EP1407091B1 - Sonic absorption device for premises - Google Patents

Abstract

The invention concerns a sonic absorption device for acoustic correction of premises or for soundproofing of boxes designed to be arranged in front of a support wall delimiting the premises or the box. It consists of a sparsely perforated embossed sheet (1) reflecting actively acoustic waves and of a porous sound absorbing material layer (2) arranged against said plate (1) between the latter and the support wall. Advantageously, the sonic absorption device is arranged at a distance from the support wall so as to provide a gas space between the sound absorbing material layer (2) and the support wall. The invention enables to obtain uniform absorption characteristics for a whole range of audio frequencies.

Description

The present invention relates to the design and manufacture of acoustic absorption devices for the acoustic correction of premises or the soundproofing of caissons or casings of noisy machines. Such a device is to be arranged in front of a support wall delimiting the room or box.

Acoustic absorption devices known and as described, for example, by the document FR 2,632,672 , have the disadvantage that their absorption capacity is not uniform for the entire range of sound frequencies. Large depressions are observed in the absorption characteristic curve.

The invention therefore proposes to provide absorption devices of the aforementioned type whose characteristic curve is substantially equal performance level for a range of predetermined frequencies, and more particularly in the range of audible frequencies.

For this purpose, the device according to the invention comprises in combination a perforated embossed sheet active in reflection acoustic waves and a layer of porous absorbent material which is fixed glued against said sheet so as to be disposed between the latter and the support wall. The layer of porous material strongly dampens the resonances, so that the characteristic curve of the absorption capacity of the device as a whole is smoothed.

Advantageously, the absorption device is disposed at a distance from the support wall so as to provide an air gap between the absorbent material layer and the support wall. One of the major advantages of the invention is here to lead to sound wave absorption elements that are easily parameterizable according to the sound spectrum to be corrected, by playing on the respective thicknesses of the air gap and the layer: of absorbent which separates it from the reflective sheet.

According to a preferred embodiment of the invention, the perforations of the sheet: embossed are slots arranged in regular mesh as in an expanded metal plate.

Advantageously, the porous absorbent material is of the cellular type, such as a melamine or polyurethane foam. According to another embodiment, generally equivalent to the previous one, the porous absorbent material is a felt, in particular based on natural or artificial fibers, especially based on glass wool or rockwool.

Advantageously, the thickness of the layer of porous absorbent material is between 5 and 200 mm and the thickness of the embossed sheet is between 0.5 and 1.5 mm.

According to another characteristic of the invention, the perforated embossed sheet is bonded to the layer of porous material so as to constitute a self-supporting assembly in which the sheet serves to ensure the mechanical strength. Preferably, it is also used to fix the device in front of a support wall soundproofing. In addition, it protects the absorbent layer from external aggressions.

Furthermore, the device according to the invention is advantageously made of modular elements to be assembled on site in front of a support wall.

• la figure 1 est une vue en coupe d'un premier mode de réalisation de l'invention,
• la figure 2 est une vue en perspective de la tôle de l'élément absorbant de la figure 1,
• la figure 3 est une vue partielle en détail de la face extérieure de la tôle de la figure 2
• la figure 4 est une vue en coupe d'un autre mode de réalisation de l'invention
• la figure 5 est une vue du dessus de la couche de matériau absorbant de l'élément absorbant de la figure 4
• la figure 6 est la courbe du coefficient d'absorption acoustique d'un dispositif d'absorption ne comportant pas de couche de matériau absorbant en fonction de la fréquence
• les figures 7 et 8 sont les courbes du coefficient d'absorption acoustique en fonction de la fréquence pour deux dispositifs d'absorption conformes à l'invention
• la figure 9 est une vue en coupe illustrant la fixation du mode de réalisation de la figure 4 sur la paroi support
• la figure 10 est une vue en coupe illustrant la fixation du mode de réalisation de la figure 3 sur la paroi support
• et les figure 11 et 12 illustrent la fixation d'un autre mode de réalisation de l'invention sur la paroi support.

