Automotive dash insulators containing viscoelastic foams

[0001] This application claims the benefit of U.S. Provisional Application No. 60/535,933, filed Jan. 12, 2004. The disclosure of the above application is incorporated herein by reference.

[0002] The present invention relates generally to a sound insulating system. More particularly, the present invention relates to sound insulator systems containing viscoelastic foams.

[0003] Automotive makers have endeavored to reduce the overall noise and vibration in vehicles. Limiting noise, vibration, and harshness (i.e., “NVH”) has become an important consideration in vehicle designs. Previously, engine noise typically dominated the overall vehicle noise. Other noise sources, such as from tires, wind and exhaust have also become as important to reduce as engine noise. More recently, interior vehicle noise constriction has been a direct result of consumer demands to reduce the noise in the vehicle.

[0004] Accordingly, significant efforts have been directed to reduction of interior vehicle noise. One of these efforts has been to use a barrier concept, also referred to as a dashmat or dash insulator system. These dashmats are used to reduce noise from the engine to the interior of the vehicle. Typically such dashmats are placed on or adjacent a substrate, such as a firewall to reduce the amount of noise passing from the engine through the firewall to the vehicle interior. A general description of dashmat technology can be found in U.S. Patent Application Publication No. 2003/0180500 A1, the entire specification of which is expressly incorporated herein by reference.

[0005] Prior dashmats are typically made of a decoupler, usually made of foam (slab or cast foam) and a barrier, typically made of thermoplastic polyolefin (TPO) or ethylene vinyl acetate sheet (EVA). These dashmats are all intended to reduce overall engine compartment noise. Such barrier type dashmats have typically been relatively heavy, in order to produce the desired noise reduction results.

[0006] It is believed that a significant portion of a dashmat's performance relies on the properties of the foam. Foam performance is generally considered to be a function of the foam's transmission loss, absorption, modulus, and damping characteristics.

[0007] More recently, lightweight dashmats have been used. The lightweight concept utilizes absorptive material, such as shoddy cotton. Rather than blocking the engine noise, the goal of this type of dashmat is to absorb and dissipate the engine noise as it travels from the engine compartment to the vehicle interior. These lightweight dashmat systems also decrease the overall weight of the vehicle. A general description of these types of lightweight dashmat systems can be found in U.S. Pat. Nos. 6,145,617 and 6,296,075, the entire specifications of which are expressly incorporated herein by reference.

[0008] The primary function of either type of dashmat is to reduce noise levels in the vehicle's interior. Traditionally, it was believed that blocking the noise in accordance with the mass law provides the best noise transmission loss and noise reduction. Transmission loss and noise reduction are typical measurement parameters used to quantify the performance of the dashmat system.

[0009] Although conventional dashmats have been somewhat successful in reducing noise levels in the vehicle's interior, they have not been completely satisfactory. More specifically, the insulation foam (i.e., the decoupler) has been relatively ineffective in that it does not possess suitable absorptive acoustic properties. Thus, the noise, regardless of origin, is either not blocked, dissipated or otherwise reduced enough as it travels through the dashmat and into the vehicle's interior. Further, earlier insulation foams are less effective at preventing noise due to vibration of the substrate or barrier layer.

[0010] Accordingly, it would be desirable to provide dashmats that have enhanced transmission loss performance characteristics so as to be operable to reduce both engine compartment noise coming through the firewall and noise that comes into the passenger compartment from other sources during vehicle operation.

[0011] According to a first embodiment of the present invention, there is provided a sound insulating system, comprising a sound-absorbing layer including an absorption coefficient in the range of about 0.2 to about 1.0, and a damping loss factor in the range of about 0.3 to about 2.0.

[0012] According to an alternate embodiment of the present invention, there is provided a sound insulating system, comprising a sound-absorbing layer including an absorption coefficient in the range of about 0.2 to about 1.0, and a damping loss factor in the range of about 0.3 to about 2.0. The system further comprises a barrier layer substantially impermeable to fluid flow therethrough connected to said sound-absorbing layer.

[0013] According to an alternate embodiment of the present invention there is provided a sound insulating system, comprising a sound-absorbing layer comprising a viscoelastic foam. The viscoelastic foam includes an absorption coefficient in the range of about 0.7 to about 1 at frequencies in the range of about 1000 Hz to about 6000 Hz, and a damping loss factor in the range of about 0.4 to 1.6. The system further comprises a barrier layer substantially impermeable to fluid flow therethrough connected to said viscoelastic foam.

