Patent Publication Number: US-2006013417-A1

Title: Acoustical panel assembly

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
      This application claims the benefit of U.S. Provisional Application No. 60/588,872, filed Jul. 16, 2004, which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The invention relates in general to an acoustical panel assembly, and in particular to an acoustical panel assembly comprising a panel made of a material formed by a reaction injection molding (RIM) process, a reinforced reaction injection molding (RRIM) process, or a structural reaction injection molding (SRIM) process with an acoustic device, such as a loudspeaker, an exciter, a piezoelectric transducer, and the like, mounted thereon.  
      2. Description of the Related Art  
      Traditionally, auto manufacturers have made sole use of traditional cone speakers that have a minimum depth requirement that has demanded a minimum packaging space. This requirement has ensured that audio speaker placement has often been determined not by optimum in-car sound quality, but by available space. Thus, most vehicles audio speakers are tucked away down by the occupants&#39; knees and not necessarily located for optimum listening.  
      An acoustic device, such as a piezoelectric transducer, an electrodynamic device, a flat panel loudspeaker, distributed mode loudspeaker (DML), and the like, applies bending wave energy to a panel to cause the panel to resonate and produce an acoustic output (i.e., sound). One such acoustic device is commercially available from New Transducers Limited (NXT™) of Huntingdon, England. A typical electrodynamic device, for example, comprises a magnet assembly rigidly fixed to a housing to define an annular gap, and a voice coil and coil former assembly disposed in the annular gap and rigidly fixed to the panel near to the geometric center thereof.  
      Typically, the acoustic device is mounted to the panel by using a separate mounting member, such as a mounting plate, that is fixedly attached to the panel using one or more fasteners, such as screws, adhesives, double-side tape, or the like. After the separate mounting member is fixedly attached to the panel, the acoustic device can be fixedly attached to the panel via the mounting member.  
      It has been found that a suitable conventional material for the panel that will produce an acceptable frequency response is made of an extremely low-density, rigid plastic foam material commercially available under the tradename ROHACELL® sold by Roehm GMBH Limited located in the Fed. Rep. of Germany. ROHACELL® is a polymethacrylimide (PMI) hard foam, that is used as a core material for sandwich constructions. For example, ROHACELL® is typically used as a modeling material for architects and sculptors, and in some cases, as a building insulation. ROHACELL® is available with densities ranging from  2 . 0  to  6 . 87  lbs/ft 3  ( 32  to  110  kg/m 3 ). However, such a material may not have the necessary structural properties, such as stiffness, rigidity, and the like, that is suitable for use in most home, office and/or automotive applications, such as for use in vehicular door panels, instrument panels, trim panels, residential and commercial floor and ceiling panels, and the like.  
     SUMMARY OF THE INVENTION  
      The inventors of the present invention have recognized these and other problems associated with conventional materials used for panels that resonate and produce an acoustic output, while providing the structural characteristics that are suitable for automotive applications. To this end, the inventors have developed a material for use as a panel made of a material formed by a Reaction Injection Molding (RIM) process, a Reinforced Reaction Injection Molding (RRIM) process, or a Structural Reaction Injection Molding (SRIM) process that can widely be used in automotive applications, and unexpectedly produces an acceptable acoustic output when the acoustic device is mounted thereon.  
      In an embodiment of the invention, an acoustical panel assembly comprises a panel having a core made of synthetic material comprising a mixture of isocynate and polyol, and an acoustic device mounted to an exterior surface of the panel.  
      In another embodiment of the invention, an acoustical panel assembly comprises a core made of a synthetic material having a specific gravity in a range between about 0.1 and 1.4, and an acoustic device mounted to an exterior surface of the core.  
