JP2007519556A - Automotive dash insulator containing viscoelastic foam - Google Patents

Abstract

  A sound insulation system including a viscoelastic foam is described. The sound insulation system includes a sound absorbing layer. The sound absorbing layer can include a viscoelastic foam. An optional barrier layer is adjacent to the sound absorbing layer. In addition, an optional base layer is disposed adjacent to the sound absorbing layer and on the opposite side away from the optional barrier layer. This sound insulation system is particularly suitable for use as a vehicle dash mat.

Description

  This application claims benefit based on United States Provisional Application No. 60 / 535,933 (filing date 12 January 2004). The disclosure of that application is incorporated herein by reference.

  The present invention relates generally to sound insulation systems. More particularly, the present invention relates to a sound insulation system including a viscoelastic foam.

  Automakers have made efforts to reduce overall vehicle noise and vibration. Noise, vibration, and harshness, or “NVH” suppression, are important considerations in vehicle design. In the past, it was typical for almost all vehicle noise to be due to engine noise. It has become important to reduce other noise sources, such as tires, wind noise and exhaust, as well as engine noise. Recently, suppressing vehicle interior noise has been directly linked to consumer needs for vehicle noise reduction.

  Therefore, great efforts have been made to reduce vehicle interior noise. One approach is to use a barrier called a dash mat or dash insulator system. Use a dash mat to reduce noise from the engine to the car. Typically, a dash mat is placed against or adjacent to the base body to form a protective wall so that noise from the engine into the vehicle is reduced as it passes through the protective wall. A general description of dash mat technology is described in US Patent Application Publication 2003/0180500, the entire contents of which are expressly incorporated herein by reference.

  Typical conventional dash mats are typically decouplers (separators) made of foam (slabs or cast foam) and typically thermoplastic polyolefin (TPO) or ethylene vinyl acetate sheets (EVA). It is made with the barrier (barrier material) made of. This dash mat is intended to reduce the noise of the engine compartment as a whole. Such barrier-type dash mats are typically relatively heavy to provide the desired noise reduction effect.

  A substantial part of the performance of the dash mat is believed to depend on the nature of the foam. In general, the performance of a foam is considered to vary depending on the transmission loss, sound absorption, elastic coefficient, and damping characteristics of the foam.

  More recently, lightweight dash mats have been used. In order to reduce weight, a sound-absorbing material such as shoddy cotton is used. This type of dash mat is not intended to block engine noise, but is intended to absorb and dissipate engine noise as it travels from the engine compartment into the vehicle. This lightweight dash mat also reduces the overall weight of the vehicle. A general description of this type of lightweight dash mat is described in US Pat. Nos. 6,145,617 and 6,296,075, the entire contents of which are incorporated herein by reference.

  The main function of both types of dash mats is to reduce the noise level in the car. Traditionally, blocking noise in accordance with the law of mass action has been considered the best means for noise transmission loss and noise reduction. Transmission loss and noise reduction are used as measured parameters to evaluate dash mat performance.

  Conventional dash mats have been somewhat successful in reducing vehicle noise, but are not yet fully satisfactory. That is, the sound insulation foam (that is, the decoupler) was not effective in that it did not have proper acoustic absorption characteristics. In addition, the conventional sound insulation foam has a small noise prevention effect due to vibration of the base or the barrier layer.

  Therefore, a dash with enhanced transmission loss performance characteristics to reduce both the noise of the engine compartment that passes through the defensive wall and the noise that enters into the vehicle from other noise sources while the vehicle is operating. It is desirable if a mat is provided.

  According to a first embodiment of the present invention, the sound absorbing layer has an absorption coefficient in the range of about 0.2 to about 1.0 and an attenuation loss coefficient in the range of about 0.3 to about 2.0. A sound insulation system is provided.

  According to another embodiment of the present invention, a sound absorbing layer having an absorption coefficient in the range of about 0.2 to about 1.0 and an attenuation loss coefficient in the range of about 0.3 to about 2.0. A sound insulation system is provided. The system further includes a barrier layer connected to the viscoelastic foam and substantially impermeable to fluid flow.

