WO2009007386A1

WO2009007386A1 - Method for producing an active acoustic panel and device for attenuating noises using such an active acoustic panel

Info

Publication number: WO2009007386A1
Application number: PCT/EP2008/058890
Authority: WO
Inventors: Nicolas Maisonnave; Octavio Hernandez Mascarell
Original assignee: European Aeronautic Defence And Space Compagny Eads France
Priority date: 2007-07-10
Filing date: 2008-07-09
Publication date: 2009-01-15
Also published as: FR2918780B1; FR2918780A1

Abstract

In order to produce a cladding panel (1) in a composite sandwich with a core that is cellular and acoustically active, the cellular core is prepared by producing hollow impressions and by incorporating acoustic transducers (40) into the said impressions. Notches in walls of the cells of the cellular core make it possible to produce cable ways (14) in which are routed the cables (41) supplying the transducers from an electric connection point (2) of the panel (1). An active noise control device, in particular for an aircraft, uses such panels as a replacement of the conventional cladding panels.

Description

Method for producing an active acoustic panel and noise attenuation device using such an active acoustic panel

The present invention belongs to the field of noise attenuation devices by the active control of dynamic transducers.

In particular, the invention is directed to a method for producing cladding panels incorporating means for vibrating a surface of the panel and relates to an active noise control device that can be modulated according to the configuration. a volume within which the noise must be controlled and implementing such dressing panels.

One-space noise reduction methods of measuring ambient noise and generating destructive noise by controlling the amplitude and phase of the destructive noise are known. Devices implementing these methods are most often referred to as active noise control systems.

To generate the destructive noise, the most general solution is to have in the space in which the noise must be reduced, for example the cabin of a vehicle, loudspeakers which are supplied with phases and intensities to generate acoustic waves that interfere with the level of sound energy in selected areas of the treated space. This solution of adding speakers is disadvantageous because of the weight, volume and installation constraints of the speakers Most often the space in which the speakers can be installed is limited and then poses problems of mechanical interference with other equipment and with cladding panels generally used for technical or aesthetic reasons.

In particular, when the noise reduction device is installed on an existing vehicle comprising passive covering panels designed without provision for the installation of an active noise control device, the mounting of the loudspeakers most often requires to modify and / or replace existing trim panels to install the active noise control device.

In addition, noise reduction systems generally use many loudspeakers that generate wiring and electrical constraints for their controls and power supplies, and also require the modification or replacement of existing trim panels. To avoid the drawbacks of known solutions, the invention proposes a method of producing a thin and light covering panel which incorporates dynamic excitation elements of the panel as well as the electrical wiring of said elements.

According to the method, a sandwich structure composite panel comprises a cellular core placed between a first skin, or inner skin, intended to be oriented towards a cabin and a second skin, or outer skin, on the face of the panel. facing opposite the face intended to be oriented towards the cabin. Before assembling the honeycomb core with the first and second skins the honeycomb core is subjected to at least two prior steps. a / a step of preparing the cellular core, said preparation step comprising the realization on one side of the honeycomb core to receive the first skin of at least one indentation, of depth less than the thickness e the alveolar core, adapted to receive a vibration generating transducer in the field of acoustic frequencies; b / a step of setting up at least one vibration generating transducer in the acoustic frequency range in each cavity.

In order to route the power supply son of the transducers without risk of damage in service of these son and without impact on the dimensional characteristics of the covering panel, during the step a preparation of the alveolar core notches are made in walls of the cells of the honeycomb core to create cable trays between the fingerprint (s) and an electrical connection point of the trim panel and to During step b, the transducer power cables are placed in the cable trays.

In order to make the intaglio (s) with the dimensional qualities required despite the instability of the alveolar core before it is secured to the skins, the alveolar core is fixed temporarily on a support by its face to receive the skin outer and a retaining plate having openings corresponding to the desired locations for fingerprints is provisionally fixed on the face of the alveolar core to receive the inner skin. The impressions are then machined in the alveolar core through the openings.

To ensure the quality of the dimensional stability of the cellular material during machining operations preferably an adhesive or non-slip element is placed between the support and the cellular material and or between the holding plate and the cellular material.

Alternatively, geometric shapes integral with the support and or the holding plate cooperate with the cells of the cellular material in order to maintain said cellular material during the machining operations.

Preferably, when the geometry of the panel is developable, to perform the machining operations with simple and inexpensive means such as machining machines 2 or 3 axes at least one face of the cellular core is kept flat during these machining operations.