      In a method of the invention, the method comprises the steps of forming a panel comprising a core made of a synthetic material by one of a reaction injection molding (RIM) process, a reinforced reaction injection molding (RRIM) process, and a structural reaction molding (SRIM) process, and mounting an acoustic device to the panel. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      In the drawings:  
       FIG. 1  shows a front perspective view of an acoustical panel assembly comprising a panel comprising a core with an acoustic device mounted on an exterior surface of the panel according to an embodiment of the invention;  
       FIG. 2  is a cross-sectional view of the panel comprising a core having reinforcing fibers taken along line  2 - 2  of  FIG. 1 ;  
       FIG. 3  is a cross-sectional view of the panel comprising a core having a fiberglass mat embedded therein taken along line  2 - 2  of  FIG. 1 ;  
       FIG. 4  is a cross-sectional view of the panel comprising a core and a scrim material on one exterior surface of the core taken along line  2 - 2  of  FIG. 1 ;  
       FIG. 5  is a cross-sectional view of the panel comprising a core and a cover material and a layer of foam between the cover material and the core taken long line  2 - 2  of  FIG. 1 ;  
       FIG. 6  shows a side view of the acoustical panel assembly of  FIG. 1  with an integrally formed attachment member and acoustical device mounted to the panel;  
       FIG. 7  shows perspective view of the inner surface of the acoustical panel assembly of  FIG. 6 ;  
       FIG. 8  shows a partial side view of the acoustical panel assembly with an attachment member integrally formed therewith according to another embodiment of the invention;  
       FIG. 9  is a flow chart diagram illustrating a method of manufacturing the panel according to one embodiment of the invention;  
       FIG. 10  is a graph of the frequency response for a 30 cm square RIM panel without any reinforcement and having a thickness of approximately 10 mm when the acoustic device is mounted at a location directly at the center of the panel; and  
       FIG. 11  is a graph of the frequency response for a 30 cm square conventional ROHACELL® panel having a thickness of approximately 10 mm when the acoustic device is mounted at a location directly at the center of the panel. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
      Referring to  FIGS. 1-4 , an acoustical panel assembly  10  includes a panel  12 . For automotive applications, for example, the panel  12  may be in the form of a vehicular headliner, door panel, valence panel, dashboard, package tray, or the like. For residential and commercial applications, the panel  12  may be in the form of floor or ceiling panel. For example, the panel  12  may form a door panel in which one exterior surface forms a Class “B” surface that faces away from the interior of the vehicle and is not visible to the occupants, and the opposed exterior surface forms a Class “A” surface that faces the interior of the vehicle and is visible to the occupants.  
      As shown in  FIG. 1 , one embodiment of the acoustical panel assembly  10  includes the panel  12  comprising a core  13  made of a synthetic material of unitary construction having an inner surface  14  and an outer surface  16 . The synthetic material may comprise, for example, a mixture of isocynate and polyol by using a RIM process to form the core  13  of the panel  12 . However, it will be appreciated that a single, unmixed composition of synthetic material or other mixtures of synthetic materials are within the scope of the invention. In an embodiment in which the synthetic material comprises a mixture of isocynate and polyol in which the ratio of isocynate to polyol is approximately equal to  1 . 62 : 1 . However, it will be appreciated that other mixture ratios of isocynate and polyol are within the scope of the invention.  
      As illustrated in  FIG. 2 , the panel  12  may also include a reinforcing material encapsulated within the core  13  by using a RRIM process to form the panel  12 . The reinforcing material may be any suitable reinforcing material known to those skilled in the art. For example, the reinforcing material may be in the form of reinforcing fibers  18 , such as glass fibers, carbon fibers, or the like. The reinforcing fibers  18  may alternatively include natural fibers, such as, for example, hemp fibers, coconut fibers, kanuf fibers, flax fibers, or the like. As illustrated in  FIG. 3 , the reinforcing material may be in the form of a fiberglass mat  15  encapsulated within the core  13 , rather than the reinforcing fibers by using a RRIM process to form the panel  12 .  
      It will be appreciated that the invention can be practiced without the use of the reinforcement material encapsulated in the core  13  of the panel  12 . For example, as illustrated in  FIG. 4 , the core  13  does not include the reinforcing material  18  encapsulated therein, but rather a layer of reinforcing scrim material  19  may be bonded to the inner surface  14  of the core  13 . The scrim material  19  can also be bonded to the outer surface  16 , or both the inner surface  14  and the outer surface  16  of the core  13 . The scrim material  19  may comprise a “combo mat” that includes glass fibers, carbon fibers, or the like, and/or natural fibers, such as, for example, hemp fibers, coconut fibers, kanuf fibers, flax fibers, or the like. The “combo mat” may also include an adhesive material for bonding the “combo mat” to the core  13 . The embodiment of the panel  12  having the scrim material  19  on only one exterior surface of the core  13  may by useful in application in which the panel  12  needs a non-planar or curved profile.  
