Sound-absorbing structure

Abstract

Sound-absorbing structure (1) comprising a first mesh layer (2) bonded to a second mesh layer (3) to form an inner perforated layer (6); an outer continuous layer (5); a plurality of spacers (4) arranged in contact with the outer continuous layer (5) and with the inner perforated layer (6) so as to keep them spaced apart from each other and define with them a plurality of cavities (19); wherein the holes (7) of the first mesh layer (2) are larger than the holes (8) of the second mesh layer (3); and wherein the inner perforated layer (6) is shaped so as to define a volume (V) within which a sound spreads.

Description

SOUND-ABSORBING STRUCTUREDESCRIPTIONTECHNICAL FIELD

[0001] The present invention relates to the field of sound-absorbing structures and structures suitable for attenuating or mitigating noise, in particular noise generated by an appliance, a machine or an electronic device.STATE OF THE ART

[0002] The state of the art includes various known solutions for effectively absorbing sound. The use of Helmholtz resonators to capture and dampen sound waves is known.

[0003] In particular, it is known to use sound-absorbing panels comprising a perforated panel behind which a honeycomb structure is arranged and, in turn, behind which a reflective panel is arranged, so as to create a plurality of Helmholtz resonators. The sound waves that enter through the holes are reflected by the reflective panel and, reflecting, enter into phase with the incoming wave, dampening it. In this way, the sound waves lose energy by converting into heat. The sound waves also remain trapped inside the cavities defined by the cells of the honeycomb structure and by the perforated and reflective panels. In this way the sound is absorbed by the sound-absorbing panel. Examples of this kind are described in patent documents US10971128B2 and WO2023169957A1.

[0004] The structures of these sound absorbing panels may include composite material elements, for example glass fiber or carbon fiber to make the reflective panel or perforated panel, as specified in document WO2023169957A1.

[0005] A further sound-absorbing panel is known from the patent document GB2130963A, which describes a panel comprising an air-permeable layer consisting of two fabric meshes impregnated, at the contact points, with resin and joined to a honeycomb, which in turn is joined to a continuous layer. This panel comprises a honeycomb inside, which, by its nature, has anticlastic properties. Therefore, if one tries to curve the honeycomb in one direction, the honeycomb curves in the opposite way along the transverse direction, assuming a shape similar to that of a saddle. It is therefore not possible to produce a cylindrical panel starting from the solution described in the document GB2130963A. Furthermore, this document describes a flat panel. From the solution ofthis document it is therefore not possible to obtain a prismatic structure that defines inside it a volume within which a device capable of generating noise can be placed.

[0006] One of the main problems of sound-absorbing panels that exploit the principle of Helmholtz resonators is their ability to adapt to complex shapes, such as very curved shapes or those with many undercuts.

[0007] Whenever an electrical, mechanical or electromechanical device produces a lot of noise, it's needed to absorb as much as possible the noise generated by it, but when the device has a complex shape, it is not always easy to create a covering for it that has sound-absorbing capabilities.

[0008] There is therefore a need to create in a simple and economical way sound-absorbing structures capable of absorbing the noise generated by noisy devices with curved or complex shapes. There is also a need to create sound-absorbing structures capable of covering noisy devices, without excessively increasing their dimensions.SUMMARY

[0009] These and other drawbacks of the prior art are now solved by a first object of the present invention which concerns a sound-absorbing structure comprising a first mesh layer constrained to a second mesh layer to form an inner perforated layer; an outer continuous layer; a plurality of spacers arranged in contact with the outer continuous layer and with the inner perforated layer so as to keep them spaced apart, in a fixed manner, and to define with them a plurality of resonant cavities. In particular, the holes in the mesh of the first mesh layer are larger than the holes in the mesh of the second mesh layer, and the inner perforated layer is shaped so as to define a volume within which a sound or noise spreads. Said volume is by its nature three-dimensional and is surrounded laterally by said inner perforated layer. The sound-absorbing structure thus conceived is made in layers and consequently the conformation of the same to complex surfaces or complex shapes is facilitated. The second mesh layer is used to allow sound waves to enter the soundabsorbing structure and acts as a resistive screen. While the first mesh layer, which is acoustically transparent, serves as a structural element of the so-called inner perforated layer. The outer continuous layer acts as a reflective surface for sound waves. Instead, the spacers allow for the definition of a plurality of resonant cavities together with the inner perforated layer and the outer continuous layer. The first mesh layer acts as a support to hold the second mesh layer. Furthermore, when the first mesh layer is arranged between the second mesh layer and the spacers, the first mesh layer can act as an interface to facilitate the union between the spacers and the second meshlayer. The inner perforated layer formed by the mesh layers is shaped to define a three-dimensional volume within which the source that generates the noise is arranged or through which the sound wave of the noise generating device passes. In essence, the inner perforated layer is shaped to form a compartment that is open at the top and bottom.