Advantageously, in order to allow the manipulation of the cellular core in which the transducers and the supply cables are placed, in particular to carry out the inversion of the cellular core on the tooling for producing the panel, the transducers are fixed in the imprints with an adhesive at the moment of their placement in the imprint and the cables are self-maintained in the cable trays made with a width less than the diameter of the cables. The panel is advantageously made according to known production methods for the production of passive panels and does not require any significant modification of the methods and tools. So the inner skin is deposited on a tool having substantially the shape of the covering panel, the honeycomb core prepared according to the method is placed and shaped on said inner skin with its face comprising the transducers against said inner skin and the outer skin is placed on the face of the alveolar soul opposite to the face comprising the transducers.

For example, to obtain a panel in which the transducers are perfectly secured to the inner skin without adding glue, the inner skin and the outer skin are placed in the state of fabrics or fibers pre-impregnated with a thermosetting resin in a state not completely polymerized.

The invention also relates to a monolithic cladding panel as it can be obtained by the method of the invention. The panel comprises a cellular core placed between a first skin, called the inner skin, intended to be oriented towards a cabin and a second skin, called the outer skin, on the face of the cladding panel opposite the face intended to be oriented towards the cabin, said alveolar core and first and second skins being assembled to form the covering panel according to a so-called sandwich structure, and whose alveolar material comprises on its face in contact with the inner skin one or fingerprints in which there are transducers capable of generating vibrations in the acoustic frequency range, and said transducers being in contact on the one hand with the alveolar material of the core and on the other hand with the inner skin to vibrate said inner skin and said alveolar material of the soul.

Preferably the cables that feed the transducers are fed from the transducers to at least one electrical connection point of the panel in cable trays made recessed on one or both sides of the cellular material under the inner skin and or the outer skin.

Advantageously because of the relatively small thickness of the panels, each transducer is a flat component or an assembly of flat components, in particular made with a piezoelectric technology.

Advantageously for producing panels of small masses, the inner skin and or the outer skin are made of fiber impregnated with a polymerized resin and the cellular material is of the type of cells of random geometry foam type or cells of regular geometry for example hexagonal cells called honeycomb.

The invention also relates to a noise attenuation system in an at least partially enclosed space in which one or more such covering panels are electrically connected to a means for generating an electrical signal for supplying the transducers so that said panel generates an acoustic wave whose phase and amplitude are destructive of ambient noise in at least part of the space. An aircraft is advantageously made quieter at the cabin or cockpit by means of such a noise attenuation system and this without significant penalty on the mass and the volume occupied by the trim panels

The detailed description of an exemplary embodiment of the invention is made with reference to the figures which show schematically: Figure la: a view of a sandwich structure panel; Figure Ib: a partial section of a panel at a transducer; Figure Ic: a view of a complete panel incorporating several transducers; Figure Id: a schematic representation of an active noise control device in an aircraft cabin;

Figures 2a to 2f: sections and perspective views illustrating different steps of the process for preparing the cellular material;

Figure 3: an example of a holding plate and openings; 4a and 4b: an example of a method of assembly of the cellular core and the skins of the panel.

A cladding panel 1 according to the invention is of the type of a sandwich composite panel comprising a core 10 of foam material of thickness e, for example comprising hexagonal cells called nest bee, between two skins adhered to the cellular material, a skin 20 on the face of the panel located on the side of a space 81 of a cabin to be treated on the acoustic plane, called the inner skin, and a skin 30 on the face located on the opposite side of the cabin, said outer skin. Panel 1 is flat or curved with single curvature or double curvature.

In the embodiment described the panel is substantially constant thickness E, but the proposed solution is applicable to panels whose thickness is not constant.

Such covering panels have the advantage of being both relatively resistant and light, which explains why they are widely used in transport and especially in aircraft.

The covering panel of Figures 1a and 1b illustrates the arrangement of the layers forming the panel of composite material. Typically a panel of this technology for an aircraft cabin trim has a total thickness E of between 5 and 10 mm.

In order to make the panel acoustically active, at least one transducer 40, advantageously a piezoelectric type transducer which can be produced with a small thickness, whose thickness is less than the thickness e of the cellular material 10, is to say less than the height of the cells when the material is a honeycomb cell material as illustrated in the examples of the figures, is placed inside the panel 1, with one side of said transducer in contact with the inner skin 20 of the panel 1.

To obtain this result, an indentation recess 11 having substantially the dimensions of the transducer 40 is arranged in the cellular material 10, on a face 12 corresponding to the face of the side of the inner skin 20, and said transducer is maintained in said cavity.