      As illustrated in  FIG. 5 , another embodiment of the panel  12  may include a cover  20  bonded to the outer surface  16  of the core  13  to form a decorative “A” surface of the panel  12 . The cover  20  may comprise any desirable material, such as, for example, vinyl, acrylic, thermoplastic olefin (TPO), polyethylene terepthalate (PET), cross-linked polyolefin (XLPO), or the like. Alternatively, the cover  20  may comprise a decorative cloth material, or the like. The cover  20  may be bonded or attached to the outer surface  16  of the core  13  by use of an adhesive (not shown), or other suitable means for bonding or attaching the cover  20  to the outer surface  16 . If desired, a layer  21  of foam material may be disposed between the cover  20  and the outer surface  16  of the core  13 . If desired, the cover  20  may have an embossed appearance for displaying, for example, a manufacturer&#39;s logo, or the like. As illustrated, the panel  12  does not include the reinforcing fibers  18  and/or the scrim material  19 . However, if desired, the reinforcing material  18  and/or the scrim material  19 , as shown in  FIGS. 2 and 3 , may be included in this embodiment of the panel  12 .  
      It will be appreciated that the panel  12  may comprise any combination of the various layers of materials stated above. For example, the synthetic panel  12  may include a layer of scrim material  19  in the form of a “combo mat” on both the inner and outer surfaces  14 ,  16  and a cover material  20  bonded to the scrim material  19  on the outer surface  16  to provide a decorative appearance. The cover material  20  may have an embossed appearance, if desired. In another example, the synthetic panel  12  may include the cover material  20  bonded to the outer surface  16  of the core  13  having a fiberglass mat  15  encapsulated therein. Other combinations of layers of materials are within the scope of the invention.  
      Referring now to  FIGS. 6 and 7 , the acoustical panel assembly  10  may include an attachment member  24  for attaching an acoustic device  26 , such as a loudspeaker, an exciter, a piezoelectric transducer, or the like, to the acoustical panel assembly  10 . One aspect of the invention is that the attachment member  24  is integrally formed with the panel  12  using known molding techniques, such as injection molding, or the like. For example, the attachment member  24  can be integrally formed with the panel  12  by using slides in a mold tool (not shown) that forms the panel  12 . Preferably, the attachment member  24  is integrally formed with the panel  12  at a location of the panel  12  that has a substantially flat topography to accommodate the substantially flat profile of the acoustic device  26 . However, the invention is not limited by the location at which the acoustic device  26  is mounted to the panel  12 . Because the attachment member  24  is integrally formed with the panel  12 , the inner and outer surfaces  14 ,  16  can be generally continuous, unlike conventional mounting systems in which an opening may be necessary for mounting a conventional acoustic device, such as a cone speaker.  
      In the illustrated embodiment, the attachment member  24  includes a pair of opposing, substantially identical mounting portions  28 . Each mounting portion  28  is generally L-shaped in cross section having a lower mounting portion  30  and an upper mounting portion  32  that generally conform to shape of the outer surface of the acoustic device  26 . To install the acoustic device  26  to the panel  12 , the acoustic device  26  is aligned with the attachment member  24  such that the lower mounting portion  30  and the upper mounting portion  32  are aligned with the acoustic device  26 . As the acoustic device  26  is moved toward the attachment member  24 , the lower mounting portion  30  and the upper mounting portion  32  flex slightly outward to allow the acoustic device  26  to be inserted into the attachment member  24 . Once the acoustic device  26  is fully inserted within the attachment member  24 , the lower mounting portion  30  and the upper mounting portion  32  flex inwardly and press against the acoustic device  24  to positively secure the acoustic device  24  against the inner surface  14  of the panel  12 .  
      It will be appreciated that the integrally formed attachment member  24  does not require a separate mounting plate for mounting the acoustic device  26  to the panel  12 , unlike conventional mounting devices, thereby eliminating the need for holes in the panel  12  for attaching the separate mounting plate to the panel. Thus, the integrally formed attachment member  24  provides a more aesthetic Class “A” surface than conventional attachment members.  
      In addition, it will be appreciated that the invention is not limited by the type of attachment member that is integrally formed with the panel  12 . For example, an attachment member  24 ′ may comprise a single piece of plastic material having a base portion  42  and an attachment portion  44  having a plurality of threads  46 , as shown in  FIG. 8 . The attachment member  24 ′ can be integrally formed with the panel  12  by placing the base portion  42  onto the mold tool prior to injecting the synthetic material into the mold tool. During the injection process, the synthetic material encapsulates the base portion  42 , while leaving the attachment portion  44  accessible for mounting the acoustic device  26 . The acoustic device  26  can be mounted to the attachment portion  44  by threading the acoustic device  26  onto the attachment portion  44 .  