[0010] Preferably, the sound-absorbing structure comprises a closure configured to close at the top and / or bottom the cavity delimited internally by the inner perforated layer, externally by the outer continuous layer and laterally by the spacers. In this way, large resonant cavities are created inside the sound-absorbing structure, capable of absorbing a broad spectrum of noise frequencies, depending on the angle of incidence of the sound wave that penetrates the inner perforated layer. Therefore, the sound-absorbing structure thus conceived is capable of absorbing many frequencies and has a wide flexibility of use, for example in the case in which the noise source generates noise with variable frequency.

[0011] Advantageously, the sound-absorbing structure comprises transverse partitions configured to interconnect the spacers and divide said cavities into sub-cavities. These transverse partitions develop in a direction substantially orthogonal to that of the spacers so as to divide the cavity into smaller resonant cavities, capable of absorbing frequencies different from those of the cavity.

[0012] In particular, the inner perforated layer is a single body shaped to define a volume with a substantially prismatic shape. These volume shapes allow the device, that generates the noise to be absorbed, to be accommodated inside it. Furthermore, the inner perforated layer does not have any interruptions. The term "prismatic" or "prism" refers to a solid having equal bases, both circular or polygonal.

[0013] Preferably, the inner perforated layer is closed on itself so as to delimit the lateral surface of the volume. The inner perforated layer therefore represents a closed band capable of defining a volume and which is open above and below. This shape allows both to house inside the volume a device that generates the noise to be absorbed, or that the sound waves generated by the device cross the volume.

[0014] Advantageously, the outer continuous layer and the inner perforated layer are substantially parallel to each other so as to define resonant cavities of substantially constant thickness.

[0015] Preferably, the spacers are discrete elements, such as slats, arranged parallel to each other so as to act as reinforcing elements of the sound-absorbing structure.

[0016] In particular, the slats develop vertically along the height of the volume, making the soundabsorbing structure rigid and stable.

[0017] In particular, the first and second mesh layers can be connected to each other by a polymerizable resin, thus a resin capable of polymerizing, or by a glue. If the mesh layers are connected by a resin, when this polymerizes, the layers are monolithically connected to each other, forming the inner perforated layer.

[0018] Preferably, the resin / glue may be placed only at solid portions of the first mesh layer and permeates the second mesh layer where the solid portions of the first mesh layer overlap the second mesh layer. This arrangement of the polymerizable resin allows the two mesh layers to be joined without plugging the holes in the second mesh layer with resin, thus without plugging the holes in the fine mesh.

[0019] The first and / or second mesh layer can be made of fabric. Preferably the fabric can be made of fiberglass. In particular, the fabric of the first mesh layer is a loose mesh fabric, while the fabric of the second mesh layer is a tight mesh fabric. The use of a fabric for the first mesh layer allows the resin / glue to be absorbed without dispersing it. The resin therefore acts as a glue, as an alternative to normal adhesives. The use of a fabric also for the second mesh layer allows the first layer to easily connect to the second layer via the resin. The use of a fabric also allows for easy adaptability of the same to any shape. Finally, if the fabric is made of fiberglass, or alternatively carbon fiber, the structural resistance of the inner perforated layer improves once the resin polymerizes.

[0020] The inner perforated layer may comprise a third mesh layer having mesh holes larger than the mesh holes of the second mesh layer. The third mesh layer is arranged in contact with one of said first and second mesh layers. Preferably said third mesh layer may be bonded to the other mesh layer by said resin / glue. In this manner the layer that acts as an acoustic filter, thus the second mesh layer, is blocked between two large mesh layers that are acoustically transparent. The third mesh layer improves the structural resistance of the inner perforated layer when the resin polymerizes. Preferably the second mesh layer may be inserted between the first and third mesh layers.