The transducer 40 also includes 41 electrical conductor cables that provide power. Preferably, these cables 41 pass through the cellular material 10 before or after being conveyed from the transducer 40 to a point 2 of electrical connection of the active panel 1 placed preferably on the face situated on the side of the outer skin 30 of said panel. Advantageously notches 14 in the walls of the cells of the material alveolar 10 form a cable tray 14 in which the cables 41 are routed to a point corresponding to the electrical connection point 2 of the trim panel 1. Advantageously the notches are made with a width less than the diameter of the cables which are, because of elasticity of the walls of the cellular material, self-held in position during the subsequent operations of producing the panel, in particular the draping operations of the skins which are then able to undergo a single thermal cure of polymerization.

Preferably, the notches are made with the minimum depth so that the cables are flush with the surface 12 or 13 of the cellular material inside or outside so as not to affect the structural strength of the cellular core, but sufficient for the cables to exceed not of said surface so that the presence of the cables 41 does not create on the faces of the panel 1 any significant deformation of the inner or outer skin 30. In order to maintain a sufficient rigidity of the panel 1 in the zone comprising a transducer 10, preferably the transducer is made or chosen with a thickness less than the thickness e of the cellular material 10.

Depending on its dimensions and the sound power to be radiated, the number of transducers 10 in the panel 1 is variable and preferably all the transducer power cables are routed to the same electrical connection point 2 of the panel 1 or to a limited number of connection points.

The realization of such a panel industrially poses many constraints. Among these constraints it is necessary to consider the compatibility of the process with the known methods used and qualified for the production of cladding panels, the reproducibility of the results and an acceptable manufacturing cost.

When the cladding panels must be made in two versions, a passive panel version and an active panel version, it is also advantageous that the same tools can be used. This is especially true for expensive tools to make or maintain as for example large molds.

In addition, the active panel 1 produced must not present an unacceptable mass penalty nor lose the characteristics, in particular resistance, of the passive panel that it could replace. The description of an embodiment of a method according to the invention for producing an active cladding panel 1 according to the panel described above is made with the example of a curved panel with a simple curvature in a technology used in aircraft cabin linings. Before making the panel 1, the cellular material 10 is prepared. In a first step, FIG. 2a, the honeycomb material 10, previously cut to the dimensions of the covering panel 1 or of a blank of the covering panel, is positioned on a support 60 of stable dimensions and shape, the face 13 of the cellular material on the outer side of the panel 1 against said support. Advantageously, when the shape of the panel is developable, the support 60 is planar to facilitate the preparation operations of the cellular material to be incorporated in the panel 1, and in particular the machining of the cellular material with machines with two or three axes of displacement or manual machines. When the geometry of the panel does not make it possible to use a plane support 60, for example when the panel has double-curved shapes, the support 60 is made with a geometry in agreement with the geometry of the panel to be produced and means for More complex but conventional machining featuring machining heads with a higher number of axes are used. In addition to its rigidity sufficient to maintain its shape, the support 60, which may consist for example of a bottom plate or any tooling for obtaining the geometry required for the panel, ensures the lateral stability of the cellular material 10. In fact the cellular materials when not yet secured with skins are known to be very easily deformable. The lateral stability of the cellular material 10 on the support is obtained for example by depositing on the support 60 an adhesive coating 61, for example an adhesive tape on both sides, or non-slip which makes it possible to temporarily hold the cellular material 10 by the edge of the cells to the support 60 or for example by means of elements reliefs (not shown), as bosses on the support 60, which are arranged to cooperate with the cells of the cellular material 10 and prohibit the movements of said cellular material in parallel directions to the surface of the support 60. When an adhesive 61 is implemented, it is essential that it can be easily removed from the wall of the cells so as not to modify the adhesion characteristics of the skin 20 which will later come into contact with the cellular material or at least that this adhesive is without negative influence on said adhesion characteristics. In a second step, FIG. 2b, a retaining plate 62, referred to as an upper plate, is placed on the free face 12 of the cellular material 10, that is to say the face 12 opposite to the face 13 in contact with the support 60 and which is intended to be on the side of the inner face of the covering panel 1, and said upper plate comprises, as in the case of the support 60 means 63 (adhesive, non-slip, bosses ...) to ensure the lateral stability of the material alveolar 10 on the face 12 considered.

