Abstract:
A tunable sound absorber including a fibrous batt having a plurality of fibers and a film coupled to the surface of the fibrous batt, where the fibers penetrate the film to create perforations, and where the perforations transfer sound energy to the fibrous batt and the sound energy is absorbed by the fibrous batt.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to sound absorption material. More specifically, the present invention relates to a fibrous acoustical absorber used in automotive trim panels that may be tuned during its fabrication for maximum sound absorption over a wide frequency range or in a specific frequency range. 
     A sound absorbing material must have the proper combination of hardness, density, and air flow to absorb and attenuate sound in a desired manner. Sound energy is comprised of high and low waves of air pressure that propagate through the air and can be absorbed and attenuated through many actions or mechanisms. Many materials absorb and attenuate sound through viscous losses (i.e., the movement or shearing of air in a material) or by sound induced mechanical/kinetic energy losses in the fibers of a material that result in sound energy being converted to heat. Generally, a foam-like material will attenuate sound though viscous losses and a fibrous material will attenuate sound through the kinetic energy dissipation created by the movement of its fibers. Other materials may utilize a combination of both viscous and mechanical losses. 
     The porosity and stiffness of a material will affect its air flow characteristics and thus its sound absorption and attenuation characteristics. For example, a relatively stiff and nonporous material having high acoustical resistance, such as brick, will merely reflect sound, as the sound energy will not easily propagate through the brick. Conversely, a window screen with low acoustical resistance will allow large amounts of air and thus sound to quickly propagate through it, attenuating only a small amount of the sound energy. 
     There are many applications, including the automotive field, where sound absorption and attenuation is important to the consumer. The interior surface of a vehicle is commonly covered or lined with panels of sound absorbent material that present an aesthetically appealing appearance and also absorb or attenuate exterior sound. Molded fiber glass panels and foam liners are examples of such materials used in vehicles that are able to attenuate sound over a wide range of frequencies. Conventionally, such panels are either single or multi-layered structures of fiberglass or foam material having an outside covering layer visible in the cabin, typically of a cloth or soft material, and a backing layer of a relatively stiff material that is adhered to the interior of the vehicle cabin. 
     Automotive headliners have evolved from simple fabric or fiberglass covered foam to improved designs specifically adapted to provide sound absorption and attenuation in a vehicle. Yet, there remains a need for improved sound barriers that attenuate sound over a broad range of frequencies or, alternatively, may be tuned for maximum sound attenuation in a specific frequency. The present invention utilizes a fibrous pad as the sound attenuation component of a trim panel that may be tuned to attenuate sound in a specific frequency range. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, a tunable sound absorbing fibrous pad is formed by applying a film to a fibrous sheet or batt of material using heat and pressure. The sound absorbing fibrous pad is preferably formned in a continuous process such as a webline, where linespeed, heat, and pressure may be varied. In operation, the heat and pressure applied to the fibers cause the fibers of the fibrous batt to penetrate the film and create perforations within the film and the linespeed of the process will determine the exposure time of the film to the heat and pressure. Heat from the process can “blow open” the perforations caused by the geometric surface of the fibrous pad and create larger holes corresponding to higher process temperatures. These variables in combination will determine the size and number of perforations in the film. The size and number of perforations control the air flow resistance of the film and thus, the sound absorbing and attenuation properties of the sound absorbing fibrous pad. Accordingly, the sound absorbing and attenuation characteristics of the sound absorbing fibrous pad can be modified during the fabrication of the sound absorbing fibrous pad by varying the process variables. 
     An object of the present invention is to create a sound absorbing pad that may be tuned to absorb sound in a desired frequency range. As discussed previously, the processing of the pad may be manipulated such that the pad may be tuned to absorb sound at predetermined frequencies. Specifically, the material of the present invention may be tailored to attenuate problematic sound frequencies produced in a vehicle cabin. 
     Another object of the present invention is to create a sound absorbing pad that has been optimized to absorb and attenuate as much sound over as wide a range of frequencies as possible for the type of material being used. 
     A further object of the present invention is to provide an interior trim pad that is made predominantly of synthetic fibers so that the fibrous pad can be recycled or made recyclable. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The various advantages of the present invention will become apparent to those skilled in the art after reading the following specification and by reference to the drawings, in which: 