[0021] The spacers can be made of a material compatible with said polymerizable resin. Preferably said spacers can be made of fiberglass. By making the spacers in a material compatible with that of the resin / glue, the adhesion is optimal. The use of polymerizable resin avoids the use of an adhesive that could block the holes of the mesh of the second mesh layer.

[0022] In particular, the outer continuous layer can be made of a material compatible with the polymerizable resin. Preferably, the outer continuous layer can be made of fiberglass. By making the outer continuous layer of a material compatible with that of the polymerizable resin, and in particular if it is made of fiberglass, the connection between the spacers and the outer continuouslayer can be made with a polymerizable resin similar to that used to connect the mesh layers. In this way, the use of an adhesive that could drip and block the holes in the mesh of the second mesh layer is avoided.

[0023] The sound-absorbing structure may comprise a further first mesh layer bonded to a further second mesh layer to form a further inner perforated layer. Said further inner perforated layer is arranged between said outer continuous layer and said inner perforated layer and spaced from them by means of spacers. This further inner perforated layer allows for the absorption of sound waves with frequencies different from those of the inner perforated layer and therefore further increasing the sound-absorbing capacity of the structure.

[0024] The sound-absorbing structure can have a cylindrical or prismatic shape and the spacers can be slats arranged parallel to the axis of said cylinder / prism. This conformation of the soundabsorbing structure is difficult to obtain with traditional structures that contain honeycombs, because the latter are anticlastic and do not allow them to be deformed to assume the shape of a cylinder or prism.

[0025] A second object of the present invention is a noise generating device which is coated with or comprises a sound-absorbing structure as defined above, and wherein the perforated layer is disposed towards the noise generating device or it is disposed at least partly within said volume. The sound-absorbing structure thus conceived may be used to coat a noise generating device to soundproof it or to soundproof an area of the device from which the noise exits.

[0026] These and other advantages will be explained in more detail in the description below of an example of implementation given for indicative and non-limiting purposes with reference to the attached drawings.DESCRIPTION OF THE DRAWINGS

[0027] In the drawings:Fig. 1 illustrates an exploded schematic view of a sound-absorbing structure according to the present invention;Fig. 2 illustrates a schematic front view of a sound-absorbing structure according to the present invention;Fig. 3 illustrates a schematic lateral sectional view of a first embodiment of the sound-absorbing structure according to the present invention;Fig. 4 illustrates an enlarged section of Fig. 3;Fig. 5 illustrates a schematic lateral sectional view of a second embodiment of the sound-absorbing structure according to the present invention;Fig. 6 illustrates a schematic lateral sectional view of a third embodiment of the sound-absorbing structure according to the present invention;Fig. 7 illustrates a schematic isometric view of a sound-absorbing structure according to the present invention;Fig. 8 illustrates an axonometric schematic view of a noise generating device comprising a soundabsorbing structure according to the present invention;Fig. 9 illustrates a top schematic view of a noise generating device covered by a sound-absorbing structure according to the present invention.DETAILED DESCRIPTION

[0028] The following description of one or more embodiments of the invention refers to the attached drawings. The same numerical references in the drawings identify equal or similar elements. The object of the invention is defined by the attached claims. The technical details, structures or characteristics of the solutions described below can be combined with each other in any manner.

[0029] In the figures, the reference number 1 indicates a sound-absorbing structure.

[0030] The sound-absorbing structure 1 is made up of three main elements: an inner perforated layer 6, an outer continuous layer 5 and a plurality of spacers 4 arranged between the inner perforated layer 6 and the outer continuous layer 5, to distance them from each other.

[0031] Through the holes of the inner perforated layer 6 the sound waves enter in spaces defined by the outer continuous layer 5, by the spacers 4 and by the inner perforated layer 6. These spaces constitute resonant cavities 19. The sound waves therefore bounce off the outer continuous layer 5 and, returning back, enter into phase with the sound waves entering through the holes of the inner perforated layer 6. In this way, the noise is dampened.

[0032] Spacers 4 are discrete elements separated and spaced from each other.

[0033] The inner perforated layer 6 is made up of two mesh layers 2, 3, thus two perforated layers.