  According to another embodiment of the present invention, a sound insulation system including a sound absorbing layer including a viscoelastic foam is provided. The viscoelastic foam has an absorption coefficient in the range of about 0.7 to about 1 and a damping loss coefficient in the range of about 0.4 to about 1.6 within a frequency range of about 1000 Hz to about 6000 Hz. Is within. The system further includes a barrier layer connected to the viscoelastic foam and substantially impermeable to fluid flow.

  The preferred embodiments described below are merely exemplary and are not intended to limit the invention, its application, or its use.

  FIG. 1 is a cross-sectional view of one embodiment of the present invention. As shown in FIG. 1, the entire sound insulation system is indicated by 10. The sound insulation system 10 desirably includes a multilayer structure. The sound insulation system 10 preferably includes a sound absorbing layer, generally designated 12. An optional barrier layer, generally indicated at 14, is preferably adjacent to the sound absorbing layer 12. As shown in FIG. 1A, it is desirable that the system 10 be attached to any substrate, generally indicated at 14, with fasteners or other means, either in a removable or permanently secured state. The substrate 16 is preferably adjacent to the sound absorbing layer 12 and on the opposite side away from the barrier layer 14.

  The system 10 desirably provides a multi-layer dash mat that is preferably used to reduce noise transmission into the vehicle through the entire dash panel. In addition to sound insulation, it is desirable for the system 10 to reduce the noise level in the vehicle by absorbing sound. In addition, it is desirable to be able to use the system 10 in the engine compartment to reduce the noise generated from the engine compartment and reaching the exterior of the vehicle. The system 10 further enhances the sound quality perception of the interior and exterior environment. The system 10 also includes liners such as wheel wells, fenders, engine compartments, door panels, roofs (eg, headliners), floor body treatments (eg, carpet backing), trunks, and packaging shelves (eg, package tray liners). It can also be incorporated into other automotive parts such as, but is not limited to these liners. Furthermore, the system 10 can be incorporated in applications other than automobiles.

  The sound absorbing layer 12 desirably includes a foam material 18. The foam material 18 preferably comprises a viscoelastic foam, more desirably a viscoelastic flexible foam, and even more desirably a viscoelastic flexible polyurethane foam. Viscoelastic foams, also called memory foams (memory foams) or temper foams (temper foams), are generally characterized by the fact that the foam cells are almost open and the recovery after compression is slow It is.

  The present invention uses viscoelastic foams in the dash mat system, which can also be used as an alternative to vibration damping materials commonly referred to as mastic trees.

  Viscoelastic foams are desirable for the practice of the present invention, but other foams having the required properties described herein can be used alone or in combination. That is, the foam material 18 may be a natural material or a synthetic material, and may be a slab or a molded body. The foam material 18 may be a foam cell that is open, closed, or a combination of both. The foam material 18 may include latex foamed polyolefin, polyurethane, polystyrene, polyester, and combinations thereof. The foam material 18 may be a recycled foam material, a foam-impregnated mat, or a microcell elastomer foam material. The foam material 18 may include organic and / or inorganic fillers. Further, other additives that can be contained in the foamed material 18 include flame retardants, antifogging agents, ultraviolet absorbers, heat stabilizers, pigments, colorants, malodor prevention agents, etc. Not limited.

  According to a preferred embodiment of the present invention, the foam material 18 has a relatively high absorption coefficient. Regardless of the particular theory of operation of the present invention, it is believed that the relatively high absorption coefficient increases the overall transmission loss due to sound dissipation in the foam material 18.

FIG. 2 shows the sound absorption of various foams. VE refers to a viscoelastic foam. PCF is a measure of density and the unit is lb / ft ³ . The VE foam used is FOAMEX H300-10N. The slab foam was melamine and the cast foam was a polyurethane foam. According to a preferred embodiment of the present invention, the absorption coefficient of the foam material 18 is desirably about 0.2 or greater, more desirably about 0.4 or greater, even more desirably about 0.7 or greater, and most desirably about 1. 0. In the most preferred embodiment, the absorption coefficient is in the range of about 0.7 to 1 at a frequency in the range of about 1000 Hz to about 6000 Hz.