      It will be appreciated that it is possible to mount the acoustic device  26  directly to the panel  12  without the need for the attachment member  24 ,  24 ′ by using an adhesive, or the like.  
      Referring to  FIG. 9 , a method for manufacturing the panel  12  by using a RIM process is described. At step S 9 . 1 , the mold tool (not shown) is opened. Optionally, at step S 9 . 2 , a release agent is applied by adding the in-mold release (IMR) agent to the mixture and/or by applying the external mold release (EMR) agent to one or both mold surfaces of the mold tool to assist in releasing the panel  12  from the mold tool upon completion of the mold cycle. Then, if desired, at step S 9 . 3 , an optional in-mold coating (IMC) is applied to a surface of the mold tool to provide a decorative surface finish to the panel  12 . The decorative surface finish may include any desirable aesthetic appearance with multiple colors or designs, such as streaking, splattering, pad printing, clouding, stone, marble, or the like. If it is determined that the IMC application at step S 9 . 3  is not desired, the desirable aesthetic appearance may be post-applied to the panel  12  upon completion of the mold cycle, if desired.  
      At step S 9 . 4 , the synthetic material is prepared prior to injection into the mold tool at step S 9 . 6 . For example, the isocynate and polyol may be separately maintained in a holding tank at a temperature approximately equal to 80° F., and then mixed together at the mixing head or injection nozzle. At step S 9 . 5 , the attachment member  24  can be placed onto the opposite surface of the mold tool as the IMC or cover material  20 . At step S 9 . 6 , the synthetic material is injected in the mold tool. A metered amount of synthetic material may be injected to yield a specific material density of the panel  12 . For example, if a higher density of the panel  12  is desired, a relatively larger amount of synthetic material is metered to substantially fill 100% of the volume of the mold tool. According to an embodiment, the synthetic material is injected for 1.9 seconds at a metering rate approximately equal to 300 gram per second (a total of 570 grams of synthetic material) to yield a high density panel  12 . As such, when foaming and expansion of the synthetic material occurs, a high density panel  12  may be yielded due to the compression of the synthetic material under tonnage of the closed mold tool. Preferably, a specific gravity of a high-density synthetic material is approximately equal to the range of about 0.60 to about 1.40. It will be appreciated that the invention is not limited by the metered amounts of synthetic material that is injected into the mold tool. For example, the synthetic material can be injected for 1.1 seconds at a metering rate approximately equal to 400 gram per second (a total of 440 grams of synthetic material) to fill a mold tool having dimensions of approximately 25″×25″× 3/16″.  
      Conversely, the synthetic material may be metered to yield a lower density panel  12  by injecting a relatively smaller amount of synthetic material that is less than 100% of the volume of the mold tool such that the synthetic material, upon injection, is permitted to expand into free space when the mold tool is closed. According to one embodiment of the invention, the synthetic material is injected for approximately 1.0 seconds at a metering rate approximately equal to 300 grams per second to yield a low density panel  12 . In an alternative embodiment, a lesser amount of synthetic material may be metered at step S 9 . 6  if a liquid, such as water, and the like, is introduced to the polyol component of the mixture. Upon introducing water to the polyol component, the cellular structure foams at a greater rate, which causes an even lower density of the panel  12 . According to one aspect of the invention, a specific gravity of a low-density synthetic material is approximately equal to the range of 0.10 to 0.60.  
      Upon metering and injecting the synthetic material, the mold tool surface is preferably heated to a temperature in the range approximately equal to 130-190° F. It will be appreciated that the mold tool surface temperature range may include different temperatures depending on the material of the mold tool surface. For example, if the mold tool surface is made of aluminum and is heated to approximately 140° F., the cure time may be approximately 60 sec. to approximately 3 min. At steps S 9 . 7  and S 9 . 8 , the mold tool is closed, and the synthetic material is cured to form the core  13  of the panel  12  made of synthetic material of unitary construction. Then, at step S 9 . 9 , the mold tool is opened and the panel  12  is removed from the mold tool.  
