FR2847919A1 - Double wall acoustic panel for absorbing includes spacing elements between absorber material and first of two acoustic walls, to create curtain of air between absorber and first wall - Google Patents

Abstract

The acoustic panel includes two walls (1,2) between which an acoustic absorber (3), such as glass wool, is disposed. The glass wool may be contained in a fine envelope e.g. formed from Mylar (RTM) material. Spacing elements (5) are disposed between the first wall and the absorber, so as to create a curtain of air between the absorber and the first wall.

Description

DOUBLE WALL ACOUSTIC PANEL

  The present invention relates to an acoustic panel with two walls between which is arranged an acoustic absorbent.

  In such a panel, the efficiency of the absorbent can be improved by creating an air space between the acoustic absorbent and the wall which receives the acoustic excitation.

  The present invention relates to an acoustic panel of the aforementioned type, the structure of which makes it possible to advantageously create this air space. 1o The invention thus relates to an acoustic panel comprising a first and a second wall between which is disposed an acoustic absorbent characterized in that, between the absorbent and the first wall, are arranged spacer elements distributed along at least one dimension and creating an air space between the absorbent and the first wall.

  More particularly, the spacing elements can form a two-dimensional network, for example a grid or a honeycomb or an embossing, or even pins distributed along these two dimensions.

  The grid, the honeycomb or the embossing can constitute a net 20 or a bag inside which the acoustic absorbent is placed. The bag can be embossed at least on one side facing the first wall. In particular, the net or the bag may be made of a thermally conductive material so that it constitutes a heat sink between said walls.

  A self-adhesive film carrying said network (for example grid, honeycomb, embossing and / or spikes) can be bonded either to the first wall or to the acoustic absorbent, in particular on a packaging of the acoustic absorbent. According to a preferred variant, the first wall has, on an internal face directed towards the acoustic absorbent, a plywood of a viscoelastic material and a covering comprising said spacing elements (for example parallel ridges, honeycombs, embossing, and / or spikes). Other characteristics and advantages of the invention will appear better on reading the description below, given by way of nonlimiting example, in conjunction with the drawings in which: - Figure 1 shows in exploded view a mode of carrying out the invention; - Figures 2A and 2B illustrate the conditions for implementing the invention; - Figures 3 to 8 illustrate variants of the invention; - Figures 9 to 12 are variants of the invention with the use of a viscoelastic material.

  In FIG. 1, the acoustic panel has a first wall 1 which receives the acoustic excitation (arrow F) when the panel is put in place, a second wall 2 and an acoustic absorbent 3, for example glass wool which can be contained in a thin envelope 4 in "Mylar" (Registered trademark of du Pont).

  The air gap is produced using a mechanical spacer constituted by a mesh 5.

  The shape of the mesh can be any, on the other hand its size must be such that under the action of the pressures which the absorbent undergoes, this must not exceed the surface defined by the mesh so that it cannot come into contact with wall 1 and that the air space keeps the desired thickness. FIG. 2A illustrates the case where, with the mounting pressure, the absorbent does not come into contact with the wall 1, FIG. 2B illustrating the unfavorable case of an overshoot beyond the grid 5.

  The nature of the material constituting the mesh is chosen according to the environmental constraints of the envisaged application. This material can be malleable to allow the mesh to conform to complicated shapes, provided that during deformation and under mounting or use pressures the absorbent cannot come into contact with the wall.

Example

  The absorbent 3 is low density glass wool 30 contained in a thin "Mylar" envelope (registered trademark). The spacer is a mesh of stainless steel wire 0.5 mm in diameter and whose mesh is a square of 10 mm side. The reduction in transparency is of the order of 3 to 4 dB.

  The grid 5, for example square (FIG. 3), can be replaced by a honeycomb 6 (FIG. 4) of suitable size. Too small a mesh leads to a large connecting surface between the excitation wall 1 and the absorbent 3, which decreases the performance.

  It is possible to replace the grid with pins 8 (FIG. 5) regularly distributed over the internal surface 11 of the wall 1 subjected to the excitation. This can be done using a self-adhesive film 9 on which these pins are already bonded. Alternatively, this film 9 can be just as well bonded to the absorbent 3 or its packaging 4 as there are for certain glass wools.

  However, care must be taken to avoid puncturing of the absorbent which would then favor its contact with the wall 1 receiving the excitation. The mesh 5 can constitute a net 7 in which the absorbent 3 is placed (FIG. 6).