[0034] A first mesh layer 2 has large holes 7 and is therefore substantially transparent to acoustic waves.

[0035] A second mesh layer 3, has narrow holes 8 and through these holes 8 the sound waves enter the cavities 19 that are located behind the inner perforated layer 6.

[0036] In particular, the interstitial holes 7 of the first mesh layer 2 are wider than the interstitial holes 8 of the second mesh layer 3, as clearly illustrated in Fig. 1 and 2.

[0037] In the following, the term "mesh layer" may be abbreviated to the term "layer", without changing its meaning.

[0038] The sound waves pass through the holes 8 of the second layer 3 and, once they enter in the cavities 19 defined by the inner perforated layer 6, the spacers 4 and the outer continuous layer 5, they are dampened.

[0039] The sound waves passing through the holes 8 of the second layer 3 can have a variable incidence. Depending on the incidence, the distance that the sound wave travels before hitting a spacer 4 or the outer continuous layer 5 is variable. In this way it is possible to absorb a broad spectrum of sound frequencies. This result is achieved thanks to the thin thickness of the second layer 3 and the large dimensions of the cavities 19 defined by the inner perforated layer 6, the spacers 4 and the outer continuous layer 5, compared to the dimensions of a honeycomb cell.

[0040] In a first embodiment, illustrated in Fig. 3, the first layer 2 with a large mesh is arranged towards the noise source which is located, or overlooks the volume V, and the second layer 3 with a fine mesh is arranged immediately behind the first layer 2.

[0041] The noise source is located within or faces the volume V defined by the shape of the inner perforated layer 6.

[0042] The inner perforated layer 6 can therefore be shaped like a cylinder, as illustrated in Fig. 9, or like a parallelepiped, as illustrated in Fig. 7. In this case, the parallelepiped can have rounded corners, as illustrated in Fig. 7. The volume V that is created inside the inner perforated layer 6 is therefore also shaped like a cylinder or parallelepiped, and can also have rounded corners. The inner perforated layer 6 always faces the volume V. Inside the volume V it diffuses the noise to be absorbed.

[0043] The resonant cavities 19 formed between the inner perforated layer 6, the spacers 4 and the outer continuous layer 5 can be divided into resonant sub-cavities 19' by one or more partitions 16 that develop transversely between one spacer and the other, as schematically illustrated in Fig. 2, in which, through the mesh layers 2 and 3, both the spacers 4 and the transverse partitions 16 can be seen.

[0044] In a further embodiment (not illustrated), the order of the layers is reversed, so that the second layer 3 with a fine mesh is closer to the noise source and, vice versa, the first layer 2 with a large mesh is set back behind the second layer 3.

[0045] The first layer 2 is bonded to the second layer 3, to form the inner perforated layer 6, by means of a polymerizable resin or a glue 9.

[0046] The polymerizable resin 9 is preferably a thermosetting resin, but may also be a UV resin, i.e. a resin that polymerizes when exposed to UV radiation.

[0047] The polymerizable resin 9 is a viscous resin with which the first layer 2 is soaked. Once the first layer 2 is soaked with resin 9, it is placed on the second layer 3. The resin 9 is by its nature sufficiently viscous not to permeate the entire second mesh layer 3, but rather to remain confined to the contact points between the two layers 2,3.

[0048] Glue 9 is also a dense glue, so that it does not permeate into the holes 8 of the second mesh layer 3.

[0049] The resin / glue 9 is in fact used to connect the mesh of the first layer 2 to the mesh of the second layer 3, but it must not block the holes 8 of the mesh of the second layer 3, otherwise the sound waves do not pass through the fine mesh of the second layer 3 and do not enter the soundabsorbing structure 1.

[0050] The resin / glue 9 is first positioned on the full portions of the mesh of the first layer 2 and then, once this is impregnated with resin / glue 9, the first layer 2 is placed in contact with the second layer 3 and the resin / glue that is on the full portions of the first layer 2 permeates into the mesh of the second layer 3 , as schematically illustrated in Fig. 3 and in the detail in Fig. 4. By choosing a sufficiently viscous resin / glue 9, the resin / glue 9 remains where the mesh of the first layer 2 overlaps the mesh of the second layer 3, without therefore closing the holes 8 of the mesh of the second layer 3.