     FIG. 1 is a diagrammatic schematic cross-sectional view of the sound absorbing pad made according to the teachings of the preferred embodiment of the present invention; 
     FIG. 2 is a diagram of the process used to fabricate the sound absorbing pad shown in FIG. 1 made according to the teachings of the preferred embodiment of the present invention; 
     FIG. 3 is a bar chart illustrating the air flow resistance of different materials manufactured with different process variables using the method according to the preferred embodiment of the present invention; 
     FIG. 4 is a bar chart illustrating the surface porosity of different materials manufactured with different process variables using the method according to the preferred embodiment of the present invention; and 
     FIG. 5 is a graph illustrating the sound attenuation performance enhancements of the present invention according to the preferred embodiment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The following description of the present embodiment is merely exemplary in nature and is in no way intended to limit the invention, its application, or its uses. Moreover, while the preferred embodiment describes a sound absorbing fibrous pad designed to operate with a vehicle, the following description is intended to adequately teach one skilled in the art to make and use the sound absorbing fibrous pad for other applications. 
     FIG. 1 is a partial cross section of the sound absorbing fibrous pad  10  of the present invention. The sound absorbing pad  10  includes a fibrous batt  12  and a film  14  coupled to one side of the fibrous batt  12 . In alternate embodiments of the present invention, the film  14  may be applied to both sides of the fibrous batt  12 . The fibrous batt  12  is preferably comprised of virgin or recycled polymeric fibers such as polyethylene terepthalate (PET), polyester, polypropylene, and nylon, but may also be comprised of natural fibers such as cotton. The fibers of the fibrous batt preferably have a diameter between 10-100 microns with the average effective diameter of the fibers being approximately 22 microns and the fibrous batt  12  is preferably 5-30 mm thick. In one embodiment of the sound absorbing pad  10 , the fibrous batt  12  includes binding polymeric fibers with a relatively low melting point when compared to the remaining fibers in the fibrous batt  12 . These binding fibers will melt at a lower temperature than the remaining fibers in the fibrous batt  12 , coupling the fibers of the fibrous batt  12  and ensuring that the fibers of the fibrous batt  12  are firmly bound. The film  14  is preferably comprised of polyethylene, polyester, or PET but may be any type of film that is thermoformable or thermosettable. The use of polymeric and thermoformable materials for the fibrous batt  12  and the film  14  will aid in the recycling of the sound absorbing pad  10 . 
     The film  14  is overlaid onto the fibrous batt  12  preferably in a continuous process such as a webline which will be more fully described below. Heat and pressure are applied to the film  14  during processing, causing the fibers of the fibrous batt  12  to penetrate the film  14  and form microruptures or perforations  16 . The size and number of these perforations  16  determine the sound absorbing and attenuating characteristics of the resultant sound absorbing pad  10 . Referring to FIG. 1, the film side of the sound absorbing pad  10  is positioned to face incident sound waves  18 . The sound waves  18  contact the film  14  and are conducted through the film  14  via the perforations  16 . The energy of the sound waves  18  is then transmitted to the fibers of the fibrous batt  12 . The fibers will absorb the sound energy as kinetic energy and oscillate until the energy is dissipated as heat. The sound energy is further dissipated through viscous losses (air shearing and movement) that also result in heat. Furthermore, the sound upon entering the fibrous batt  12  is trapped within the fibrous batt  12  and continuously reflects off the film  14 , as shown by arrows  20 . This reflection multiplies the damping and attenuation effects of the fibers in the fibrous batt  12 , providing a superior sound absorbing pad. 
     The process for forming the sound absorbing pad  10  is a continuous process and can be seen in FIG.  2 . The fibrous batt  12  under tension and the film  14  under tension are fed between a hot roller  22  and a cold roller  24  that laminate the fibrous batt  12  and film  14 . The fibrous batt  12  and film  14  are preferably unwound with torque or tension controlled unwinds with or without tension feedback. Electric motors, magnetic clutches, and mechanically weighted unwinds may be used to unwind the fibrous batt  12  and film  14 . 
     The hot roller  22  and cold roller  24  apply pressure or pinch the film  14  and fibrous batt  12  together to create the lamination. The hot roller  22  and cold roller  24  are preferably forced together by a pressure device such as a hydraulic or pneumatic piston but any other type of pressure generating device is within the scope of the present invention. The hot roller  22  is heated to a predetermined temperature to soften the film  14  so that the fibers of the fibrous batt  12  can penetrate the film  14  to create the perforations  16 . The cold roller  24  cools the fibrous batt  12  to prevent it from transforming into a block of molten plastic. The temperatures of the hot roller  22  and the cold roller  24  are balanced to create a temperature gradient such that only the film at the interface of the fibrous batt  12  enters the molten stage, allowing the fibers of the fibrous batt  12  to penetrate the film  14  and create the perforations  16 . The resulting sound absorbing pad  10  is porous and has excellent sound absorptive and attenuation properties along with a desirable resilient feel. 