The cellular material placed between the support 60 and the upper plate 62 is thus perfectly stiffened, which a peripheral densification of the panel, for example by means of a resin, does not make it possible to obtain satisfactorily on panels of large dimensions and / or thin and / or low density and without the need to secure the cellular material 10 with one of the skins (30) of the panel which generally assumes a first thermal cure of polymerization, that the cellular material 10 is shaped and which limits the possibilities of intervening on the face 13 considered alveolar material.

The upper plate 62 further comprises, as illustrated in FIG. 3, openings 64 whose locations and shapes are a function of the locations and shapes of the transducers 40 to be incorporated in the covering panel 1. By location of the openings 64, it is It should be understood that said openings are placed relative to the cellular material 10 positioned on the support 60 such that they correspond to the desired locations of the transducers in the cellular material 10 after its integration in the panel 1 taking into account the dimensional variations during the curvature of the cellular material.

By the shape of the openings 64, it should be understood in the broad sense that the openings have geometric shapes and dimensions adapted to the realization of step three of the method described below and that these geometric shapes and these dimensions are not only dependent on transducers 40 used but also means and methods implemented to achieve the next step three. In a third step, FIG. 2e, indentations 11 are machined by the openings 64 in the cellular material 10 in the form of the transducers 40 including with regard to the depth of the indentations 11 which corresponds to the thickness of the said transducers. . The impressions 11 are machined automatically, for example by means of a numerically controlled machine, or by means of a manual or semi-automatic machine (not shown). In these latter cases, the openings 64 of the upper plate 62 are advantageously designed to serve as a machining jig or to position and maintain such a jig. The machining means are known means, for example a milling cutter 65, and the maintenance of the cellular material 10 by the support 60 and the upper plate 62 guarantees the quality of the impressions thus made both for their dimensions and for their locations.

In a fourth step, Figure 2d, the upper plate 62 is removed and notches 14 are formed in the walls of the cells to create a cable path 14 to allow the routing of the electrical cables 41 for supplying the transducers 40 between each location a transducer and at least one connection point 2 of the active panel 1. These notches are made by any method for cutting the material to a width less than the diameter of the cables such as for example by means of a blade or a strawberry 66.

In an alternative embodiment of this fourth step, the cellular material 10 is separated from the support 60 and then notches are made in the walls of the cells on the face 13 of the cellular material on the outer side of the covering panel 1 to form cable trays provided on said face.

In practice, the various proposed embodiments of step four of the method can be implemented for the same panel insofar as the electrical cables 41 for supplying the transducers 40 are likely to be routed, following more or less complex paths, towards the location of the connection point 2 for some on one side of the honeycomb material and for others on the other side and or some cables 41 that can be routed for part of their journey on one side and for another part on the other side of the cellular material.

In a fifth step, FIG. 2e, a transducer 40 to which its supply cables 41 have been connected is placed in each cavity 11 made for this purpose in the cellular material 10 and the power cables 41 are positioned in the cable trays. 14 to be routed to the connection point 2 of the panel 1 before or after passing through the honeycomb material as appropriate.

In order to keep the transducers 40 in the cavities 11 for the purpose of the subsequent manipulations, each transducer 40 is fixed to the cellular material 10 by means of at least one point of glue 42. The glue is chosen to be compatible with the considered materials, for example a silicone adhesive.

In order to keep the power cables 41 of the transducers in the cable trays, in particular on the part of the cable trays situated on the same face 12 of the cellular material 10 as that where the transducers 40 are fixed, the said cables are self -maintenus by the mechanical stress generated by the fact that the width of the notches made is less than the diameter of the cables.

In a sixth step, the cladding panel is prepared in a conventional manner, that is to say by implementing a method similar to that used for producing a passive cladding panel but in which the honeycomb material is replaced. by the foam material prepared according to steps one through five of the method as just described. For example, as illustrated in FIGS. 4a and 4b, plies of a fabric pre-impregnated with an uncured thermosetting resin and intended to constitute the inner skin 20 of the panel 1 corresponding to the inner face of said panel are placed on a tool 50 of which the shape substantially represents the shape of the panel on the side of the cabin.

In this case the working temperature is adapted to the characteristics of the impregnating resin to avoid having too much adhesion of the resin during the introduction of the cellular material.

The cellular material 10, separated from the support 60 and the upper plate 62 used for the operations of preparation of said cellular material and comprising the transducers 40 and the cables 41, is placed on the folds of fabric to form the inner skin 20 of which it marries the curvatures, with its face 12 on the side of which are placed the transducers 40 in contact with said folds of fabric. Due to the maintenance of the transducers 40 by glue 42 and wires

41 in the notches, as specified in step five, the cellular material 10 is returned to the folds of fabric placed on the tool 50 without risk of displacement of the transducers and son.

