Acoustic absorber/barrier composite

Abstract

A thermoformable acoustic sheet material that is lightweight and provides excellent sound attenuation over a wide range of frequencies includes a combination of sound attenuating materials, including an acoustic barrier having a relatively high density, a thermoformable sound absorbing layer having a relatively low density, a substantially air-impermeable layer between the barrier and the sound absorbing layer, and an acoustic performance enhancing scrim or perforated thermoplastic film on the opposite side of the sound absorbing layer. The combination is useful for preparing contoured acoustic treatments for reducing sound transmission from the engine compartment of a vehicle to the passenger compartment of the vehicle.

1 . A thermoformable acoustic sheet material comprising: 
 an acoustic barrier layer having an area weight of at least about 40 grams per square foot and a thickness of from about 1 to about 15 millimeters;    a sound absorbing layer having an area weight of from about 25 grams per square foot to about 100 grams per square foot and a thickness of at least about 15 millimeters;    a substantially impermeable layer having a thickness of from about 0.5 mils to about 80 mils disposed between the acoustic barrier layer and the sound absorbing layer; and    an acoustic performance enhancement layer having a thickness of from about 0.01 millimeters to about 4 millimeters, and an airflow resistance of at least about 500 Rayls, the sound absorbing layer being disposed between the airflow control layer and the acoustic performance enhancement layer.    
   
   
       2 . The thermoformable acoustic sheet material of  claim 1 , wherein the acoustic barrier layer is a fibrous mat.  
   
   
       3 . The thermoformable acoustic sheet material of  claim 1 , wherein the acoustic barrier layer is a mineral filled foamed plastic.  
   
   
       4 . The thermoformable acoustic sheet material of  claim 1 , wherein the acoustic barrier layer is a resin impregnated cotton shoddy material.  
   
   
       5 . The thermoformable acoustic sheet material of  claim 2 , wherein the acoustic barrier is a vertically-lapped fibrous mat.  
   
   
       6 . The thermoformable acoustic sheet material of  claim 1 , wherein the sound absorbing layer is a foamed thermoplastic material.  
   
   
       7 . The thermoformable acoustic sheet material of  claim 1 , wherein the sound absorbing layer is a vertically-lapped fibrous mat.  
   
   
       8 . The thermoformable acoustic sheet material of  claim 1 , wherein the substantially impermeable layer is a thermoplastic sheet.  
   
   
       9 . The thermoformable acoustic sheet material of  claim 1 , wherein the substantially impermeable layer is integral with the acoustic barrier layer.  
   
   
       10 . The thermoformable acoustic sheet material of  claim 1 , wherein the substantially impermeable layer is integral with the sound absorbing layer.  
   
   
       11 . The thermoformable acoustic sheet material of  claim 1 , further comprising a second substantially impermeable layer adjacent the other substantially impermeable layer, wherein one of the substantially impermeable layers is integral with the acoustic barrier layer, and the other substantially impermeable layer is integral with the acoustic barrier layer.  
   
   
       12 . The thermoformable acoustic sheet material of  claim 1 , wherein the substantially impermeable layer has an airflow resistance of at least 4000 Rayls.  
   
   
       13 . The thermoformable acoustic sheet material of  claim 1 , wherein the acoustic performance enhancement layer is a scrim fabric.  
   
   
       14 . The thermoformable acoustic sheet material of  claim 1 , wherein the acoustic performance enhancement layer is a perforated thermoplastic film.  
   
   
       15 . The thermoformable acoustic sheet material of  claim 1 , wherein the acoustic barrier layer is a fibrous mat comprised of a blend of synthetic fibers and natural fibers.  
   
   
       16 . The thermoformable acoustic sheet material of  claim 1 , wherein the acoustic barrier is a fibrous mat comprised of natural fibers, mineral fibers, or a combination of natural and mineral fibers that are impregnated or coated with a heat-fusible thermoplastic resin or a thermosettable resin.  
   
   
       17 . The thermoformable acoustic sheet material of  claim 1 , wherein the sound absorbing layer is a fibrous mat comprised of a blend of synthetic fibers and natural fibers.  
   
   
       18 . The thermoformable acoustic sheet material of  claim 1 , wherein the sound absorbing layer is a fibrous mat comprised of natural fibers, mineral fibers, or a combination of natural and mineral fibers that are impregnated or coated with a heat-fusible thermoplastic resin or a thermosettable resin.  
   
   
       19 . A motor vehicle having a passenger compartment separated from an engine compartment by a metal wall, and having a thermoformable acoustic sheet material disposed adjacent the metal wall, wherein the thermoformable acoustic sheet material comprises: 
 an acoustic barrier layer having an area weight of at least about 40 grams per square foot and a thickness of from about 1 to about 15 millimeters;    a sound absorbing layer having an area weight of from about 25 grams per square foot to about 100 grams per square foot and a thickness of at least about 15 millimeters;    a substantially impermeable layer having a thickness of from about 0.5 mil to about 80 mils disposed between the acoustic barrier layer and the sound absorbing layer; and    an acoustic performance enhancement layer having a thickness of from about 0.01 millimeters to about 4 millimeters, and an airflow resistance of at least about 500 Rayls, the sound absorbing layer being disposed between the airflow control layer and the acoustic performance enhancement layer.