     As discussed above, a continuous process is used to form the sound absorbing pad  10 . Thus, the hot roller  22  and cold roller  24  are turning at a certain line speed or surface speed. The line speed determines the exposure time of the film  14  and fibrous batt  12  to the applied heat and pressure. Accordingly, the line speed in combination with the heat and pressure applied to the film  14  will determine the size and number of the perforations  16  in the film  14 . 
     The resultant size and number of perforations  16  formed during processing change the sound absorbing pad&#39;s  10  air flow resistance and thus its sound absorption and attenuation characteristics. The process may be tuned to create the optimum air flow resistance in order to maximize the overall acoustic absorption of the sound absorbing pad  10  or tuned for a maximum absorption in a specific sound frequency range. 
     FIG. 3 is a bar chart showing the air flow resistance of the sound absorbing pad  10  for different film  14  materials laminated to a polymeric post industrial or recycled fibrous batt  12  at different line speeds. Maximum or 100% linespeed is defined as 80 feet per minute. The first bar  26  is a measurement of the air flow resistance of the sound absorbing pad  10  with Dow 933 film run at 15% speed at 370° F. (sample 14 seen in Table 1). The second bar  28  is a measurement of the air flow resistance of the sound absorbing pad  10  with 1 mil EVA Blend Coax Laminate film run at 10% speed at 370° F. (sample 12 seen in Table 1). The third bar  30  is a measurement of the air flow resistance of the sound absorbing pad  10  with 1 mil EVA Blend Coax Laminate film run at 15% speed at 372° F. (sample 13 seen in Table 1). The pinch pressure between the hot roller  22  and cold roller  24  was kept constant for all three runs. As can be seen from the bar chart, the air flow resistance of the sound absorbing pad  10  will vary with linespeed. 
     Referring to the bar chart of FIG. 4, surface porosities corresponding to the air flow resistance values of FIG. 3 are detailed with reference to the sound absorbing pad  10  having different films  14  laminated to the fibrous batt  12 . The first bar  32  is a measurement of the surface porosity of Dow 933 run at 15% speed at 370° F. (sample 14) and corresponds to bar  26  of FIG.  3 . The second bar  34  is a measurement of the surface porosity of 1 mil EVA Blend Coax Laminate film run at 10% speed at 370° F. (sample 12) and corresponds to bar  28  of FIG.  3 . The third bar  36  is a measurement of the surface porosity of 1 mil EVA Blend Coax Laminate film run at 15% speed at 372° F. (sample 13) and corresponds to bar  30  of FIG.  3 . While specific test results have been detailed in this paragraph, the linespeed, temperature and pressure may be varied to attain a wide range of air flow resistances and porosities. The above examples were included to illustrate that the variation in process variables will result in a variation of surface porosity and air flow resistance. Accordingly, the acoustic resistance of the film  14  and thus, the sound absorption of the sound absorbing pad  10 , will also vary. 
     Generally, a sound absorbing pad with a film with lower hole density (1-400,000 holes per m 2 ) will have better sound attenuation and absorbing characteristics in the low frequency ranges (200-1200 Hz) and a sound absorbing pad with film with a higher hole density (&gt;400,000 holes per m 2 ) will have better sound attenuation characteristics in the higher frequency ranges (&gt;1200 Hz). The optimum hole density for sound absorption over a wide frequency range is usually somewhere in the middle hole density ranges i.e. 400,000 holes per m 2 . 
     FIG. 5 is a graph of the sound absorption characteristics vs. sound frequency for a sound absorbing pad having a virgin batt with no film and a sound absorbing pad and films that have been perforated by the fibrous batt during processing. The term “up” means that the film side of the material is tested towards the incident sound waves and the term “down” means that the non-film side is tested towards the incident sound waves. As can be seen from the graphs the sound absorbing characteristics of the sound absorbing pad  10  have been greatly increased by the method of the present invention. Line  38  represents a sound absorbing pad having a virgin fibrous batt of VTP03208. Lines  40 ,  42 ,  44 ,  45 ,  46 , and  48  represent the sound absorbing characteristics of Dow 933 and 1 mil EVA Blend Coax Laminate films laminated by the method of the present invention to a polymeric fibrous batt  12  to form perforations  16  in the films. Lines  40  and  48  correspond to bar  26  of FIG. 3, bar  32  of FIG. 4, and sample 14 of Table 1. Lines  42  and  46  correspond to bar  28  of FIG. 3, bar  34  of FIG. 4, and sample 12 of Table 1. Lines  44  and  45  correspond to bar  30  of FIG. 3, bar  36  of FIG. 4, and sample 13 of Table 1. As can be seen from the graph and the following table, the films processed by the method of the present invention have higher sound absorption coefficients than the virgin VTP03208 batt. 
     