The invention will now be more fully described in the context of preferred features and their advantages, with reference to Figures 1 to 5 in which :

• the figure 1 is a sectional view of a first embodiment of the invention,
• the figure 2 is a perspective view of the sheet of the absorbent element of the figure 1 ,
• the figure 3 is a partial view in detail of the outer face of the sheet metal of the figure 2
• the figure 4 is a sectional view of another embodiment of the invention
• the figure 5 is a view from above of the layer of absorbent material of the absorbent element of the figure 4
• the figure 6 is the curve of the sound absorption coefficient of an absorption device having no layer of absorbent material as a function of frequency
• the Figures 7 and 8 are the curves of the acoustic absorption coefficient as a function of frequency for two absorption devices according to the invention
• the figure 9 is a sectional view illustrating the fixation of the embodiment of the figure 4 on the support wall
• the figure 10 is a sectional view illustrating the fixation of the embodiment of the figure 3 on the support wall
• and the figure 11 and 12 illustrate the attachment of another embodiment of the invention on the support wall.

The invention relates to an acoustic element operating by reflection and absorption of air vibrations or acoustic vibrations and for the acoustic correction of noisy premises or the soundproofing of boxes or enclosures containing noisy devices. This may include, for example, noisy industrial premises, such as wind tunnels, or public buildings such as hospitals. The invention also applies to boxes containing noisy machines.

The acoustic element according to the invention is intended to be placed on the inner walls of rooms or soundproof enclosures, or in the vicinity of these walls.

The absorbent element according to the invention essentially consists of a sheet 1 which has perforations and which is of embossed shape and a layer 2 of porous absorbent material, cellular or fibrous, which is fixed on the inner face 6 of the sheet 1.

The sheet 1 has a low rate of perforation, that is to say that the proportion of its surface that is occupied by holes or perforations is small relative to its total area. This rate is, for example, at most a quarter.

According to a particular embodiment as represented on the Figures 1 to 3 , the sheet 1 is rectangular in shape and its four edges 3 and 4 are folded 90 degrees towards the inner face 6 of the sheet 1 so as to form a rectangular housing in which the layer 2 of absorbent material is placed. The two opposite edges 4 of the sheet 1 are bent again 90 degrees so as to obtain flaps 5 parallel to the inner face of the sheet 1.

Advantageously, the height of the side walls 3 and 4 corresponds to the thickness of the absorbent layer 2 and the flaps 5 are made after the introduction of the layer 2 of absorbent material. They thus protect the edges of the absorbent layer, mainly from the mechanical point of view.

The sheet 1 is a metal sheet made for example of aluminum, steel or stainless steel. This sheet 1 is thin, preferably between 0.5 and 1.5 mm. The sheet is perforated, that is to say that it has small slots arranged in regular mesh. It is also embossed, that is to say it has bumps and hollows in a regular distribution repeated. In the case considered, it is deformed in such a way that the slots are pushed back, during its production, in a plane different from the initial plane of the sheet. II This is a perforated embossed sheet of the type of a metal plate deployed.

This is illustrated in particular on the figure 3 , which is a partial view on a large scale of the outer face 7 of the sheet 1. This figure shows two rows of slots 8 which have a first edge 9 which lies in the plane of the outer face 7 of the sheet and a deformed edge 11 which has been pushed over the outer face 7 during the production of the slots. It follows that there is a portion 12 of the sheet which is embossed, that is to say that it has been pushed out of the initial plane of the sheet, that is to say from the outer face 7, such that the slots have a certain height in the direction perpendicular to the plane of the sheet. It can be seen that the two rows of slots 8 are staggered with respect to one another, with a slight overlap of the slots of one row with respect to the slots of the neighboring row.

These slots are made by means of a saw blade-shaped tool that tears the metal and then folds it. The variable parameters are the shape of the tool which gives the length of the slot and the depth of penetration of the latter in the metal which gives the width of the mesh.

• format des mailles : 13 x 2 x 1 mm, à savoir longue diagonale (L sur la figure 3) = 13 mm, courte diagonale (C sur la figure 3) = 2 mm et hauteur de la fente = 1 mm,
• direction des longues diagonales de la maille : ± 3 mm, et
• direction des courtes diagonales de la maille : - 0/2 mm.