[0014] The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:

[0015] FIG. 1 is a sectional view of an illustrative sound insulating system, in accordance with the general teachings of the present invention;

[0016] FIG. 1A is a sectional view of the sound insulating system depicted in FIG. 1 attached to a substrate, in accordance with one embodiment of the present invention;

[0017] FIG. 2 is a graphical illustration comparing the normal incidence absorption coefficient characteristics of the illustrative sound-absorbing layers, in accordance with one embodiment of the present invention;

[0018] FIG. 3 is a schematic illustration of an illustrative test setup to determine elastic modulus and damping of the illustrative sound-absorbing layers, in accordance with one embodiment of the present invention;

[0019] FIG. 4 is a graphical illustration comparing the transmission loss characteristics of the sound insulating systems in accordance with the present invention and conventional sound insulting systems;

[0020] FIG. 5 is a graphical illustration comparing the surface weight characteristics of the sound insulating systems in accordance with the present invention and conventional sound insulting systems;

[0021] FIG. 6 is a graphical illustration comparing the transmission loss characteristics of a sound insulating system in accordance with the present invention and a conventional sound insulting system in relationship to a pre-determined target profile, in accordance with one embodiment of the present invention;

[0022] FIG. 7 is a graphical illustration comparing the decibel improvement in average noise reduction characteristics of a sound insulating system of the present invention and conventional sound insulting systems, in accordance with one embodiment of the present invention;

[0023] FIG. 8 is a graph showing damping test results;

[0024] FIG. 9 is a graph showing damping test results;

[0025] FIG. 10 is a graph showing insertion loss test results; and

[0026] FIG. 11 is a graph showing damping test results.

[0027] The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.

[0028] FIG. 1 is a cross-sectional view of one embodiment of the present invention. As shown in FIG. 1, there is a sound insulating system, generally shown at 10. The sound insulating system 10 preferably comprises a multilayer system. The sound insulating system 10 preferably comprises a sound-absorbing layer generally indicated at 12. An optional barrier layer generally indicated at 14 is preferably adjacent to the sound-absorbing layer 12. It should be appreciated that system 10 is preferably operable to be fastened or otherwise attached, either removably or permanently, to an optional substrate generally indicated at 14, such as a firewall, as shown in FIG. 1A. The substrate 16 is preferably adjacent to the sound-absorbing layer 12 and spaced and opposed from the barrier layer 14.

[0029] The system 10 preferably provides a multilayer dashmat that is preferably used to reduce noise transmission to the interior of the vehicle through the front-of-dash panel. In addition to the noise-blocking feature, the system 10 preferably reduces noise levels within the vehicle interior through sound absorption. Additionally, the system 10 preferably can be used in the engine compartment to reduce noise exiting the engine compartment to the exterior of the vehicle. The system 10 also preferably enhances the sound quality perception for interior and/or exterior environments. The system 10 can also be incorporated into other automotive components such as, but not limited to, liners for wheel wells, fenders, engine compartments, door panels, roofs (e.g., headliners), floor body treatments (e.g., carpet backing), trunks and packaging shelves (e.g., package tray liners). Furthermore, the system 10 can be incorporated into non-automotive applications.

[0030] The sound-absorbing layer 12 preferably comprises a foam material 18. The foam material 18 preferably comprises viscoelastic foam, more preferably viscoelastic flexible foam, and still more preferably viscoelastic flexible polyurethane foam. Viscoelastic foam, also referred to as memory or temper foam, is substantially open-celled and is generally characterized by its slow recovery after compression.

[0031] The use of viscoelastic foam in accordance with the present invention in a dashmat system can also possibly be used as a replacement for vibration damping materials, commonly referred to as mastic.

[0032] Although viscoelastic foams are preferred in the practice of the present invention, other foams can be used, either alone or in combination, that have the requisite properties to be described herein. Accordingly, the foam material 18 can comprise any natural or synthetic foam, both slab and molded. The foam material 18 can be open or closed cell or combinations thereof. The foam material 18 can comprise latex foam polyolefin, polyurethane, polystyrene, polyester, and combinations thereof. The foam material 18 can also comprise recycled foam, foam impregnated fiber mats or micro-cellular elastomer foam. Additionally, the foam material 18 can include organic and/or inorganic fillers. Furthermore, additional additives may be incorporated into the foam material 18, such as, but not limited to, flame retardants, anti-fogging agents, ultraviolet absorbers, thermal stabilizers, pigments, colorants, odor control agents, and the like.