[0051] If the resin / glue 9 slightly permeates the sides of the filled portions of the second mesh layer 3, most of the holes 8 of the mesh of the second layer 3 remain free and open, thus without compromising the filtering properties of the second mesh layer 3.

[0052] Once the first layer 2 is joined to the second layer 3, the resin 9 is polymerized or the glue 9 is dried, so as to solidify. The mesh of the first layer 2 thus becomes rigid, structurally supporting the second layer 3. Similarly, the joints between the first layer 2 and the second layer 3 also solidify, creating a firm anchoring between the two layers 2, 3. Conversely, the portions of the second layer 3 enclosed within the holes 7 of the mesh of the first layer 1 are not soaked in resin / glue and therefore do not solidify.

[0053] The inner perforated layer 6 thus obtained is rigid, and it has, within the holes 7 of the mesh of the first layer 2, portions of mesh with fine-mesh holes 8 which are permeable to sound.

[0054] Since the inner perforated layer 6 thus constituted is rigid, solid and structurally resistant, it can assume a closed shape such as a parallelepiped or a cylinder. The volume V assumes the shape defined by the internal surface of the inner perforated layer 6.

[0055] The spacers 4, which are preferably straight slats, are therefore arranged on the external surface of the inner perforated layer 6. The slats are arranged according to the height of the prism formed by the inner perforated layer 6.

[0056] Optionally, the mesh of the first and / or second layer 2,3 is formed by continuously winding threads around a rotating structure shaped like the shape that the mesh layer will take. The threads are first wound diagonally from bottom to top and then diagonally from top to bottom. In this way, a mesh is created in which the distance between the threads determines the size of the holes in the mesh. The threads can be pre-impregnated with resin before winding. In this way, it is possible to realize the inner perforated layer 6 as a single piece.

[0057] The spacers 4 are arranged on the external face of the inner perforated layer 6 in a parallel manner to each other.

[0058] Optionally, transversal partitions 16 can be joined, by means of resin / glue 9, to the inner perforated layer 6 and, at their ends, to the spacers 4, as illustrated in Fig. 2.

[0059] Above the spacers 4 and the transverse partitions 16, if present, the outer continuous layer 5 is arranged. In this way, a three-dimensional structure of the type illustrated in Fig. 7 and 9 is created.

[0060] The first and second layers 2, 3 are preferably made of fabrics with warp and weft such as to create wider meshes for the first layer 2 and narrower meshes for the second layer 3. Preferably, the fabrics that can be used are leno and double weft fabrics. In particular, the fabrics can be made of glass fiber or carbon fiber.

[0061] The fabrics of the first and second layers 3, joined together and with the resin / glue 9 not yet solidified, can be arranged on the surface of the device 10 to adapt to its external shape. Once the resin 9 polymerizes or the glue 9 dries, the inner perforated layer 6 thus obtained has a prismatic shape that conforms to that of the device 10.

[0062] Alternatively, the device 10 that generates the noise to be absorbed can be arranged inside the volume created by the inner perforated layer 6.

[0063] The spacers 4 can be straight slats, as illustrated in Fig. 1, 2, 3, 5, 6, 7 and 9.

[0064] The spacers 4 are placed in contact with the inner perforated layer 6 and joined to it.

[0065] If the spacers 4 are made of a material compatible with the resin 9, such as glass fiber, the spacers 4 can be joined to the inner perforated layer 6 without the need for glue, but rather by using the resin 9 before it polymerizes. In this way, once the resin 9 solidifies, the first layer 2, the second layer 3 and the spacers 4 remain monolithically connected to each other.

[0066] The outer continuous layer 5 is then placed in contact with the spacers 4 and the same resin / glue 9 used to connect the first and second layers 2, 3 together can be used to join the spacers4 to the outer continuous layer 5. This bond is particularly strong when the outer continuous layer5 is made of fiberglass and a resin 9 is used.

[0067] The outer continuous layer 5 is a rigid and impervious layer.

[0068] For simplicity, a flat sound-absorbing structure 1 is illustrated in Figs. 1, 2, 3, 5 and 6, but, as illustrated in Figs. 8 and 9, any shape can be easily obtained by means of the structure 1 thus conceived. The sound-absorbing structure can, for example, assume a curved shape. In this case, the mesh layers 2 and 3 have a curved shape, as well as the outer continuous layer 5.