According to a particular example embodying the invention advantageously, the perforated embossed sheet obtained corresponds to the following dimensions:

• mesh size: 13 x 2 x 1 mm, ie long diagonal (L on the figure 3 ) = 13 mm, short diagonal (C on the figure 3 ) = 2 mm and height of the slot = 1 mm,
• direction of the long diagonals of the mesh: ± 3 mm, and
• direction of the short diagonals of the mesh: - 0/2 mm.

In the housing delimited by the edges 3 and 4 of the sheet ( figure 2 ) are engaged the edges of the layer 2 of porous absorbent material.

To form the porous absorbent layer, it is possible, for example, to use cellular organic materials such as melamine foam or polyurethane foam, or fibrous materials such as cotton, polyester, polypropylene, polychloroprene, etc. or mineral wools, for example glass wool or rockwool. The height of the edges 3 and 4 corresponds to the thickness of the absorbent layer and can be between 5 and 200 mm.

In the particular example described, the perforation ratio and the perforation density, that is to say the number of perforations per unit area of the sheet, have been optimized for acoustic absorption in the audible frequency range by the human being, in order to obtain a resistivity to the passage of air between 500 and 3300 N s / m ³ . However, these data are not limiting. They can vary in particular according to the applications of the invention.

When such a sheet is placed in front of a reflecting support, namely the wall of the enclosure to be soundproofed, the sheet functions as an absorbent material which has a selective character according to the reflection phenomena that occur between the support wall and the inner face 6 of the sheet 1.

$$\mathit{f}=2(\mathrm{C}/2\mathit{d})$$

$$\mathit{f}=3(\mathrm{C}/2\mathit{d})$$

etc.These reflections occur especially for frequencies, as a function of the incident pressure waves, whose values f are related to the thickness of the air gap existing between the sheet and the support wall, according to the following progression: $$\mathit{f}=\left(\mathrm{VS}/2\mathit{d}\right)$$

$$\mathit{f}=2(\mathrm{VS}/2\mathit{d})$$

$$\mathit{f}=3(\mathrm{VS}/2\mathit{d})$$

etc.

In these equations, C is the speed of sound in the air, for example 343 m / s at 20 ° C, and d is the thickness of the air space, that is the distance between the air gap. sheet and the support wall.

For the frequencies of the series, which correspond to a multiple of half the wavelength of the sound pressure, the values of the acoustic absorption coefficients take a minimum value and this results in significant valleys in the curve of absorption of the absorption device. To avoid the pitfalls of absorption curve, the layer of absorbent material 2 is associated with the sheet 1, this layer 2 being placed between the sheet 1 and the support wall, being applied to the sheet 1. In this way, the cavity resonances are damped by the absorbing material and the values of the absorption coefficients become homogeneous.

$$\mathit{f}=3(\mathrm{C}/4\mathit{d})$$

$$\mathit{f}=5(\mathrm{C}/4\mathit{d})$$

etc.A smoothing of the absorption curve is thus obtained, with maximum values of the absorption coefficient which are related to the thickness of the air space according to the following equations, which correspond to frequencies equal to an odd multiple of one quarter. of the wavelength: $$\mathit{f}=\left(\mathrm{VS}/4\mathit{d}\right)$$

$$\mathit{f}=3(\mathrm{VS}/4\mathit{d})$$

$$\mathit{f}=5(\mathrm{VS}/4\mathit{d})$$

etc.

By varying the thickness of the absorbent material layer and that of the air gap, the efficiency of the device can be varied over the frequency range so as to obtain an absorption curve as a function of the frequency. be as flat as possible for the range of frequencies to be filtered.

It is important that the method of fixing the layer of absorbent material on the sheet does not modify the structure of the perforated embossed sheet, that is to say that the absorbent material does not obstruct the slots 8, so that that the resistivity to the passage of air from the sheet is not changed.

Several methods for fixing the layer 2 of absorbent material on the inner face 6 of the sheet 1 can be provided. A first method is illustrated on the Figures 1 and 2 . The sheet is folded on at least two sides and the layer 2 is placed between the sheet and the folded edges. We can then, as shown on the figure 2 again fold the edges 90 degrees inwards, after the establishment of the layer 2, the flaps 5 blocking the layer 2 by plating on the inner face 6 of the sheet 1.

