Sound-absorbing panel and method of making

Abstract

A sound-absorbing panel is constructed, having first and second or inner and outer surfaces, with indentations in each surface that connect to each other via zones of communication. The indentations in the outer surface are divergent and generally circular in cross-section taken parallel to the outer surface. The indentations in the inner surface may be similar to the indentations on the outer surface, but preferably will comprise a series of parallel grooves. The indentations in the outer surface are constructed by simultaneously drilling a plurality of holes, preferably of frusto-conical configuration.

What is claimed:  
     
         1 . The method of making a sound-absorbing panel comprising the steps of: 
 (a) providing a sheet of panel material having first and second generally parallel spaced-apart surfaces;    (b) making first indentations in the first surface; and    (c) making second indentations of generally circular cross-section in the second surface of the panel and of a depth to communicate with first indentations in the first surface at zones of communication, and with the second indentations being divergent from the zones of communication to the second surface; and    (d) wherein the step of making second indentations comprises the step of simultaneously drilling a plurality of holes in said second surface to form the second indentations.    
     
     
         2 . The method of  claim 1 , wherein the step of simultaneously drilling comprises providing a gang of rotating drill bits mounted on a fixture for simultaneous movement toward and away from said second surface, and moving the fixture toward and away from the second surface while the drill bits are rotating, to drill the plurality of holes in the second surface.  
     
     
         3 . The method of any one of claims  1 - 2 , wherein the drilling step comprises drilling a plurality of frusto-conical holes.  
     
     
         4 . The method of any one of claims  1 - 2 , wherein the step of making first indentations comprises simultaneously cutting a plurality of generally parallel grooves in said first surface.  
     
     
         5 . The method of  claim 4 , wherein the cutting step comprises cutting grooves that are convergent from the first surface to the zones of communication.  
     
     
         6 . The method of claim any one of claims  1 - 2 , including the step of applying a layer of sound-absorbing material to said second surface.  
     
     
         7 . The method of  claim 6 , including the step of applying a layer of support material to said layer of sound-absorbing material, to sandwich the later of sound-absorbing material between the second surface and the layer of support material.  
     
     
         8 . An acoustic panel made according to the method of any one of claims  1 - 2 , comprising a sheet of panel material having first and second generally parallel spaced-apart surfaces defining therebetween the panel, with a plurality of first indentations in the first surface adapted to receive soundwaves; with a plurality of second indentations in the second surface; with a least some of the second indentations in the second surface having zones of communication with first indentations in the first surface to define through-holes through the panel; and with the second indentations being generally circular in transverse cross-section parallel to the second surface and being divergent from the zones of communication with the first indentations to the second surface; whereby soundwaves entering the first indentations pass through the zones of communication and diverge as they pass through the second indentations.  
     
     
         9 . The panel of  claim 8 , wherein the second indentations are generally frusto-conical in configuration.  
     
     
         10 . The panel of  claim 9 , wherein the second indentations have included angles in cross-section that are within the range of 15°-30°.  
     
     
         11 . The panel of  claim 10 , wherein the included angle is within the range of 25°-30°.  
     
     
         12 . The panel of any one of claims  8 , wherein the first indentations are convergent from the first surface to the zones of communication with the second indentations.  
     
     
         13 . The panel of  claim 12 , wherein the zones of communication are approximately 1 mm 2  in transverse cross-section.  
     
     
         14 . The panel of  claim 12 , wherein the first indentations comprise a plurality of generally parallel grooves.  
     
     
         15 . The panel of  claim 14 , wherein the grooves are of generally inverted V-shaped cross-section.  
     
     
         16 . The panel of  claim 15 , wherein the groove centers are spaced apart approximately 5 mm.  
     
     
         17 . The panel of  claim 14 , wherein the grooves are of generally inverted funnel-shaped cross-section.  
     
     
         18 . The panel of  claim 14 , wherein the grooves are of generally dome-shaped cross-section.  
     
     
         19 . The panel of any one of  claim 8 , wherein the panel includes a layer of sound-absorbing material proximate the second surface, for absorbing sound as sound waves diverge through the second indentations.  
     
     
         20 . The panel of  claim 19 , wherein the panel includes a layer of support material against the layer of sound-absorbing material, sandwiching the layer of sound-absorbing material between the second surface and the layer of support material.  
     
     
         21 . An acoustic panel comprising a sheet of panel material having first and second generally parallel spaced-apart surfaces defining there between a panel; with a plurality of first indentations in the first surface adapted to receive soundwaves; with a plurality of second indentations in the second surface adapted to diverge soundwaves; with at least some of the second indentations in the second surface having zones of communication with first indentations in the first surface to define through-holes through the panel; and with the first indentations and the second indentations each comprising generally parallel spaced-apart grooves in their respective surfaces, with the grooves of the first and second indentations intersecting at acute angles to form the zones of communication; whereby soundwaves entering the first indentations pass through the zones of communication and diverge as they pass through the second indentations.  
     
     
         22 . The panel of  claim 21 , wherein said acute angles are within the range of 30° to 60°.  
     
     
         23 . The panel of  claim 2 , wherein the acute angles are approximately 45°.