       
         
               
             
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Variation of sound absorption characteristics of the fibrous pad 10, having fibrous batt 
               
               
                 12 and film 14, in response to a variation in process variables. The term “up” means that the 
               
               
                 film side of the material is tested towards the incident sound waves and the term “down” means 
               
               
                 that the non-film side is tested towards the incident sound waves. The speed is defined as a 
               
               
                 percentage of total speed which is 80 feet per minute. The defined thickness is the thickness of 
               
               
                 the fibrous batt 12. 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Dow 933 
                 Dow 933 
                 Dow 933 
                 Dow 933 
                 Dow 933 
                 Dow 933 
                 Dow 933 
                 Dow 933 
                 Dow 933 
                 Dow 933 
               
               
                   
                 down, 10% 
                 up, 10% 
                 down, 10% 
                 up, 10% 
                 down,10% 
                 up, 10 % 
                 down, 10% 
                 up, 10% 
                 down, 15 % 
                 up, 15% 
               
               
                   
                 speed, 18 
                 speed, 18 
                 speed, 18 
                 speed, 18 
                 speed, 18 
                 speed, 18 
                 speed, 18 
                 speed, 18 
                 speed, 18 
                 speed, 18 
               
               
                   
                 mm thick 
                 mm thick 
                 mm thick 
                 mm thick 
                 mm thick 
                 mm thick 
                 mm thick 
                 mm thick 
                 mm thick 
                 mm thick 
               
               
                   
                 350° F. 
                 350° F. 
                 350° F. 
                 350° F. 
                 350° F. 
                 350° F. 
                 350° F. 
                 350° F. 
                 350° F. 
                 350° F. 
               
               
                 Freq. 
                 sample 1 
                 sample 1 
                 sample 2 
                 sample 2 
                 sample 3 
                 sample 3 
                 sample 4 
                 sample 4 
                 sample 5 
                 sample 5 
               
               
                   
               
               
                 200 
                 0.16 
                 0.18 
                 0.15 
                 0.12 
                 0.14 
                 0.09 
                 0.11 
                 0.09 
                 0.15 
                 0.13 
               
               
                 250 
                 0.18 
                 0.18 
                 0.18 
                 0.19 
                 0.16 
                 0.19 
                 0.16 
                 0.19 
                 0.14 
                 0.20 
               
               
                 315 
                 0.19 
                 0.21 
                 0.18 
                 0.22 
                 0.19 
                 0.21 
                 0.19 
                 0.23 
                 0.23 
                 0.25 
               
               
                 400 
                 0.17 
                 0.19 
                 0.17 
                 0.22 
                 0.20 
                 0.22 
                 0.20 
                 0.22 
                 0.23 
                 0.23 
               
               
                 500 
                 0.23 
                 0.27 
                 0.22 
                 0.26 
                 0.24 
                 0.28 
                 0.22 
                 0.29 
                 0.27 
                 0.27 
               
               
                 630 
                 0.27 
                 0.33 
                 0.27 
                 0.36 
                 0.27 
                 0.35 
                 0.29 
                 0.35 
                 0.29 
                 0.31 
               
               
                 800 
                 0.28 
                 0.39 
                 0.29 
                 0.43 
                 0.28 
                 0.43 
                 0.29 
                 0.43 
                 0.32 
                 0.34 
               
               
                 1000 
                 0.35 
                 0.54 
                 0.36 
                 0.59 
                 0.35 
                 0.60 
                 0.36 
                 0.60 
                 0.39 
                 0.43 
               