  According to a preferred embodiment of the present invention, the foam material 18 has a relatively low elastic modulus. Without relying on a specific theory for the operation of the present invention, the relatively low modulus of elasticity allows the foamed material 18 to more uniformly contact the substrate 16 (e.g., a barrier wall or vehicle steel structure), thus causing flanking noise. ) Is considered to be prevented from entering the car. Thus, it is desirable that the elastic modulus is relatively low. When the elastic modulus is low, the foam material 18 is easily adapted to the substrate. If the elastic modulus is too high, the foam material 18 is too rigid to easily fit into the substrate. However, the elastic modulus should not be so low that structural stability cannot be ensured.

In general, a very low elastic modulus is sufficient to maintain the foam cell structure. According to a preferred embodiment of the present invention, the elastic modulus of the foam material 18 is in the range of about 4 × 10 ³ Pa to about 1 × 10 ⁶ Pa.

In another desirable embodiment, the elastic modulus is in the range of about 1 × 10 ⁴ Pa to about 1 × 10 ⁵ Pa. Each of these ranges is measured with the test apparatus shown in FIG.

  According to a preferred embodiment of the present invention, the foam material 18 has a relatively high damping loss factor (tan δ). Regardless of the specific theory of the operation of the present invention, it is considered that the transmission loss of the entire dash mat increases because the vibration of the vehicle steel structure is reduced by the relatively high damping loss coefficient. According to a preferred embodiment of the present invention, the foaming material 18 has a damping loss factor (tan δ) of about 0.3 or greater, more desirably about 0.4 or greater, and even more desirably 1.0 or greater.

  According to another preferred embodiment of the present invention, the damping loss factor (tan δ) of the foam material 18 is 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 more desirably within the range of about 0.4 to about 1.6. Each of these values is measured with the test apparatus shown in FIG.

  To list non-limiting examples, foam materials satisfying the above requirements are Dow's experimental viscoelastic polyurethane foams # 76-06HW, # 76-16-08HW, # 76-16-10HW, # 56. -53-01HW and # 56-53-29HW; Foamax 2 lb / cu.ft. And Foamax H300-10N 3% viscoelastic foam (commercial product); Carpenter's 2.5% viscoelastic foam (commercial product); and There are 25010MF and 30010MF (commercially available), which are viscoelastic foams of Leggett & Platt.

  The thickness of the sound absorbing layer 12 can be changed according to the application. This thickness is desirably from about 6 mm to about 100 mm, more desirably from about 12 mm to about 25 mm, but may be outside these ranges depending on the particular application. The thickness affects the rigidity of the sound absorbing layer 12. The thickness of the sound absorbing layer 12 may vary or may be non-uniform.

  Furthermore, the sound absorbing layer 12 may include a combination of a plurality of materials adjacent to each other. That is, the sound absorbing layer 12 may include two or more sublayers made of the same or different materials.

  The normal incident sound absorption coefficient of various sound absorbing layers was measured according to ASTM E1050. FIG. 2 shows normal incident sound absorption profiles for Dow # 76-16-10HW and # 76-16-08HW and Leggett & Platt 30010MF as three types of sample foams. All of these three types of sample foams are within a desirable sound absorption range in the range of 1000 to 8000 Hz.

  The elastic coefficient and damping property of the sound absorbing layer of the present invention were measured using a plate, a vibrator, and two accelerometers. FIG. 3 schematically shows the test apparatus. The transmissibility between the accelerometer 1 and the accelerometer 2 was measured, and the primary resonance frequency of this system was determined. Next, the elastic modulus was determined by the following equation.

E = ω ² mt / WL
Where E = elastic coefficient (Pa)
ω = angular frequency (rad / s)
m = plate mass (kg)
t = foam thickness (m)
W = width of plate (m)
L = length of plate (m)
The attenuation rate was obtained from the transmission rate by the half-width method.