[0069] In a second embodiment, illustrated in Fig. 5, there are two large mesh layers and the second mesh layer 3 is arranged between the first layer 2 and a further layer similar to the first, called the third layer 13. The third layer 13 has holes 14 in the mesh having substantially the same size as the holes 7 in the mesh of the first layer 2. The third mesh layer 13 is arranged in contact with the second mesh layer 3, but could be arranged in contact with the first mesh layer 2. The third mesh layer 13 is connected to the other mesh layers 2,3 with the same glue resin 9. By using two large mesh layers, the inner perforated layer 6 is structurally more resistant.

[0070] In a third embodiment, illustrated in Fig. 6, the sound-absorbing structure 1 is composed of multiple layers, and in particular, an inner perforated layer 6 may be arranged between two sets of spacers 4. In practice, the sound-absorbing structure 1 comprises a first inner perforated layer 6, followed by a first layer of spacers 4, in turn followed by a further inner perforated layer 6' and then by a second layer of spacers 4, and finally by an outer continuous layer 5. The spacers 4 may have different heights, i.e. thicknesses, in order to dampen different frequencies. By increasing the height, lower sound frequencies are absorbed. Conversely, higher frequencies are absorbed if the height is reduced. By arranging multiple sets of perforated layers 6,6' and spacers 4 in series, it is also possible to absorb sound waves more effectively, even if the overall thickness of the soundabsorbing structure 1 deteriorates. Each further inner perforated layer 6' includes a further first mesh layer 2' and a further second mesh layer 3'.

[0071] The sound-absorbing structure 1 thus conceived is suitable for assuming a cylindrical shape. The volume V that is created inside the inner perforated layer 6 has a cylindrical shape. The soundabsorbing structure with a cylindrical shape is suitable for wrapping a device 10 having a cylindrical shape as illustrated in Fig. 9. In this case, the device 10 is connected to the inner perforated layer 6 via connecting elements 18. In this embodiment, the spacers 4 are arranged parallel to the axis of the cylinder. Finally, on the external surface of the spacers 4, the outer continuous layer 5 is also arranged with a cylindrical shape, as illustrated in Fig. 9. The outer continuous layer 5 is therefore parallel to the inner perforated layer 6. The mesh of the first layer 2 is therefore open towards the device 10, in order to best collect the sound waves and the noise generated by the latter. The sound waves generated by the device 1, passing through the second layer 3, enter the cavities 19 defined between the outer continuous layer 5, the spacers 4 and the inner perforated layer 6, and are damped in these cavities 19. These cavities 19 can be closed above and below by a closure 17, schematically illustrated, only in part, in Fig. 9.

[0072] Instead of wrapping the device 10, as in Fig. 9, the cylindrical sound-absorbing structure 1 can be arranged on the casing 12 of a different device 11 that does not have a cylindrical shape. In the case illustrated in Fig. 8, the device 11 is the external exchanger of an air conditioner and the part from which the noise comes out is the opening of the fan 15.

[0073] By arranging the sound-absorbing structure coaxial with the rotation axis of the fan 15, the sound-absorbing structure 1 acts like the silencer of a muffler for the sound waves coming from the opening of the fan 15, dampening the noise produced by the device 11.

[0074] In Fig. 7, a sound-absorbing structure with a prismatic shape is illustrated, in particular a parallelepiped shape with rounded corners. The first layer 2 faces a volume V in which the noise to be absorbed diffuses. The second layer 3 is connected to the first layer 2 and, on the latter, straight slats parallel to the axis of the volume V are connected which, that act as spacers 4. Finally, the outer continuous layer 5 is arranged on the spacers 4. In this embodiment of the sound-absorbing structure 1, as in the previous ones, the volume V has open bases. Optionally, these bases can be closed by caps (not illustrated) which in turn have sound-absorbing properties. This structure 1 can be obtained by continuously winding threads so to obtain monolithic layers 5,6.

[0075] In conclusion, it is clear that the invention thus conceived is susceptible to numerous modifications or variations, all falling within the invention; furthermore, all the details are replaceable by technically equivalent elements. In practice, the quantities may be varied according to technical needs.