[0033] In accordance with a preferred embodiment of the present invention, the foam material 18 has a relatively high absorption coefficient. Without being bound to a particular theory of the operation of the present invention, it is believed that a relatively high absorption coefficient will increase the overall transmission loss through dissipation of the sound within the foam material 18.

[0034] FIG. 2 shows sound absorption of various foams. VE refers to viscoelastic foam. PCF is a density measure referring to lb/ft³. The specific VE foam used was FOAMEX H300-10N. The slab foam was Melamine and the cast foam was polyurethane foam. In accordance with a preferred embodiment of the present invention, the foam material 18 has an absorption coefficient of about 0.2 or greater, more preferably about 0.4 or greater, still more preferably about 0.7 or greater, and most preferably about 1.0. In the most preferred embodiment, the absorption coefficient is in the range of between about 0.7 and 1 at frequencies in the range about 1000 Hz to about 6000 Hz.

[0035] In accordance with a preferred embodiment of the present invention, the foam material 18 has a relatively low elastic modulus. Without being bound to a particular theory of the operation of the present invention, it is believed that a relatively low elastic modulus will allow the foam material 18 to contact the substrate 16 (e.g., the firewall or the vehicle's steel structure) more uniformly and prevent flanking noise from entering the vehicle's interior. Thus, it is preferred to have a relatively lower modulus. A lower modulus allows the foam layer 18 to conform more readily to a substrate. If the modulus is too high, the foam 18 will be too stiff and not easily conform to the substrate. However, the modulus should not be so low as to not have structural integrity.

[0036] In general, the minimum modulus would be sufficient for the foam cells to retain their structure. In accordance with a preferred embodiment of the present invention, the foam material 18 has an elastic modulus in the range of about 4×10³ Pa to about 1×10⁶ Pa.

[0037] In another preferred embodiment, the modulus is in the range of about 1×10⁴ to about 1×10⁵. These ranges are measured according to test setup shown in FIG. 3.

[0038] In accordance with a preferred embodiment of the present invention, the foam material 18 has a relatively high damping loss factor (tan delta). Without being bound to a particular theory of the operation of the present invention, it is believed that a relatively high damping loss factor helps reduce vibration in the vehicle's steel structure which will increase the overall transmission loss of the dashmat. In accordance with a preferred embodiment of the present invention, the foam material 18 has a damping loss factor (tan delta) of about 0.3 or greater, more preferably about 0.4 or greater, still more preferably about 1.0 or greater.

[0039] In accordance with another preferred embodiment of the present invention, the foam material 18 has a damping loss factor (tan delta) in the range of about 0.3 to about 2.0, more preferably in the range of about 0.4 to about 2.0, and still more preferably in the range of about 0.4 to about 1.6. These values are measured according to test setup shown in FIG. 3.

[0040] By way of a non-limiting example, foam materials that satisfy the above requirements include Dow experimental viscoelastic polyurethane foams #76-16-06 HW, #76-16-08HW, #76-16-10HW, #056-53-01HW, and #056-53-29HW; Foamex 2 pound per cubic foot (pcf) and Foamex H300-10N 3 pcf viscoelastic foams (readily commercially available); Carpenter 2.5 pcf viscoelastic foam (readily commercially available); and Leggett and Platt viscoelastic foams 25010MF and 30010MF (readily commercially available).

[0041] The thickness of the sound-absorbing layer 12 can vary depending on the particular application. While it is preferred that the thickness be between about 6 mm to about 100 mm, more preferably about 12 mm to about 50 mm, and still more preferably about 12 mm to about 25 mm, it will be appreciated that the thickness can vary, even outside these ranges depending on the particular application. The thickness has a bearing on the stiffness of the sound-absorbing layer 12. It will also be appreciated that the thickness of the sound-absorbing layer 12 can vary and can be non-uniform.

[0042] Further, it is to be understood that the sound-absorbing layer 12 can comprise combinations of materials adjacent one another. That is, the sound-absorbing layer 12 can comprise more than one sublayer of either a similar or dissimilar material.

[0043] The normal incidence absorption coefficient of the sound-absorbing layers of the present invention was measured according to ASTM E1050. Referring to FIG. 2, there is shown the normal incidence absorption coefficient profiles of the three of the sample foams, Dow #76-16-10HW and #76-16-08HW, and Leggett & Platt 30010MF. It should be noted that these three sample foams fall into a preferred range of absorption coefficient, i.e., around the 1000 to 8000 Hz range.