               
                 1250 
                 0.39 
                 0.70 
                 0.41 
                 0.71 
                 0.39 
                 0.76 
                 0.40 
                 0.76 
                 0.42 
                 0.50 
               
               
                 1600 
                 0.43 
                 0.80 
                 0.44 
                 0.84 
                 0.43 
                 0.86 
                 0.45 
                 0.90 
                 0.47 
                 0.59 
               
               
                 2000 
                 0.46 
                 0.93 
                 0.45 
                 0.98 
                 0.47 
                 0.99 
                 0.47 
                 0.97 
                 0.49 
                 0.68 
               
               
                 2500 
                 0.49 
                 1.01 
                 0.48 
                 1.02 
                 0.52 
                 1.02 
                 0.51 
                 1.03 
                 0.50 
                 0.73 
               
               
                 3150 
                 0.51 
                 1.01 
                 0.52 
                 1.02 
                 0.54 
                 1.01 
                 0.56 
                 1.01 
                 0.53 
                 0.79 
               
               
                 4000 
                 0.54 
                 0.97 
                 0.54 
                 0.93 
                 0.57 
                 0.94 
                 0.59 
                 0.91 
                 0.55 
                 0.80 
               
               
                 5000 
                 0.57 
                 0.88 
                 0.59 
                 0.85 
                 0.61 
                 0.84 
                 0.61 
                 0.82 
                 0.55 
                 0.80 
               
               
                 6300 
                 0.61 
                 0.76 
                 0.64 
                 0.74 
                 0.66 
                 0.73 
                 0.68 
                 0.73 
                 0.62 
                 0.77 
               
               
                 8000 
                 0.67 
                 0.64 
                 0.68 
                 0.61 
                 0.72 
                 0.62 
                 0.74 
                 0.63 
                 0.67 
                 0.70 
               
               
                 10000 
                 0.66 
                 0.57 
                 0.68 
                 0.55 
                 0.76 
                 0.57 
                 0.75 
                 0.58 
                 0.68 
                 0.74 
               
               
                   
               
             
          
           
               
                   
                 Dow 933 
                 Dow 933 
                 Dow 933 
                 Dow 933 
                 1 mil EVA* 
                 1 mil EVA* 
                 mil EVA* 
                 1 mil EVA* 
                 1 mil EVA* 
                 1 mil EVA* 
               
               
                   
                 down, 15% 
                 up 15% 
                 down, 15% 
                 up 15% 
                 down, 10% 
                 10% speed, 
                 up 15% 
                 down 15% 
                 up 15% 
                 down 15 
               
               
                   
                 speed, 18 
                 speed, 18 
                 speed, 18 
                 speed, 18 
                 speed, 18 
                 18 mm 
                 speed, 18 
                 speed, 18 
                 speed, 18 
                 18 mm 
               
               
                   
                 mm thick 
                 mm thick 
                 mm thick 
                 mm thick 
                 mm thick 
                 mm thick 
                 mm thick 
                 mm thick 
                 mm thick 
                 thick 
               
               
                   
                 350° F. 
                 350° F. 
                 350° F. 
                 350° F. 
                 370° F. 
                 370° F. 
                 372° F. 
                 372° F. 
                 372° F. 
                 372° F. 
               
               
                 Freq. 
                 sample 6 
                 sampe 6 
                 sample 7 
                 sample 7 
                 sample 8 
                 sample 8 
                 sample 9 
                 sample 10 
                 sample 10 
                 sample 11 
               
               
                   
               
               
                 200 
                 0.21 
                 0.17 
                 0.15 
                 0.18 
                 0.14 
                 0.11 
                 0.14 
                 0.14 
                 0.10 
                 0.15 
               
               
                 250 
                 0.19 
                 0.20 
                 0.20 
                 0.20 
                 0.15 
                 0.16 
                 0.24 
                 0.16 
                 0.24 
                 0.18 
               
               
                 315 
                 0.21 
                 0.18 
                 0.20 
                 0.23 
                 0.20 
                 0.24 
                 0.27 
                 0.22 
                 0.26 
                 0.23 
               
               
                 400 
                 0.20 
                 0.21 
                 0.23 
                 0.23 
                 0.18 
                 0.22 
                 0.26 
                 0.22 
                 0.27 
                 0.22 
               
               
                 500 
                 0.27 
                 0.28 
                 0.27 
                 0.29 
                 0.22 
                 0.30 
                 0.35 
                 0.28 
                 0.33 
                 0.26 
               