Folds of a fabric pre-impregnated with a thermosetting unpolymerized resin to form the outer skin 30 of the panel 1 are placed on top of the cellular material 10 on the face 13 opposite the side placed on the tooling side 50, taking care to make through said folds by the power cables 41 of the transducers, a priori near the point 2 chosen as the electrical connection point of the active panel. Other means depending on the technology used to make the panel 1 are put in place if necessary. Thus, as shown in FIG. 4b, it is possible to put in place, for example, drainage fabrics 53, 54 intended to absorb the excess resin contained in the prepreg, wedges 55 to prevent sagging of the panel on the sides, one against -form 51, a bladder 57 to apply pressure by practicing a partial vacuum ...

The panel thus prepared in a conventional manner is then placed in an oven and undergoes a heat treatment and pressurization of polymerizing the resin of the fabrics to form the inner and outer skins 30 of the panel. When a counter-form 51 is used on the outer face of the panel, said counter-form has an opening 52 for the passage of the electric cables 41 during the polymerization phase. The said opening 52 is sealed after the passage of the cables 41 and before the pressurization to avoid local depression on the skin which would lead to local deformation.

During this polymerization phase, the transducers 40 are secured to the inner skin 20 of the panel 1 by the resin of the skin material in the same manner as the cellular material and said transducers are able to transmit the vibrations to said skin interior to generate acoustic waves.

The panel 1, once cured, is removed from the tooling 50 and the associated tooling elements and undergoes finishing operations, in particular the mounting of the electrical connectors which are associated with the transducer supply cables.

Thus, the method makes it possible to produce, industrially, a covering panel 1 made of composite material comprising integrated active acoustic treatment means without calling into question the processes for producing similar passive panels, in particular in a single thermal polymerization cure.

In addition, the method makes it possible to produce geometrically identical active panels, to the electrical connection means associated with the connection point 2 near, to existing passive panels and, when the panel is made, the number and the arrangement of the transducers 40 are easily adaptable to the specific configuration for a specific use.

In this case, on the one hand, the active panels can be made, at least in part, with tools or tooling parts used to produce the passive panels and, on the other hand, the passive and active geometrically identical panels are advantageously interchangeable to allow rapid adaptation of an active noise control system according to the changes, in particular the arrangements, the space 81 of the cabin to be treated acoustically.

To produce an active noise control system in a particular zone, the panels 1 according to the invention are for example manufactured according to the shapes of the volume of the space 81, such as that of a cab of a vehicle in general. and a cabin of an aircraft 8 in particular, to be covered with cladding panels for reasons of thermal comfort, visual and acoustic in particular. In Figure Id only a fuselage element of an aircraft 8 is shown to illustrate the space 81 corresponding to all or part of a cabin for passengers. Such a space may also correspond to the volume of a cockpit or that of a rest area for the crew.

A means 7 is electrically connected to the panels comprising transducers 40 in order to supply the said transducers so that the panels, by means of the said transducers, produce acoustic waves of amplitudes and controlled phases so that the said waves acoustics are destructive of noises in desired areas of space 81.

The means 7 comprises in known manner, for example, devices, such as microphones for measuring the noises in the space 81, amplifiers for producing the electrical signals for supplying the transducers and means, for example a calculator, for processing the measurement signals and drive the amplifiers.

Claims

A method of manufacturing a trim panel (1) of a cabin made of a composite material, in which a cellular core (10) is placed between a first skin (20), called an inner skin, intended to be oriented towards the cabin and a second skin (30), called the outer skin, on the face of the cladding panel opposite to the face intended to be oriented towards the cabin, the said alveolar core and first and second skins being assembled to constitute the panel of d cladding according to a so-called sandwich structure, characterized in that it comprises, before assembling the alveolar core (10) with the first and second skins (20, 30), the steps of: a / preparation of the alveolar core (10), said preparation step comprising the realization on one face (12) of the honeycomb core (10) to receive the first skin (20) of at least one indentation (11), of depth less than the thickness e of the alveolar soul, able to receive a vibration generating transducer in the acoustic frequency range; b / establishment of at least one transducer (40) for generating vibrations in the acoustic frequency range in each cavity.