  In certain applications, this net 7 can constitute a heat sink 15 which allows heat to be removed from one wall to the other while the absorbent generally constitutes a good thermal insulator. It suffices to manufacture the net 7 with a material which is a good conductor of heat, for example copper, aluminum. It is possible to increase the thermal performance by substituting the wire for the blades 5 ′ (FIG. 7) so as to have a larger contact surface without however greatly reducing the desired acoustic effect. The peripheral walls are formed by the lateral surface of the parallelepiped thus formed in which the absorbent is trapped. The thickness being small, the side is stiff when it is made of mesh 25 or of a ridge material, the net then becoming a cage. In this case, it constitutes a good solid-state passageway for vibrations and noise.

  The peripheral walls (noted, a b c d and e f g h in FIG. 6) can constitute a solid passageway if the material used for the net is of high modulus; in this case, this transmission will be limited by having large areas in one piece, to limit the effect of these peripheral walls. A bag 12 can be substituted for the net 7, the outer surface 14 of which is embossed at 15 (FIG. 8) so as to limit the contact surface with the excitation wall 1. The height of the embossed reinforcements 15 is determined to avoid contact of the outer face 14 with the inner face 11 of the wall 1 when the bag containing the absorbent is mounted with compression. According to another implementation of the invention, the plate 1 has on its internal face a plate of viscoelastic material 17 (for example the "deltane" material from the company PAULSTRA and a counter plate 17 'used to dampen vibrations of the plate 1 subjected to excitation. In this case, the counter plate 17 'is embossed. This configuration makes it possible to lighten the counter plate 17' by reducing its thickness while maintaining its stiffness by means of inertia. walls 18 perpendicular to its surface, which serve as spacers to avoid contact of the absorbent with the counterplate (FIG. 9).

  In the embodiments of FIGS. 9 to 11, the counterplate 17 ′ may have a bonded plate 20 carrying grooves 18 in one or two dimensions.

  In Figure 10, the spacers 18 are ribs formed in one dimension and spaced from each other, generally with a constant pitch.

  In FIG. 11, the ribs 18 (distributed in one or two dimensions) of the plate 17 ′ are wide enough for the plate of viscoelastic material to occupy the hollow part 19 thereof (see in particular the box in FIG. 1 1 ).

  Another variant uses a counter-plate 17 of reduced thickness, and it is stiffened by a grid 5 defined above, which is glued to the internal face of the counter-plate 17 'taking the precaution that the glue does not do not fill the mesh of the mesh in order to avoid contact with the acoustic absorbent (figure 12).

Claims (10)

  1) Acoustic panel comprising a first and a second wall between which is placed an acoustic absorbent s characterized in that, between the absorbent (3) and the first wall (1), are arranged spacer elements (5, 6 , 8, 18) distributed along at least one dimension and creating an air space between the absorbent (3) and the first wall (1). 2) Acoustic panel according to claim 1, characterized 1o in that the spacer elements (5, 6, 8, 18) form a two-dimensional network. 3) Acoustic panel according to claim 2, characterized in that said network comprises a grid, a honeycomb or an embossing.   4) Acoustic panel according to claim 3, characterized s5 in that the grid, the honeycomb or the embossing constitutes a net (7) inside which is placed the acoustic absorbent (3).   5) Acoustic panel according to claim 3, characterized in that it comprises a bag (14) in which the acoustic absorbent is disposed, this bag being embossed (15) at least on one side facing the first wall (1 ).   6) Acoustic panel according to one of claims 4 to 5, characterized in that said net or bag is made of thermally conductive material so that it constitutes a heat sink between said walls (1, 2).   7) Acoustic panel according to claim 2, characterized in that the network comprises pins (8) distributed along said two dimensions. 8) Acoustic panel according to one of claims 2 to 7, characterized in that it comprises a self-adhesive film (9) carrying said network, this film being bonded either to the first wall (1) or to the acoustic absorbent (3), in particular on a package (4) of the sound absorbent (3).   9) Acoustic panel according to one of claims 1 or 2, characterized in that the first wall has (1), on an internal face (11) directed towards the acoustic absorbent, a plate (17) of viscoelastic material and a counter -plate (17 ') carrying said spacer elements (5, 18).   10) Acoustic panel according to claim 9, characterized in that the counterplate (17 ') has an embossing (18) constituting said spacers or else has an embossed coating or a mesh.