Another possibility is to fix the layer of absorbent material using a hot pressing process, a layer of absorbent material being strongly hot pressed on the sheet. During this operation, the absorbent material adheres to the asperities of the embossed sheet which constitute points of contact without sealing the perforations. The material here contains a binder which then ensures the fixing by gluing.

The fixing of the acoustic device thus produced on the support wall is carried out by means of fixing members which bear on the sheet metal 1, because this sheet generally benefits from mechanical strength characteristics related to its metallic nature which does not present the layer of porous material. The fixing members may advantageously be constituted by profiles connecting the sheet 1 to the support wall at the level of deformations of the sheet where it is removed from the layer of porous material, or by tie rods passing through all the layers of the acoustic device at level of the flaps 5 of the sheet which are formed overlapping the edges of the layer of porous material. The method of fixing such members in the support wall can be especially by screwing, possibly in pins previously installed when the nature of the support wall requires.

The figure 9 illustrates, in sectional view, such a method of attachment, showing how a void space is formed between the layer of porous material 2 and the support wall. It shows a tie rod 11, which passes through the sheet 1, the layer 2 of acoustic material, and the flap 5. The fastener is completed by a washer 12 and a hollow spacer 14 which is interposed on the tie rod 11 when this one is set up. It is then fixed in the support wall 15, for example by involving a pin 16. The washer 12 ensures the support of the flap 5 on the spacer 15, which maintains a distance relative to the wall 15 which corresponds to the desired thickness of the air space. The layer 2 is not subjected to any mechanical stress which could alter its acoustic qualities.

In the embodiment of the figure 4 where the layer 2 is fixed by bonding to the sheet 1, the free ends of the side walls 4 are advantageously folded 90 degrees outwardly to form lugs 10 which is fixed on the support wall. The height of the side walls 4 corresponds to the thickness of the air gap formed, that is to say to the distance provided between the sheet 1 and the support wall. This height corresponds to the thickness of the layer 2 increased by the thickness of free air provided between the layer 2 and the support wall.

The figure 10 illustrates, in sectional view, a method of fixing the device of the figure 4 . The outer flaps 10 of two adjacent devices are placed one over the other and traversed by a nail or similar member 17 which is fixed in the support wall 15 by pressing the flaps 10 on this wall, thus ensuring the desired thickness of the air space.

In both cases, a secure fixation is obtained which makes it possible to stiffen the absorbent device.

The figure 6 shows the curves of the sound absorption coefficient as a function of the frequency of the embossed perforated sheet placed in front of a wall for air gaps varying between 20 and 100 mm. It can be seen that, for all the curves, there are one or more significant depressions in the absorption curve, the frequency corresponding to these hollows being inversely proportional to the thickness of the air space.

The Figures 7 and 8 are corresponding curves for devices comprising a reflective sheet and an absorbent layer as provided by the invention. In the case of figure 7 the layer 2 of absorbent material is made of melamine foam and has a thickness of 60 mm. The space between the support wall and the porous layer 2 is minimal. The figure 8 is an example embodiment in which the layer 2 is also made of melamine foam and its thickness is 40 mm. The device according to the invention is disposed at 60 mm from the support wall, the thickness of the air space formed being therefore 100 mm.

It can be seen that on these two curves Figures 7 and 8 the hollows of the absorption characteristic are very damped and a very effective absorption curve is obtained. It can therefore be seen that the presence of the absorption layer 2 of absorbent material has a smoothing effect of the absorption curves and that by varying the thickness of this layer and the thickness of the air gap, that is to say the distance between the sheet 1 and the support wall, it is possible to obtain a very satisfactory absorption characteristic for a given frequency range.

The Figures 11 and 12 represent, still in section, a method of attachment of another embodiment of the device according to the invention.

In this case, the layer 20 of insulating material is fixed by gluing, by means of a glue layer or by hot compression, to a sheet 21 which projects from the layer 20 on the sides, in a straight line, so as to between two neighboring devices, advantageously in the form of identical slabs, a free space of acoustic material below the extensions 25 of the sheets 20.