[0044] The elastic modulus and damping of the sound-absorbing layers of the present invention were measured using a plate, shaker, and two accelerometers. Referring to FIG. 3, there is shown a schematic illustration of an illustrative test setup. The transmissibility was measured between accelerometer 1 and accelerometer 2 and the first resonant frequency of the system is determined. The elastic modulus was then be determined by: $E=\frac{{\omega }^2\mathrm{mt}}{\mathrm{WL}}$

• • [0045] wherein:
    • [0046] E=elastic modulus (Pa)
    • [0047] ω=angular frequency (rad/s)
    • [0048] m=plate mass (kg)
    • [0049] t=foam thickness (m)
    • [0050] W=plate width (m)
    • [0051] L=plate length (m)

[0052] The damping was measured from the transmissibility using the half power bandwidth technique.

[0053] The barrier layer 14 preferably comprises a relatively thin substantially impermeable layer. The barrier layer 14 is substantially impermeable to fluid flow therethrough. In accordance with a preferred embodiment of the present invention, the barrier layer 14 comprises a thermoplastic olefin. By way of a non-limiting example, the barrier layer 14 preferably comprises sheets of acrylonitrile-butadiene-styrene, high-impact polystyrene, polyethylene teraphthalate, polyethylene, polypropylene (e.g., filled polypropylene), polyurethane (e.g., molded polyurethane), ethylene vinyl acetate, and the like. The barrier layer 14 can also include natural or synthetic fibers for imparting strength. The barrier layer 14 is also preferably shape formable and retainable to conform to the sound-absorbing layer 12 and/or the substrate 16 for any particular application. Additionally, the barrier layer 14 may include organic and/or inorganic fillers. Furthermore, additional additives may be incorporated into the barrier layer 14 composition, such as but not limited to flame retardants, anti-fogging agents, ultraviolet absorbers, thermal stabilizers, pigments, colorants, odor control agents, and the like.

[0054] In accordance with a preferred embodiment of the present invention, the barrier layer 14 is preferably comprised of about 15 wt. % polypropylene, about 25 wt. % thermoplastic elastomer (e.g., Kraton®, commercially available), about 55 wt. % calcium carbonate filler, and about 5 wt. % additives (e.g., processing aids, colorants, and the like).

[0055] In accordance with a preferred embodiment of the present invention, the barrier layer 14 preferably has a specific gravity of about 0.9 or greater, more preferably about 1.4 or more, and still more preferably about 1.6 or greater. It is also preferable that the barrier layer 14 have a surface weight of about 0.1 kg/m² or greater. It is more preferred that the barrier layer 14 have a surface weight of greater than 0.4 kg/m².

[0056] As with the absorbing layer 12, the barrier layer 14 can have varying thickness. It is preferred that the thickness of the barrier layer be between 0.1 and 50 mm. Again, it is to be understood that the thickness can be varied, even outside the preferred range, depending on the particular application and the thickness can also be non-uniform.

[0057] While a single barrier layer 14 is shown, it is to be understood that multiple barrier layers 14 of varying thickness may be used. Thus, each barrier layer 14 may comprise more than one sublayer of either a similar or dissimilar material.

[0058] As noted, the barrier layer 14 is preferably shape formable and retainable in order to conform the shape of the system 10 to the substrate 16 for any application. In order to combine the sound-absorbing layer 12 with the barrier layer 14, any suitable fabrication technique may be used. Some such examples include connecting the various layers by heat laminating, or by applying adhesives between the various layers. Such adhesives may be heat activated. The various layers may also be adhered during the process of shape forming by heating the layers and then applying pressure in the forming tool, or by applying adhesive to the layers and then applying pressure in the forming tool.

[0059] The system 10 could also be constructed in a cast foam tool by inserting the barrier layer 14 material, such as a polymer film, into the center section of a mold and then injecting foam, such as viscoelastic polyurethane foam into both sides of the tool. The system 10 can also be formed by creating the sound-absorbing layer 12 and barrier layer 14 jointly and/or independently and then securing them by conventional methods, for example, using mechanical fasteners, heat fusing, sonic fusing, and/or adhesives (e.g., glues, tapes, and the like).

[0060] The substrate 16 can be comprised of any number of suitable materials. By way of a non-limiting example, the substrate 16 can be comprised of metals, natural fiber mats, synthetic fiber mats, shoddy pads, flexible polyurethane foam, rigid polyurethane foam, and combinations thereof.