               
                 630 
                 0.30 
                 0.32 
                 0.30 
                 0.31 
                 0.26 
                 0.37 
                 0.40 
                 0.31 
                 0.41 
                 0.29 
               
               
                 800 
                 0.31 
                 0.34 
                 0.31 
                 0.35 
                 0.27 
                 0.46 
                 0.S0 
                 0.33 
                 0.S0 
                 0.32 
               
               
                 1000 
                 0.39 
                 0.42 
                 0.38 
                 0.45 
                 0.35 
                 0.69 
                 0.68 
                 0.40 
                 0.70 
                 0.40 
               
               
                 1250 
                 0.41 
                 0.49 
                 0.41 
                 0.S0 
                 0.39 
                 0.85 
                 0.84 
                 0.43 
                 0.86 
                 0.43 
               
               
                 1600 
                 0.47 
                 0.57 
                 0.46 
                 0.57 
                 0.45 
                 0.98 
                 0.97 
                 0.47 
                 0.96 
                 0.48 
               
               
                 2000 
                 0.49 
                 0.63 
                 0.48 
                 0.65 
                 0.48 
                 1.03 
                 1.02 
                 0.53 
                 1.01 
                 0.51 
               
               
                 2500 
                 0.S0 
                 0.70 
                 0.49 
                 0.70 
                 0.52 
                 0.98 
                 1.02 
                 0.53 
                 1.02 
                 0.55 
               
               
                 3150 
                 0.52 
                 0.77 
                 0.51 
                 0.78 
                 0.56 
                 0.84 
                 0.95 
                 0.56 
                 0.97 
                 0.56 
               
               
                 4000 
                 0.54 
                 0.77 
                 0.52 
                 0.79 
                 0.61 
                 0.70 
                 0.86 
                 0.58 
                 0.83 
                 0.6t 
               
               
                 5000 
                 0.54 
                 0.72 
                 0.53 
                 0.75 
                 0.63 
                 0.62 
                 0.71 
                 0.63 
                 0.72 
                 0.65 
               
               
                 6300 
                 0.57 
                 0.70 
                 0.58 
                 0.69 
                 0.71 
                 0.54 
                 0.60 
                 0.70 
                 0.61 
                 0.71 
               
               
                 8000 
                 0.56 
                 0.60 
                 0.57 
                 0.61 
                 0.75 
                 0.47 
                 0.49 
                 0.74 
                 0.52 
                 0.80 
               
               
                 10000 
                 0.55 
                 0.59 
                 0.54 
                 0.61 
                 0.79 
                 0.46 
                 0.52 
                 0.80 
                 0.51 
                 0.83 
               
               
                   
               
             
          
           
               
                   
                   
                 1 mil EVA* 
                 1 mil EVA* 
                 1 mil EVA* 
                 1 mil EVA* 
                 1 mil EVA* 
                 Dow 933 
                 Dow 933 
                   
                   
               
               
                   
                   
                 up 15% 
                 up 10% 
                 down 10% 
                 up 15% 
                 down, 15% 
                 down, 15% 
                 up 15% 
                 Virgin 
                 Virgin 
               
               
                   
                   
                 speed, 18 
                 speed, 8 
                 speed, 8 
                 speed, 8 
                 speed, 8 
                 speed, 8 
                 speed, 8 
                 VTP02825 
                 VTP03208 
               
               
                   
                   
                 mm thick 
                 mm thick 
                 mm thick 
                 mm thick 
                 mm thick 
                 mm thick 
                 mm thick 
                 sample 15 
                 sample 16 
               
               
                   
                   
                 372° F. 
                 370° F. 
                 370° F. 
                 372° F. 
                 372° F. 
                 370° F. 
                 370° F. 
                 (no  
                 (no  
               
               
                   
                 Freq. 
                 sample 11 
                 sample 12 
                 sample 12 
                 sample 13 
                 sample 13 
                 sample 14 
                 sample 14 
                 film) 
                 film) 
               
               
                   
                   
               
               
                   
                 200 
                 0.12 
                 0.11 
                 0.13 
                 0.12 
                 0.11 
                 0.12 
                 0.13 
                 0.19 
                 0.08 
               
               
                   
                 250 
                 0.25 
                 0.15 
                 0.12 
                 0.15 
                 0.12 
                 0.13 
                 0.15 
                 0.22 
                 0.14 
               