[0076] Numerical references legend:1 sound-absorbing structure2 first mesh layer2' further first mesh layer3 second mesh layer3' further second mesh layer4 spacer5 outer continuous layer6 inner perforated layer6' further inner perforated layer7 hole (of the first mesh layer)8 hole (of the second mesh layer)9 resin / glue10 cylindrical device11 non-cylindrical device12 device casing13 third mesh layer14 hole (of the third layer mesh)15 fan16 partition17 closure18 connecting element19 cavity

Claims

CLAIMS1. Sound-absorbing structure (1) comprising:- a first mesh layer (2) bonded to a second mesh layer (3) to form an inner perforated layer (6);- an outer continuous layer (5);- a plurality of spacers (4) arranged in contact with the outer continuous layer (5) and with the inner perforated layer (6) so as to keep them spaced and define with them a plurality of cavities (19); wherein the holes (7) of the first mesh layer (2) are wider than the holes (8) of the second mesh layer (3); and wherein the inner perforated layer (6) is shaped so as to define a volume (V) within which a sound spreads.

2. Sound-absorbing structure (1) according to claim 1, further comprising at least one closure (17) suitable for closing said cavities (19) at the top and / or bottom.

3. Sound-absorbing structure (1) according to claim 1 or 2, comprising transverse partitions (16) configured to connect the spacers (4) to each other and divide said cavities (19) into sub-cavities (19').

4. Sound-absorbing structure (1) according to any one of the preceding claims, wherein the inner perforated layer (6) is a single body shaped so as to define a volume (V) having a substantially prismatic shape.

5. Sound-absorbing structure (1) according to any one of the preceding claims, wherein the inner perforated layer (6) is closed on itself so as to delimit the lateral surface of said volume (V).

6. Sound-absorbing structure (1) according to any one of the preceding claims, wherein the outer continuous layer (5) is shaped so as to be substantially parallel to the inner perforated layer (6).

7. Sound-absorbing structure (1) according to any one of the preceding claims, wherein the spacers (4) are discrete elements, such as slats, arranged parallel to each other.

8. Sound-absorbing structure (1) according to claim 7, wherein the slats develop according to the height of the volume (V).

9. Sound-absorbing structure (1) according to any one of the preceding claims, wherein the first and second mesh layers (2, 3) are bonded together by a polymerizable resin or a glue (9).

10. Sound-absorbing structure (1) according to claim 9, wherein the resin / glue (9) is arranged only at solid portions of the first mesh layer (2) and permeates the second mesh layer (3) where the solid portions of the first mesh layer (2) overlap the second mesh layer (3).

11. Sound-absorbing structure (1) according to any of the preceding claims, wherein the first and / or second mesh layer (2, 3) is a fabric, preferably made of glass fiber.

12. Sound-absorbing structure (1) according to any one of the preceding claims, wherein the inner perforated layer (6) comprises a third mesh layer (13), having the holes (14) larger than the holes (7) of the second mesh layer (2), arranged in contact with one of said first and second mesh layers (2, 3), preferably said third mesh layer (13) is bonded to the other mesh layer (2, 3) by means of said resin / glue (9).

13. Sound-absorbing structure (1) according to claim 12, wherein the second mesh layer (3) is arranged between the first and third mesh layers (2, 13).

14. Sound-absorbing structure (1) according to any of the preceding claims dependent on claim 9, wherein the spacers (4) are made of a material compatible with said resin / glue (9)15. Sound-absorbing structure (1) according to claim 14, wherein said one or more spacers (4) are made of fiberglass.

16. Sound-absorbing structure (1) according to claim 14 or 15, wherein the outer continuous layer (5) is made of material compatible with said resin / glue (9), preferably the outer continuous layer (5) is made of fiberglass.

17. Sound-absorbing structure (1) according to any one of the preceding claims, comprising a further first mesh layer (2') bonded to a further second mesh layer (3') to form a further inner perforated layer (6'); wherein said further inner perforated layer (6') is arranged between said outer continuous layer (5) and said inner perforated layer (6) and spaced from them by said spacers (4).

18. A noise generating device (10, 11) coated with or comprising a sound-absorbing structure (1) according to any one of claims 1 to 17, wherein the inner perforated layer (6) is arranged towards the noise generating device (1).