[0061] With respect to fastening or otherwise attaching the sound-absorbing layer 12 to the substrate 16, any number of suitable methods can be employed. By way of a non-limiting example, mechanical fasteners, heat fusing, sonic fusing, and/or adhesives (e.g., glues, tapes, and the like) may be used.

[0062] Analysis was conducted in order to demonstrate the performance benefit of using the viscoelastic foam of the present invention in a dashmat over the traditional lightweight slab foam construction. The dashmat performance was determined by examining the transmission loss of a 0.8 mm steel panel and dashmat system (i.e., viscoelastic foam sound-absorbing layer and a thermoplastic olefin barrier layer). The transmission loss was computed using a simulation method called statistical energy analysis. This analysis utilized the material properties of the foam and other materials in order to compute the transmission loss and other quantities within the frequency range of 100 to 10,000 Hz.

[0063] The design variables in the analysis were: (1) Foam types: (a) traditional lightweight slab foam; (b) Dow viscoelastic foam (formulation #76-16-10HW); and (c) Foamex 2 pcf viscoelastic foam; (2) Barrier layer (e.g., thermoplastic olefin) specific gravity: 1.2, 1.4, and 1.6; and (3) Foam thickness: 13 mm and 18 mm. It should be noted that the barrier layer thickness was held constant at 2.4 mm.

[0064] The dashmat construction was simulated according to the typical sound-absorber/barrier layer system, as generally shown in FIG. 1A. The transmission loss was computed for each combination of the design variables.

[0065] Referring to FIG. 4, there is shown a comparison between configurations using various foam types and various specific gravity barrier layers at 18 mm foam thickness. The test procedure is described below. As shown in FIG. 4, changing the foam type to either of the viscoelastic foams improves the transmission loss of the dashmat system, especially in the region of 1000 to 10,000 Hz. Furthermore, changing the foam type to either of the viscoelastic foams increases the transmission loss greater than increasing the specific gravity of the barrier layer while using slab foam.

[0066] In order to compare the performance of the design variables more effectively, a target configuration was chosen. The target configuration was chosen to be that of 18 mm traditional slab foam with a barrier layer having a 1.4 specific gravity. All other viscoelastic configurations were compared to the performance of this target configuration.

[0067] The samples were placed over a 0.8 mm thick steel plate, and the assembly was inserted into the wall between the reverberation chamber and the semi-anechoic chamber. Noise was generated in the reverberation room using a speaker, and the sound pressure level was measured using four microphones placed at a distance of 1.17 m from the steel plate. An array of twelve microphones was placed in the semi-anechoic chamber at a distance of 0.76 m from the outer foam side of the sample. Noise reduction was calculated using Equation 1, in accordance with the general protocol of SAE J1400. The result of the noise reduction test is shown in FIG. 4.
NR=(average SPL₁)−(average SPL₂)  Equation 1

• • [0068] Where:
    • [0069] SPL₂=Anechoic Sound Pressure level (dB)
    • [0070] SPL₁=Reverberation Sound Pressure Level (dB)

[0071] Referring to FIG. 5, there is shown the surface weight of all the viscoelastic foam configurations in comparison to the target surface weight. The surface weight (i.e., the mass of the dashmat construction divided by the area of the panel) was used to compare the relative weight of each configuration. Lower weight in the dashmat configuration is desirable for improved vehicle fuel economy, engine performance, and the like. Three of viscoelastic foam configurations had a lower surface weight than the target. These are: (1) 13 mm Dow viscoelastic foam (formulation #76-16-10HW) with 1.2 specific gravity; (2) 18 mm Foamex 2 pcf viscoelastic foam; and (3) 13 mm Foamex 2 pcf viscoelastic foam.

[0072] Referring to FIG. 6, there is shown two of the viscoelastic foam configurations in comparison to the target configuration. These two configurations demonstrate the viscoelastic foam's ability to increase the dashmat transmission loss with similar or lower weight.

[0073] Testing was also completed on a GM truck vehicle dash section to determine the noise reduction capability of the viscoelastic foam in comparison to traditional slab foam dashmats. Because transmission loss is difficult to measure for a vehicle section, noise reduction was used instead of transmission loss. The vehicle section was placed in a wall between a reverberation room and an anechoic chamber. Sound pressure level measurements were made in both rooms to compute the noise reduction.