2. The method according to claim 1, wherein step a of preparing the cellular core also comprises making notches in the walls of the cells of the cellular core (10) to create one or more cable trays (14). ) between the at least one indentation (11) and an electrical connection point (2) of the cladding panel (1) and wherein the step b comprises the placement of electrical supply cables (41) of the transducers (40). ) in cable trays; The process of claim 1 or claim 2 wherein the step of preparing the cellular core comprises the steps of:

- provisionally fix the alveolar core (10) on a support (60) by a face (13) of the cellular core (10) to receive the outer skin (30);

- provisionally fix on the face (12) of the cellular core (10) to receive the inner skin (20) a holding plate (62) having at least one opening (64) corresponding to a desired location of a footprint ( 11); - Machining the fingerprint (s) (11) in the alveolar core (10) by the opening or openings (64). - Method according to claim 3 wherein the holding plate (62) has one or more openings corresponding to the cable paths (14) by which the notches in the cell walls of the honeycomb core (10) are machined to achieve the cable trays (14). - The method of claim 3 wherein the holding plate (62) and or the support (60) are separated from the honeycomb core (10) for machining the notches of the cell walls of the honeycomb core (10) constitute the cable trays (14). Method according to one of Claims 3 to 5, in which an adhesive or non-slip element (61, 63) is placed between the support (60) and the honeycomb material (10) and or between the holding plate (62) and the cellular material (10) for maintaining said cellular material during the machining operations of step a. - Method according to one of claims 3 to 6 wherein geometric shapes secured to the support (60) and or the holding plate (62) cooperate with the cells of the honeycomb material (10) to maintain said cellular material during the machining operations of step a. - Method according to one of the preceding claims wherein at least one face (12, 13) of the cellular core (10) is held flat during step a. - Method according to one of the preceding claims wherein the at least one transducer (40) is fixed in the cavity (11) with an adhesive (42) in step b. 0- A method according to one of claims 2 to 9 wherein the cables (41) are self-maintained in the cable tray (s) (14), under the effect of mechanical stresses generated by the honeycomb core material (10), during the operations of making the trim panel. A method in which the inner skin (20) is deposited on a tool (50) having substantially the shape of the trim panel (1), wherein the honeycomb core (10) prepared according to one of the preceding claims. is placed and shaped on said inner skin with the face (12) having the transducer (s) (40) against said inner skin and wherein the outer skin (30) is placed on the face (13) of the alveolar core opposed to the face (12) comprising the transducers (40). 2- The method of claim 11 wherein the inner skin (20) and or the outer skin (30) are placed in the state of fabrics or fibers pre-impregnated with a thermosetting resin in a not fully polymerized state. 3- covering panel (1) of a cabin having a honeycomb core (10) placed between a first skin (20), said inner skin, intended to be oriented towards the cabin and a second skin (30), said skin outside, on the face of the facing panel opposite the face intended to be oriented towards the cabin, said alveolar core and first and second skins being assembled to form the covering panel according to a so-called sandwich structure, characterized in that the cellular material comprises on one face (12) in contact with the inner skin (20) at least one cavity (11) in which there is a transducer (40) capable of generating vibrations in the acoustic frequency range, said transducer being in contact on the one hand with the cellular material of the core (10) and on the other hand with the inner skin (20).

14- covering panel according to claim 13 wherein the transducer or transducers (40) are fed by cables (41) conveyed from the transducers to at least one electrical connection point (2) of the panel (1) in paths of cables (14) made recessed on one or both sides (12, 13) of the foam material (10) under the inner skin (20) and or the outer skin (30).

The cladding panel of claim 13 or claim 14 wherein the transducer (40) is a component or assembly of flat components.

16- covering panel according to one of claims 13, 14 or 15 wherein the transducer (40) is a component or an assembly of flat components piezoelectric type.

17- covering panel according to one of claims 13 to 16 wherein the inner skin (20) and or the outer skin (30) is made of fiber impregnated with a polymerized resin.

18- dressing panel according to one of claims 13 to 17 wherein the foam material (10) is a foam-type random geometry cell material. 19- dressing panel according to one of claims 13 to 17 wherein the cellular material (10) is a cell material of regular geometry repetitive.

20- dressing panel according to claim 18 wherein the honeycomb material (10) is a honeycomb hexagonal cell material.

21- noise attenuation system in a space (81) at least partially enclosed in which at least one covering panel (1) according to one of claims 13 to 20, said active panel, is electrically connected to a generator (7) of an electrical signal supplying the transducers (40), said electrical signal being determined so that said active panel produces an acoustic wave whose phase and amplitude are destructive of an ambient noise in at least one part of the space (81).

22- Aircraft (8) comprising at least one space of a cabin (81) whose acoustic environment is controlled, at least locally, by a system according to claim 21.