FR2501887A1 - Low frequency sound absorber - has compressed multiple layer rolls of different materials formed as expanded mesh - Google Patents

Abstract

The sound absorber (1) is for low frequency noises and consists of layers of cut out and bent material - such as expanded metal (2). The different layers can be made of different types of materials. The materials used for the different layers can be composites such as plastics on metal. The layers can be made up into different structures. The sound absorber is made by compression of a roll (1) of material cut off and stretched. The rolls can be circular or quadrilateral in shape.

Description

ACOUSTIC ABSORBER
The present invention relates to an acoustic absorber, particularly suitable for absorbing sounds at medium and low frequencies.

 To absorb the sounds, it is known to use mineral wool or glass wool, but their maximum efficiency is in the high frequencies. In addition, they are sensitive to moisture and are ineffective when saturated with water.

Finally, they can not be used in all circumstances, especially when they are subjected to vibrations, which causes settlements.

 In order to be effective, a medium and low frequency sound absorber must have a relatively high density that the aforementioned materials do not have.

 An absorber consisting of a steel plate would respond to this condition, but it might resonate and reflect the sounds.

 On the other hand, metallic fibers would absorb sound effectively at medium and low frequencies, but these fibers have the disadvantage of being compressed by vibrations.

 A stack of layers of metal fabric would also be effective for the absorption of sounds at medium and low frequencies, but the layers, having no hold, would slide relative to each other in vertical use: we could not suspend them .

 The present invention relates to a sound absorber, particularly at medium and low frequencies, which is effective and has none of the disadvantages described above.

 The sound absorber according to the invention is characterized in that it consists of a stack of layers of cut and drawn materials or of deployed materials.

This stacking can be obtained by superposition of sheets, by winding to form a cylinder, or by folding accordion
The different layers may be made of materials of different materials or have different structures, especially with regard to the size of the stitches, the lar gear of the strips separating these stitches, or the thickness of the layers.

 To avoid the use, in some cases, of a system for connecting the different layers together, the stack can be compressed to obtain self-supporting pavers.

 By their structure, the layers of materials cut and stretched or deployed, fit into each other and form a very rigid assembly and insensitive to vibration holding is increased by compression.

 The sound waves that meet the absorber are not reflected; they are, on the contrary, trapped inside the absorber which is, therefore, very effective.

 The absorber can be adapted to the frequency of the sounds to be absorbed by varying the mesh size of the material cut and stretched or deployed, the width of the strips constituting these meshes, the thickness of the starting materials, the nature of the materials constituting the different layers, which may optionally be complexes formed of several materials, for example metal-elastomeric or plastic material, and on the pressure to which the stack is subjected.

An embodiment of the acoustic absorber according to the invention is described below, by way of nonlimiting example, with reference to the appended drawing in which:
Figure 1 is a perspective view of a strip of expanded metal,
Figure 2 is a section along II-II of Figure 1,
Figure 3 shows schematically a roll of expanded metal,
Figure 4 is a schematic sectional view of the absorber.

 As shown in the drawing, the acoustic absorber according to the invention is constituted from a stretched metal strip 1. This strip is formed of strips 2 which are corrugated zig-zag and integral with each other by their summits 3.

 Blle can be achieved, for example, by forming in a sheet metal strip slots arranged in staggered rows and then stretching the strip in a direction perpendicular to the slots and located in the plane of the sheet.

The tape 1 is then rolled, as shown in
Figure 3. Then the roller, being held laterally between two walls, is crushed as shown in Figure 4, so that the e roll takes a rectangular shape, its various turns 4a, 4b, 4c ... being compressed and s' nested in each other.

 It goes without saying that the present invention should not be considered as limited to the embodiment described and shown, but covers, on the contrary, all variants.

Claims (5)

 i. - Acoustic absorber, particularly medium and low frequency sounds, characterized in that it consists of a stack of layers of cut and stretched or deployed materials.  2. - Absorber according to claim 1, characterized in that the different layers of the stack are made of materials of different natures.  3. - Absorber according to claim 1 or 2, characterized in that the materials of the layers of the stack are complex products such as plastic or elastomer on metal.  4. Absorber according to one of claims 1 to 3 charac terized in that the different layers of the stack are of different structures.  5. - Absorber according to any one of claims 1 to 4, characterized in that it is formed by compression of a roll of a cut and stretched or unfolded material.