  The barrier layer 14 preferably includes a relatively thin and substantially impermeable layer. Barrier layer 14 is substantially impermeable to fluid flow. According to a preferred embodiment of the present invention, the barrier layer 14 comprises a thermoplastic olefin. As a non-limiting example, the barrier layer 14 is made of acrylonitrile-butadiene-styrene, impact polystyrene, polyethylene terephthalate, polyethylene, polypropylene (eg, filled polypropylene), polyurethane (eg, molded polyurethane), ethylene vinyl. It is desirable to include a sheet of acetate or the like. It is also desirable that the barrier layer 14 has good moldability and shape retention and can be adapted to the sound absorbing layer 12 and / or the substrate 16 for each application. Moreover, the barrier layer 14 may contain an organic and / or inorganic filler. Further, other additives that can be contained in the barrier layer 14 include flame retardants, anti-fogging agents, ultraviolet absorbers, heat stabilizers, pigments, colorants, malodor prevention agents, etc. Not limited.

  According to a preferred embodiment of the present invention, the barrier layer 14 comprises about 15 wt% polypropylene, about 25 wt% thermoplastic elastomer (eg, Kraton®, commercial product), about 55 wt% calcium carbonate loading. And about 5 wt% additive (eg processing aids, colorants, etc.).

According to a preferred embodiment of the present invention, the specific gravity of the barrier layer 14 is desirably about 0.9 or greater, more desirably about 1.4 or greater, and even more desirably about 1.6 or greater. The barrier layer 14 preferably has a weight per surface area of about 0.1 kg / m ² or more. More desirably, the weight per surface area of the barrier layer 14 is greater than 0.4 kg / m ² .

  Similar to the sound absorbing layer 12, the thickness of the barrier layer 14 may also vary. Desirably, the thickness of the barrier layer 14 is 0.1 to about 50 mm. Again, this thickness may vary beyond the desired range depending on the particular application, and of course the thickness may be non-uniform.

  Although a single barrier layer 14 is illustrated, it is needless to say that a plurality of barrier layers 14 having different thicknesses may be used. That is, the barrier layer 14 may include two or more sublayers made of the same or different materials.

  As described above, the barrier layer 14 desirably has good formability and shape retention to adapt the system 10 to the substrate 16 for each application. Any suitable fabrication technique may be used to combine the sound absorbing layer 12 and the barrier layer 14. As an example, various layers can be connected to each other by a heat lamination method or by applying an adhesive between layers. The above adhesive may be thermally activated. Alternatively, the various layers can be joined together by heating during the molding process of the laminated layers and then pressing the molding tool or pressing the molding tool after applying an adhesive.

  The system 10 can be made with a cast foam tool, i.e., the material of the barrier layer 14 (such as a polymer film) is placed in the center of the mold and then the foam (such as a viscoelastic polyurethane foam material) is loaded. It can be produced by injecting into both sides of the tool. As another method of making the system 10, the sound absorbing layer 12 and the barrier layer 14 are made together and / or separately and then conventional methods such as mechanical fastening, heat melting, sonic melting, and / or bonding ( For example, an adhesive or a tape is used to fix the two.

  The substrate 16 may be composed of any number of suitable materials. By way of non-limiting example, the substrate 16 may be comprised of metal, natural fiber mat, synthetic fiber mat, shoddy pad, flexible polyurethane foam material, rigid polyurethane foam material, and combinations thereof.

  With respect to the method of attaching the sound absorbing layer 12 to the base 16 with a fastener or the like, any number of appropriate methods may be applied. By way of non-limiting example, mechanical fasteners, heat melting, sonic melting, and / or bonding (eg, adhesives, tapes, etc.) can be used.

  An analysis was conducted to clearly show the performance advantage of using the viscoelastic foam of the present invention for the dash mat as compared with the case of using a conventional lightweight slab foam. The dash mat performance was determined by testing the transmission loss of a system consisting of a 0.8 mm steel panel and a dash mat system (ie, a viscoelastic foam sound absorbing layer and a thermoplastic olefin barrier layer). The transmission loss was calculated by a simulation method called statistical energy analysis. This analysis method utilizes the material properties of the foam and other materials to calculate transmission losses and other quantities within the frequency range of 100-10000 Hz.