A spacer 22 is associated with the assembly, to be fixed on the support wall 15. It carries on its free end a profile 23 ( figure 12 ), with current section shaped omega reversed, which is fixed on its central portion, for example by a rivet 24. This section 23 is housed with the end of the spacer 23 in the aforementioned free space, in a position where the extensions 25 of the plates 21 rest on lateral plates 26 of the profile 23. The extensions 25 of the sheets 20 are held on the profile 23 by means of a clip 27 which is clipped into the section 23 and which also constitutes a cover joint between the respective extensions of the plates of the two neighboring devices.

The device according to the invention can be used in particular in the building, for example for the production of absorbent dihedra for anechoic rooms, absorbent ceilings, or absorbent wall facings. The invention applies in particular in wind tunnels, industrial buildings, social-cultural buildings, the hospital sector.

The invention can also be used profitably in the industry to produce acoustic absorbent facings or silent devices, in particular in shipbuilding or aeronautics, the railway industry, the automobile industry, the acoustic enclosure of noisy machines, heating and air-conditioning equipment, agricultural and military equipment, as well as public works machinery, the computer industry and glass recycling containers.

It is apparent from the above description of embodiments of the invention that another purpose of the invention is that the perforated embossed sheet is used to ensure the mechanical strength of the sound absorption device by constituting a stiffening support for the acoustic wave absorption layer and realizing its protection.

It will also be understood that the elements according to the invention can be marketed by combining with the perforated embossed sheet and the acoustic absorption layer of the attachment to the support wall for which they are intended which ensure an air gap of predetermined thickness.

In practice, the layer of absorbent material is arranged fixed against the perforated embossed sheet, on the internal face thereof, by gluing on the asperities it has because it is embossed, and said layer is thus disposed between said sheet and the support wall for which it is intended, and at a distance from this support wall which is chosen in connection with the thickness of the layer of absorbent material to ensure a desired effect in correction of a sound spectrum in a range of determined frequency. It should be noted that in one of the preferred embodiments according to the invention, the perforated embossed sheet is itself shaped to impose a predetermined distance between the inner face of the absorbent layer and the support wall.

Finally, it emerges from all of the foregoing that the invention is not limited to the embodiments which have been specifically described in the course of the examples above and which, on the contrary, extends to all variant passing through equivalent means.

Claims (6)

1. Device for the soundproofing of premises or box-type structures, intended to be placed in front of a support wall defining the premises or box-type structure, comprising a metal element and a layer (2) of sound-absorbing material, characterised in that said metal element is a perforated embossed metal plate (1) that actively reflects acoustic waves and in that said layer (2) of porous sound-absorbing material is bonded onto said metal plate (1), so as to be placed, between the latter and the support wall, at a distance from said support wall which provides an air gap between said layer (2) of sound-absorbing material and said support wall, the thickness of said air gap being selected in conjunction with that of said layer (2) of sound-absorbing material so as to ensure a much sought-after effect in correcting a sound spectrum over a given range of frequency.
2. Device according to claim 1, characterised in that the layer (2) of sound-absorbing material is bonded to the metal plate (2) by hot compression, in the rough protuberances it presents on account of the metal plate involved being embossed.
3. Device according to any one of the previous claims, characterised in that said metal plate (1) is a plate of expanded metal.
4. Device according to claim 1, characterised in that it comprises fasteners for fixing said metal plate (1) into said support wall so that it is seated thereon, said fasteners including at least one set of tie rods (11) capable of passing in turn through the metal plate (1), the layer (2) of sound-absorbing material, and a flap (5) forming by folding the edges of said metal plate (1) and defining a housing capable of receiving the edges of said layer (2) of sound-absorbing material, and at least one spacer (14, 22) intended to be placed between said flap (5) and said support wall so as to bring about said air gap.
5. Device according to any one of the previous claims, characterised in that the perforation factor and the density of perforation of the metal plate (1) are determined in such a way that the resistance of said metal plate (1) to the passage of air is between 500 and 3,300 N s/m³.
6. Device according to any one of the previous claims, characterised in that the thickness of the layer (2) of porous sound-absorbing material is between 5 and 200 mm and/or in that the thickness of the metal plate (1) is between 0.5 and 1.5 mm.

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