[0074] Referring to FIG. 7, there is shown the results from the vehicle dash section testing with three different dashmats. The three dashmats tested can be described by: (1) Optimized 1.4 specific gravity dashmat, i.e., a dashmat with traditional slab foam with a 1.4 specific gravity barrier layer (e.g., TPO); (2) Optimized 1.8 specific gravity dashmat, i.e., a dashmat with traditional slab foam with a 1.8 specific gravity barrier layer (e.g., TPO); and (3) Optimized 1.4 specific gravity dashmat, i.e., a dashmat with Foamex 2 pcf viscoelastic foam with a 1.4 specific gravity barrier layer (e.g., TPO). It is noted that a seal wear issue was identified in 630 Hz for some tests (particularly those showing negative dB improvements).

[0075] FIG. 7 illustrates that the dashmat with the viscoelastic foam in accordance with the present invention performs better up to 2000 Hz as compared to traditional slab foam and similar to the traditional slab foam above 2000 Hz.

[0076] The use of viscoelastic foam as the sound-absorbing layer 12 increases the damping of vibration on the steel sheet metal to which the system 10 is applied. This reduces the noise radiation into the interior of the vehicle. The viscoelastic foam also reduces the vibration motion of the barrier layer 14 through damping. That is, the absorbing layer dampens vibrations to the barrier layer to reduce vibration of said barrier layer. In this manner, the absorbing layer also acts as a vibration-damping layer. This may result in an increase in transmission loss of the system 10. Further viscoelastic foams have good sound absorption properties due to the foam's cell structure and viscoelasticity. It will be appreciated that the viscoelastic foam layer is adapted to be placed against a substrate, such as the component of the vehicle.

[0077] FIG. 8 shows a damping comparison of various samples of foam of equal thickness. The first foam listed in the legend is a viscoelastic foam as set forth above but is 2 pcf foam. The second foam listed is a slab foam that is 1.2 pcf. The weight of the foam sample is also shown. The slab foam used comprises Melamine. The damping test was performed in a manner known in the art. The sample was excited with vibration. The transfer function is calculated by dividing the acceleration of the plate with the force applied. In this manner, the effect of the force magnitude on the results is eliminated. As can be seen in FIG. 8, the viscoelastic foam results in lower vibration levels by means of higher damping. Thus, when used in a system 10 as the sound-absorbing layer 12, the viscoelastic foam reduces the vibration motion of the barrier layer 14 through damping. This can increase the transmission loss of the overall system.

[0078] FIG. 9 shows a damping comparison of samples having equal mass. The test was performed in the same manner as set forth above in connection with FIG. 8.

[0079] FIG. 10 shows the effect on insertion loss by placing the viscoelastic layer against the steel. More specifically, one sample of a system 10 was prepared. The sample consisted of a viscoelastic foam absorbing layer 12, a HIPS barrier layer 14 and a shoddy absorbing layer 12. The tests were performed by first placing the shoddy absorber layer adjacent the steel and determining the insertion loss in the same manner as set forth above. Subsequently, the same sample was tested by placing the viscoelastic absorber layer against the steel and determining the insertion loss. The results are shown in FIG. 10. As can be seen, an increase in insertion loss is achieved when the viscoelastic foam is place against the steel. Thus, it is preferred that the viscoelastic foam layer be placed against the substrate, such as the vehicle component when the system 10 is installed.

[0080] FIG. 11 shows the effect of the damping of the viscoelastic foam on the barrier layer. In order to test the effect of damping by a viscoelastic-absorbing layer on the barrier, two samples were tested. In each case the absorbing layer was a viscoelastic foam. In the first sample, the viscoelastic foam is the FOAMEX foam identified above. In the second sample, the viscoelastic foam comprises Qylite, also available from FOAMEX. The barrier layer in each case was HIPS. Frequency response as shown in FIG. 11 means the same thing as the transfer function as shown in FIG. 8. The test to determine the frequency response was the same as set forth above in connection with FIG. 8. As can be seen from the results shown in FIG. 11, a viscoelastic foam absorber layer reduces the motion or vibration of the barrier layer. This results in less noise being transmitted to the interior of the vehicle.

[0081] It will also be appreciated that, while particularly well suited for automotive applications, the system 10 can also be used in other applications. Such other applications include construction, industrial, appliance, aerospace, truck/bus/rail, entertainment, marine and military applications.

[0082] Although the invention has been described in detail in the foregoing for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the claims.