  The set variables used in this analysis are: (1) foam type (a) conventional lightweight slab foam, (b) Dow viscoelastic foam (model # 76-16-10HW), and (c) Foamax 2% viscoelastic foam, (2) 1.2, 1.4, and 1.6 were used as the specific gravity of the barrier layer (eg, thermoplastic olefin), and (3) 13 mm and 18 mm were used as the thickness of the foam. . The barrier layer thickness was constant at 2.4 mm.

  The dash mat structure simulated the typical sound absorbing / barrier layer system outlined in FIG. 1A. The transmission loss was calculated for each combination of the above set variables.

  FIG. 4 shows a comparison between structures using various foam types and barrier layers of various specific gravities for a foam thickness of 18 mm. The test method is described below. As shown in FIG. 4, when the foam type is changed to any one of the viscoelastic foams, the transmission loss of the dash mat system is increased particularly in the region of 1000 to 10000 Hz. Further, when the foam type is changed to any one of the viscoelastic foams, the transmission loss becomes larger than when the specific gravity of the barrier layer is increased while the slab foam is used.

  In order to more effectively compare the set variables, a reference structure was selected. As a reference structure, a structure in which a barrier layer having a specific gravity of 1.4 was combined with a conventional slab foam of 18 mm was selected. All other viscoelastic structures were compared to the performance of this reference structure.

  The sample was placed on 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 from the speakers in the reverberation room, and the sound pressure level was measured with four microphones arranged at a distance of 1.17 m from the steel plate. Twelve microphones were arranged in a semi-anechoic chamber at a distance of 0.76 m from the outer foam side of the sample. The noise reduction rate was calculated using Equation 1 in accordance with the general rules of SAE J1400. The result of the noise reduction test is shown in FIG.

Formula 1 NR = (average SPL1) − (average SPL2)
Here, average SPL2 = anechoic sound pressure level (dB)
Average SPL1 = Reverberation sound pressure level (dB)
The weight per surface area for all structures using viscoelastic foam is shown compared to the weight per surface area. The relative weight of the individual structures was compared using the weight per surface area (ie, the mass of the dash mat structure divided by the panel area). The weight of the dash mat structure is preferably small in order to improve vehicle fuel costs, engine performance, and the like. Of the structures using viscoelastic foam, the weight per surface area of three is smaller than the standard. These are (1) 13 mm Dow viscoelastic foam (model # 76-16-10HW) with a specific gravity of 1.2, (2) 18 mm Foamex 2% viscoelastic foam, and (3) 13 mm Foamex 2% viscoelastic foam It is.

  FIG. 6 shows two types of structures using viscoelastic foam in comparison with the reference structure. It has been demonstrated that viscoelastic foams increase dash mat transmission loss with equal or lower weight.

  A dash section of a GM truck vehicle was also tested, and the noise reduction capability of the viscoelastic foam was determined by comparison with a conventional slab foam dash mat. Since it is difficult to measure transmission loss for vehicle sections, noise reduction was measured instead of transmission loss. A vehicle section was placed in the wall between the reverberation room and the anechoic room. The sound pressure level is measured in both rooms, and the noise reduction rate is calculated.

  FIG. 7 shows the result of testing the dash section of the vehicle using three types of dash mats. The three types of dash mats tested were: (1) an optimized dash mat with a specific gravity of 1.4, ie a dash mat combining a conventional slab foam with a barrier layer (eg TPO) with a specific gravity of 1.4, (2) An optimized dash mat with a specific gravity of 1.8, i.e. a dash mat with a conventional slab foam combined with a barrier layer with a specific gravity of 1.8 (e.g. TPO), (3) an optimized dash mat with a specific gravity of 1.4, i.e. It is a dash mat in which a barrier layer (for example, TPO) having a specific gravity of 1.4 is combined with Foamex 2% viscoelastic foam. In some tests, a seal wear phenomenon was observed at 630 Hz (particularly, a test result in which the dB reduction rate was negative).