               
                   
                 315 
                 0.26 
                 0.20 
                 0.13 
                 0.18 
                 0.16 
                 0.I5 
                 0.15 
                 0.26 
                 0.17 
               
               
                   
                 400 
                 0.27 
                 0.22 
                 0.15 
                 0.21 
                 0.18 
                 0.16 
                 0.16 
                 0.28 
                 0.18 
               
               
                   
                 500 
                 0.32 
                 0.33 
                 0.21 
                 0.31 
                 0.21 
                 0.22 
                 0.23 
                 0.31 
                 0.23 
               
               
                   
                 630 
                 0.40 
                 0.47 
                 0.26 
                 0.38 
                 0.25 
                 0.26 
                 0.29 
                 0.36 
                 0.27 
               
               
                   
                 800 
                 0.51 
                 0.38 
                 0.29 
                 0.36 
                 0.29 
                 0.27 
                 0.32 
                 0.36 
                 0.29 
               
               
                   
                 1000 
                 0.67 
                 0.42 
                 0.34 
                 0.43 
                 0.36 
                 0.34 
                 0.40 
                 0.44 
                 0.37 
               
               
                   
                 1250 
                 0.82 
                 0.59 
                 0.40 
                 0.57 
                 0.40 
                 0.39 
                 0.47 
                 0.49 
                 0.41 
               
               
                   
                 1600 
                 0.96 
                 0.82 
                 0.46 
                 0.76 
                 0.46 
                 0.45 
                 0.58 
                 0.53 
                 0.45 
               
               
                   
                 2000 
                 1.01 
                 0.95 
                 0.52 
                 0.89 
                 0.51 
                 0.49 
                 0.69 
                 0.53 
                 0.49 
               
               
                   
                 2500 
                 1.06 
                 0.99 
                 0.58 
                 1.00 
                 0.55 
                 0.54 
                 0.77 
                 0.52 
                 0.51 
               
               
                   
                 3150 
                 1.00 
                 1.00 
                 0.62 
                 1.10 
                 0.59 
                 0.57 
                 0.89 
                 0.52 
                 0.52 
               
               
                   
                 4000 
                 0.87 
                 0.85 
                 0.66 
                 1.00 
                 0.66 
                 0.61 
                 0.93 
                 0.51 
                 0.56 
               
               
                   
                 5000 
                 0.74 
                 0.76 
                 0.68 
                 0.97 
                 0.68 
                 0.63 
                 0.99 
                 0.49 
                 0.55 
               
               
                   
                 6300 
                 0.67 
                 0.65 
                 0.75 
                 0.91 
                 0.73 
                 0.72 
                 1.02 
                 0.49 
                 0.57 
               
               
                   
                 8000 
                 0.56 
                 0.52 
                 0.76 
                 0.70 
                 0.74 
                 0.75 
                 0.97 
                 0.46 
                 0.58 
               
               
                   
                 10000 
                 0.58 
                 0.45 
                 0.75 
                 0.60 
                 0.75 
                 0.82 
                 0.88 
                 0.43 
                 0.54 
               
               
                   
                   
               
               
                   
                 *1 mil EVA Blend Coax Laminate Film  
               
               
                   
                       AirFlow Resistance  KPA- Sec/m 3   
               
               
                   
                 Sample No. 14 Dow 15% speed    500  
               
               
                   
                 Sample No. 12 mil EVA Blend  2,900  
               
               
                   
                       Coax Laminate  
               
               
                   
                       Film 10% speed  
               
               
                   
                 Sample No. 13 1 mil EVA Blend  1,900  
               
               
                   
                       Coax Laminate  
               
               
                   
                       Film 15% speed  
               
               
                   
                       Cells per m 2   
               
               
                   
                 Sample No. 14 Dow 15% speed  800,000  
               
               
                   
                 Sample No. 12 1 mil EVA Blend  100,000  
               
               
                   
                       Coax Laminate  
               
               
                   
                       Film 10% speed  
               
               
                   
                 Sample No.13 1 mil EVA Blend  170,000  
               
               
                   
                       Coax Laminate  
               
               
                   
                       Film 15% speed  
               
             
          
         
       
     
     It is to be understood that the invention is not limited to the exact construction illustrated and described above, but that various changes and modifications may be made without departing from the spirit and scope of the inventions as defined in the following claims.