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A process for the production of a panel ( 9 ) with a fitted acoustically resistive layer, including at least one central core with porous structure bounded on one side by a structural layer covered with a porous acoustically resistive layer and, on the other side, by a total acoustical reflector, in

A process for the production of a panel ( 9 ) with a fitted acoustically resistive layer, including at least one central core with porous structure bounded on one side by a structural layer covered with a porous acoustically resistive layer and, on the other side, by a total acoustical reflector, in which, successively, acoustically resistive strips are laid down to form the layer on a mold (M) shaped like the panel to be obtained, the structural layer is emplaced, the core of porous structure is emplaced, the total reflector is emplaced, then the mold (M) is withdrawn from the panel. When laying down on the mold (M) the acoustically resistive layer, the porosity of this latter is locally adapted to correspond with the characteristics of the sonic wave at the point of impact, the correlation between characteristics and impact region being previously determined by conventional acoustical techniques applied to a test panel identical to that to be produced.

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1. Process for the production of a panel with a fitted acoustically resistive layer comprising at least one central core of porous structure bounded on a first side with a structural layer, the structural layer covered with a porous acoustically resistive layer and, bounded on a second side with a t

1. Process for the production of a panel with a fitted acoustically resistive layer comprising at least one central core of porous structure bounded on a first side with a structural layer, the structural layer covered with a porous acoustically resistive layer and, bounded on a second side with a total acoustical reflector, comprising the successive steps of:laying down said acoustically resistive layer in strips on a mold according to a profile of the panel to be obtained;placing said structural layer on said resistive layer;placing said core with a porous structure on said structural layer;placing said total reflector on said core; andwithdrawing the mold from the thus-formed panel, wherein,there is first produced a continuous strip of acoustically resistive material constituted by end to end sections of different porosities and said strip is laid down on the mold to form said acoustically resistive layer, andthe porosity and length of each section as well as a method of laying down each section is predetermined such that once the acoustically resistive layer is laid down, the acoustically resistive layer will be divided into at least as many contiguous regions as the different porosities in said strip, in correspondence with different acoustical zones detected during a preliminary correlation carried out with help of conventional acoustic techniques on a test panel identical to that to be produced. 2. Process according to claim 1, wherein the acoustically resistive material is selected from the group comprising cloth or metallic meshes and cloth of carbon fibers or glass fibers pre-impregnated with a thermoplastic or thermosetting resin. 3. Process according to claim 1, wherein before withdrawing to mold, the panel is subjected to consolidation by heating the thus-formed panel. 4. Process according to claim 1, wherein the acoustically resistive material is selected from the group of cloths or metallic meshes and the various porosities are obtained by modifying, during weaving, the spacing between the weft or warp filaments. 5. Process according to claim 1, wherein the acoustically resistive material is selected from the group of carbon fiber cloth or pre-impregnated glass fiber cloth, and the various porosities are obtained by varying a diameter and/or the distribution of holes pierced in said material. 6. Panel with an acoustically damping layer, obtained according to the process of claim 1. 7. Process for the production of a panel with a fitted acoustically resistive layer comprising at least one central core of porous structure bounded on a first side with a structural layer which structural layer is covered with a porous acoustically resistive layer and, bounded on a second side with a total acoustical reflector, comprising the successive steps of:laying down said acoustically resistive layer in strips on a mold according to a profile of the panel to be obtained;placing said structural layer on said resistive layer;placing said core with a porous structure on said structural layer;placing said total reflector on said core; andwithdrawing the mold from the thus-formed panel, wherein,there is first produced a plurality of strips of acoustically resistive material of different porosities, and there is laid down on the mold successively said strips in an order and with deposition techniques predetermined such that once the acoustically resistive layer is laid down, the acoustically resistive layer will be divided into at least as many contiguous regions as there are different porosities, in correspondence with different acoustic regions detected during a preliminary correlation carried out with help of conventional acoustic techniques on a test panel identical to that to be produced. 8. Process according to claim 7, wherein the acoustically resistive material is selected from the group comprising cloth or metallic meshes and cloth of carbon fibers or glass fibers pre-impregnated with a thermoplastic or thermosetting resin . 9. Process according to claim 7, wherein before withdrawing to mold, the panel is subjected to consolidation by heating the thus-formed panel. 10. Process according to claim 7, wherein the acoustically resistive material is selected from the group of cloths or metallic meshes and the various porosities are obtained by modifying, during weaving, the spacing between the weft or warp filaments. 11. Process according to claim 7, wherein the acoustically resistive material is selected from the group of carbon fiber cloth or pre-impregnated glass fiber cloth, and the various porosities are obtained by varying a diameter and/or the distribution of holes pierced in said material. 12. Panel with an acoustically damping layer, obtained according to the process of claim 7. 13. Process for the production of a panel with a fitted acoustically resistive layer comprising at least one central core of porous structure bounded on a first side with a structural layer which structural layer is covered with a porous acoustically resistive layer and, bounded on a second side with a total acoustical reflector, comprising the successive steps of:laying down said acoustically resistive layer in strips on a mold according to a profile of the panel to be obtained;placing said structural layer on said resistive layer;placing said core with a porous structure on said structural layer;placing said total reflector on said core; andwithdrawing the mold from the thus-formed panel, wherein,there is first produced a strip of an acoustically resistive material of a same nature but with porosity varying longitudinally of the strip and said strip is laid down on the mold, andthe method of varying the porosity and of laying down the strip being predetermined such that once the acoustically resistive layer is laid down, the acoustically resistive layer has local variations of porosity corresponding to different acoustic regions detected during a preliminary correlation carried out with help of conventional acoustic techniques on a test panel identical to that to be produced. 14. Process according to claim 13, wherein the porosity of strip varies according to different levels. 15. Process according to claim 14, wherein at each of the levels the transition of the porosity is progressive. 16. Process according to claim 13, wherein the acoustically resistive material is selected from the group comprising cloth or metallic meshes and cloth of carbon fibers or glass fibers pre-impregnated with a thermoplastic or thermosetting resin. 17. Process according to claim 13, wherein before withdrawing to mold, the panel is subjected to consolidation by heating the thus-formed panel. 18. Process according to claim 13, wherein the acoustically resistive material is selected from the group of cloths or metallic meshes and the various porosities are obtained by modifying, during weaving, the spacing between the weft or warp filaments. 19. Process according to claim 13, wherein the acoustically resistive material is selected from the group of carbon fiber cloth or pre-impregnated glass fiber cloth, and the various porosities are obtained by varying a diameter and/or the distribution of holes pierced in said material. 20. Panel with an acoustically damping layer, obtained according to the process of claim 13.