  As shown in FIG. 7, the performance of the dash mat using the viscoelastic foam of the present invention is better than the conventional slab foam up to 2000 Hz, and is equal to the conventional slab foam above 2000 Hz.

  By using the viscoelastic foam as the sound absorbing layer 12, the vibration damping of the steel sheet equipped with the system 10 is increased. As a result, noise emission into the vehicle is reduced. Oscillating motion of the barrier layer 14 is also reduced by the damping action of the viscoelastic foam. That is, the sound absorbing layer attenuates the vibration transmitted to the barrier layer, thereby reducing the vibration of the barrier layer. In this way, the sound absorbing layer also acts as a vibration damping layer. This can increase the transmission loss of the system 10. Further, the viscoelastic foam has excellent sound absorption characteristics due to the cell structure and viscoelasticity of the foam. The viscoelastic foam layer is preferably adjusted so as to be in contact with a substrate such as a vehicle member.

  FIG. 8 shows a comparison of attenuation for various samples using foams of equal thickness. The foam shown at the top of the legend is the viscoelastic foam described above, but 2% foam. The second foam is a slab foam, 1.2%. The weight of each foam sample is also shown. The slab foam used contains melamine. The attenuation test was performed by a conventionally known method. Vibration was applied to the sample. The transfer function was calculated by dividing the plate acceleration by the load external force. In this way, the influence of the magnitude of the external force on the result was eliminated. As shown in FIG. 8, the viscoelastic foam lowered the vibration level by a high damping action. Thus, when a viscoelastic foam is used as the sound absorbing layer 12 of the system 10, the vibrational motion of the barrier layer 14 is reduced by the damping action. This increases transmission loss as a whole system.

  FIG. 9 shows a comparison of attenuation between samples of equal mass. The test was performed in the same way as described in connection with FIG.

  FIG. 10 shows the effect on insertion loss due to the arrangement of the viscoelastic layer in contact with steel. More specifically, one sample of system 10 was made. This sample was composed of a viscoelastic foam sound absorbing layer 12, a HIPS barrier layer 14, and a shody sound absorbing layer 12. In the test, first, the shody sound absorbing layer was placed in contact with the steel, and the insertion loss was determined by the same method as described above. Subsequently, the insertion loss was calculated | required by arrange | positioning a viscoelastic sound-absorbing layer in contact with steel with the same sample. The results are shown in FIG. As shown in the figure, the insertion loss was increased by placing the viscoelastic foam in contact with the steel. Thus, when the system 10 is mounted on a base such as a vehicle member, it is desirable to place the viscoelastic foam layer in contact with the base.

  FIG. 11 shows the influence on the barrier layer due to the attenuation of the viscoelastic foam. Two samples were tested to test the effect on the barrier layer by the attenuation of the viscoelastic sound absorbing layer. In both cases, the sound absorbing layer was a viscoelastic foam. The viscoelastic foam of the first sample was the above-mentioned FOAMEX foam. The second sample viscoelastic foam is Qylite, also available from FOAMEX. In both samples, the barrier layer was HIPS. The frequency response in FIG. 11 means the same as the transfer function in FIG. The test for determining the frequency response is the same as described above with respect to FIG. As can be seen from the results shown in FIG. 11, the viscoelastic foam sound absorbing layer reduces the movement or vibration of the barrier layer. As a result, noise transmitted into the vehicle is reduced.

  System 10 is particularly suitable for automotive applications, but can also be used for other applications. Other applications include construction, industry, machinery, aviation, truck / bus / railway, entertainment, marine and military applications.

  While the invention has been described in detail for purposes of illustration, the details are for purposes of illustration only and may be modified by one skilled in the art without departing from the spirit and scope of the invention within the scope of the claims. is there.

