openings 5 ​​lies in a range of 0.1 mm to 0.5 mm, particularly preferably in a range of 0.2 mm to 0.4 mm, and preferably is 0.3 mm. The fact that the edges are chamfered can be seen particularly in Fig. 6d clearly recognizable.

[0105] Fig. 7 shows analogous to Fig. 3 another preferred embodiment of a sound absorber 1. In contrast to the embodiment according to Fig. The intermediate sections 2b have holes 9 arranged consecutively along them. These holes 9 further increase the effectiveness of the sound absorber 1.

[0106] Fig. 8 shows analogous to Fig. 3 another preferred embodiment of a sound absorber 1. In contrast to the embodiment according to Fig. 3. The strip-shaped sections 2a and the strip-shaped intermediate sections 2b are narrower, i.e., they have a smaller width B.

[0107] Fig. 9 shows analogous to Fig. 2 another preferred embodiment of a sound absorber 1. In contrast to the embodiment according to Fig. In Figure 2, the strip-shaped sections 2a are arranged at right angles to each other. As a result, the depressions of some of the strip-shaped sections 2a align along one direction along the planar base body as shown in Figure 2. Fig. 2 is formed, wherein three strip-shaped sections 2a, i.e., their depressions, are always arranged next to each other. Then depressions of strip-shaped sections are formed perpendicular to them along the planar base body. Overall, the depressions of strip-shaped sections, arranged alternately at right angles to each other, form an interrupted striped pattern.

[0108] Fig. 10a and Fig. Figure 10b shows schematic side views of an opening 5 in two different embodiments of a preferred sound absorber 1 in the X / Z plane. In both embodiments, the triangular opening 5 is bounded downwards by the sloping and curved side edges 6a, 6b of the valley 4 and hill 3 of the first section 2a, respectively. The opening 5 is bounded upwards in Fig. 10a through the curved third side edge 6c of an adjacent second section 2a and in Fig. 10b is bounded by the straight third side edge 6c of an adjacent intermediate section 2b.

[0109] The first section 2a exhibits different curvatures at the side edges 6a, 6b of the valley 4 and mountain 3, respectively, which form the lower edges of the opening 5. While section 2a is convex (i.e., curved outwards) in the region of the first side edge 6a, it is concave (i.e., curved inwards) in the region of the second side edge 6b. Alternatively, the first section 2a may only be curved in this way in the region of one of the two side edges 6a, 6b, while remaining straight in the region of the other side edge 6a, 6b.

[0110] In the first embodiment, the upper edge of the opening 5 is formed by the third side edge 6c of a hill 3 of the adjacent strip-shaped section 2a and is therefore curved. In the second embodiment, the upper edge of the opening 5 is formed by the third side edge 6c of the adjacent flat intermediate section 2b and is therefore straight.

[0111] In embodiments with several mountains 3 in the depression, between which valleys 4 are arranged, there need not be an edge 4a, but rather a continuous transition between the curvature of the side edges 6b and 6a is possible. Alternatively, it is also possible to provide the edge 4a, so that the curvatures of the side edges 6a, 6b in these valleys always correspond to the curvature of the side edge 6a in Fig. 10a and Fig. 10b. It is also possible that the curvature of the side edges 6a, 6b in these valleys always follows the same path as side edge 6b.

[0112] Fig. Figure 10c shows a schematic side view of openings 5 ​​in a preferred sound absorber 1 in the Y / Z plane, i.e., looking along the strip-shaped sections 2a or intermediate sections 2b. In the region of the valley 4, the first sections 2a are designed such that incident sound waves S are deflected laterally through the openings 5 ​​under the respective adjacent strip-shaped sections 2a or intermediate sections 2b.

[0113] Since a strip-shaped section 2a with a valley 4 is arranged on both sides of the strip-shaped sections 2a and the intermediate sections 2b, the sound waves S flow through the openings 5 ​​from both sides under the strip-shaped section 2a and the intermediate section 2b, where they meet, interfere with each other, and are at least partially absorbed by friction. The preferred triangular shape of the openings 5, the sound deflection, and the sound interference enable high sound absorption and broadband capability.

[0114] Besides the in Fig. In addition to the embodiment shown in Figure 10c, embodiments are also possible in which the area below the strip-shaped sections 2a or intermediate sections 2b is closed not only at the top but also at the bottom, thereby reducing the transmission of sound waves through the sound absorber 1. Such an embodiment could, for example, be produced by additive manufacturing processes.

[0115] Fig. 11a and Fig. Figure 11b schematically shows two types of curves, where Fig. 11a an arc-shaped curve and Fig. Figure 11b shows a bell-shaped curve. "Arc-shaped" in this context means that the curve corresponding to a peak 3 of the sound absorber 1 has a strictly negative curvature. That is, the peak only curves outwards. "Bell-shaped" in this context means that the curve corresponding to a transition to the plateau 3a of the sound absorber has first a positive, then a negative, and then a positive curvature again.

[0116] Fig. Figure 12 shows the sound absorption of a preferred device of the second embodiment in the frequency range of human hearing, as determined by an impedance tube measurement according to EN ISO 105345-1 at a distance of 5 cm from the sound-reflective wall. While the dashed line represents human hearing for different frequencies, the solid line shows the absorption of the sound absorber for the respective frequencies according to the aforementioned measurement. The frequency range absorbed by the sound absorber corresponds very well to the frequency range of human hearing, meaning that good and broadband sound absorption is achieved in the relevant frequency ranges. Two bell curves are visible, which are very close to each other and overlap, demonstrating a broadband absorption effect.The distance between the peaks of the bell curves can be changed, for example, by varying the distance between the opposite openings of the strip-shaped sections. Furthermore, the entire spectrum can be shifted along the x-axis by using a sound-reflective wall, whereby the distance of the sound absorber to the sound-reflective wall, which could be a side wall, for example, is varied.

[0117] Fig. 13 and Fig. Figure 14 shows an enlarged section of a depression with a hill 3 and two valleys 4. These two illustrations clarify the curvature of the depression. While the hill 3 is slightly convex, the two valleys are convex and concave. The transition between the convex curvature 8a and the concave curvature 8b in the valleys 4 is at edge 4a.

[0118] This creates a surface gradient on the back of the sound absorber in the area of ​​the edges 4a of the valleys 4, which appears crescent-shaped due to light reflection and points with open ends towards the mountain 3. REFERENCE MARK LIST 1 sound absorber 2a strip-shaped section 2b strip-shaped intermediate section 3 Mountains 3a Plateau 4 Valley 4a Edge 4b first valley area 4c second valley area 5 Opening 6a first side edge 6b second side edge 6c third side edge 7 outer side edges 8a convex curvature 8b concave curve 9 holes B Width Thickness Total thickness (dt) The first length Lb second length Lc length H height S sound waves X first direction Y second direction Z third direction QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 74 24 983 U

[0008] DE 10 147 645 A1

[0008] DE 10 345 575 B3

[0008] DE 297 22 367 U1

[0008] DE 10 2004 019 055 A1

[0008] DE 10 2004 039 706 B3

[0008] DE 10 2005 058 251 A1

[0008] EP 0 876 539 B1

[0008] EP 2 256 722 A1

[0008] GB 1 015 984 A

[0008] GB 1 039 544 A [0008, 0085]

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