1 is a schematic cross-sectional view of a sound insulation system according to the general teachings of the present invention. It is sectional drawing which shows the state which attached the sound insulation system shown in FIG. 1 to the base | substrate by one Embodiment of this invention. It is a graph which compares the normal incidence sound absorption coefficient of the various sample sound absorption layers by one Embodiment of this invention. It is a schematic diagram which shows the test layer for calculating | requiring the elastic modulus and attenuation factor of various sample sound absorption layers by one Embodiment of this invention. It is a graph which compares and shows the transmission loss characteristic of the sound insulation system of this invention, and the conventional sound insulation system. It is a graph which compares and shows the weight per surface of the sound insulation system of this invention, and the conventional sound insulation system. 6 is a graph showing transmission loss of the sound insulation system of the present invention and the conventional sound insulation system in comparison with a preset reference profile according to an embodiment of the present invention. It is a graph which compares and compares the average noise reduction rate of the sound insulation system of this invention, and the conventional sound insulation system by decibel improvement by one Embodiment of this invention. It is a graph which shows an attenuation test result. It is a graph which shows an attenuation test result. It is a graph which shows an insertion loss test result. It is a graph which shows an attenuation test result.

Claims (19)

  A sound insulation system including a sound absorbing layer having an absorption coefficient in the range of about 0.2 to about 1.0 and an attenuation loss coefficient in the range of about 0.3 to about 2.0.   The sound insulation system according to claim 1, wherein the sound absorbing layer includes a viscoelastic foam.   The sound insulation system of claim 2, wherein the viscoelastic foam has a damping loss factor in the range of about 0.4 to 1.6. The sound insulation system according to claim ^3, wherein the elastic modulus of the viscoelastic foam is in a range of about 4 × 10 ³ Pa to about 1 × 10 ⁶ Pa.   The sound insulation system according to claim 4, further comprising a barrier layer fixed to the viscoelastic foam, the barrier layer being substantially impermeable to fluid flow.   6. The sound insulation system of claim 5, wherein the absorption coefficient of the viscoelastic foam is desirably in the range of about 0.7 to about 1 within a frequency range of about 1000 Hz to about 6000 Hz.   The sound insulation system according to claim 6, further comprising a base, wherein the viscoelastic foam is fixed to the base.   The sound insulation system according to claim 7, wherein the base is a metal structure on a vehicle. A sound absorbing layer having an absorption coefficient in the range of about 0.2 to about 1.0 and an attenuation loss coefficient in the range of about 0.3 to about 2.0, and connected to the sound absorbing layer, A sound insulation system including a barrier layer that does not allow fluid flow to permeate.   The sound insulation system according to claim 1, wherein the sound absorbing layer includes a viscoelastic foam.   The sound insulation system of claim 10, wherein the damping loss factor of the viscoelastic foam is in the range of about 0.4 to 1.6. The sound insulation system of claim 11, wherein the elastic modulus of the viscoelastic foam is in the range of about 4 × 10 ³ Pa to about 1 × 10 ⁶ Pa.   The sound insulation system of claim 12, wherein the absorption coefficient of the viscoelastic foam is desirably in the range of about 0.7 to about 1 within a frequency range of about 1000 Hz to about 6000 Hz.   The sound insulation system according to claim 13, further comprising a base, wherein the viscoelastic foam is fixed to the base.   The sound insulation system according to claim 14, wherein the base body is a metal structure on a vehicle. Viscoelastic foam having an absorption coefficient in the range of about 1000 Hz to about 6000 Hz in the range of about 0.7 to about 1 and an attenuation loss coefficient in the range of about 0.4 to about 1.6 And a sound insulation system comprising a barrier layer connected to the viscoelastic foam and substantially impermeable to fluid flow. The sound insulation system according to claim 16, wherein the elastic modulus of the viscoelastic foam is in the range of about 4 × 10 ³ Pa to about 1 × 10 ⁶ Pa.   The sound insulation system according to claim 17, further comprising a base, wherein the viscoelastic foam is fixed to the base. The sound insulation system according to claim 18, wherein the base body is a metal structure on a vehicle.

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