      A method for manufacturing the panel  12  by using a RRIM process is similar to the method for manufacturing the panel  12  using the RIM process, except that the reinforcing fibers  18  are introduced into the synthetic material prior to injecting the synthetic material into the mold tool at step S 9 . 6 .  
      Instead of forming the panel  12  using the RRIM process, a method for manufacturing the panel  12  by using a SRIM process is similar to the method for manufacturing the panel  12 , except that the scrim material  21  is placed on one or both mold halves of the mold tool prior to injecting the synthetic material into the mold tool at step S 9 . 6 .  
      A method for manufacturing the panel  12  having the cover material  20  can be formed by using the RIM, RRIM or SRIM process described above, except that the decorative cover  20  is introduced onto the surface of the mold tool instead of the IMC at step S 9 . 3 , thereby providing a decorative surface finish to the panel  12 .  
      The panel  12  may undergo additional, optional treatment operations once removed from the mold tool. For example, the panel may undergo a power washing step, a drying step, a clear coat application step, a clear coat baking step, and a package and shipping step. The clear coat may be applied in a single or multiple roll coating process steps. The clear coat improves weathering and UV resistance of the panel, especially when used as a floor or wall tile in residential or commercial applications.  
      It will be appreciated that these additional finishing steps may be omitted when making the final product. For example, if a low density synthetic material is prepared at step S 9 . 4 , the finishing procedure may only include an edge trimming operation after being removed from the mold tool. Then, the trimmed panel  12  may be packaged and shipped. In application, the panel  12  may be a ceiling tile applied to a drop ceiling grid (not shown) that is somewhat less rigidified and lighter in weight due to the low density composition of the synthetic material.  
      Several tests were conducted with the acoustical panel assembly  10  of the invention, as shown in  FIGS. 10 and 11 .  FIG. 10  shows the frequency response for a covered RIM panel  12  without reinforcement material and with a cover material  20  made of expanded PVC material with a layer of foam  21  between the RIM material and the cover material  20 , similar to the panel  12  shown in  FIG. 5 , and having a thickness of approximately 10 mm. The acoustic device  26  is mounted at the center of the panel  12 .  FIG. 11  shows the frequency response for a conventional ROHACELL® panel having a thickness of approximately 10 mm when the acoustic device is mounted at a location directly at the center of the panel.  
      The test results indicated that the best performance of the two tests conducted above was provided by the acoustical panel assembly  10  comprising a covered RIM panel  12  of the invention having no reinforcement material and a cover material made of expanded PVC material with a layer of foam between the RRIM material and the cover material, but when the acoustic device  26  was mounted at a location offset from the center of the panel  12 . This result was unexpected because it was believed that the conventional ROHACELL® panel should have provided the best performance based on the wide acceptance of the ROHACELL® panel material for it&#39;s acoustical properties when coupled with the acoustic device. However, the inventors have discovered, rather unexpectedly, that the material for the panel  12  produced by the SRIM process produced acceptable acoustical properties, and that the material for the panel  12  produced by the RIM process, and especially the panel  12  that was covered with expanded PVC and a layer of foam therebetween, produced exceptional acoustical performance. By discovering such an expected result, the inventors have discovered that the panel  12  produces superior acoustical properties, while providing the structural properties required for most automotive applications, such as for interior trim panels, and the like.  
      Another unexpected result discovered by the inventors is that better sound performance is achieved by mounting the acoustic device  26  not directly at the center of the panel  12 , but slightly offset from the center location. Specifically, the location for the acoustic device  26  for a rectangular or square-shaped panel can be obtained according to the following equation: 
 
Location=( 4/9) X , ( 3/7) Y  
          where,     X is the dimension of the panel along the x-axis, and     Y is the dimension of the panel along the y-axis.        

      For example, the location for the acoustic device  26  for a panel  12  having an x-dimension of 18 cm and a y-dimension of 14 cm would be 8 cm along the x-dimension and 6 cm along the y-dimension. In other words, the optimum location would be 1 cm offset from the center location (9 cm along the x-direction and 7 cm along the y-direction) in both the x- and y-dimensions.  
      The inventors have also discovered that superior performance is also unexpectedly achieved when the panel  12  of the invention has a core  13  made of low density material that is disposed between two layers of relatively thin, high density material, for example, a thin sheet of aluminum, or the like. In fact, the lower the density of the core  13  and the higher the relative density of the outer surface layers, the better the acoustical performance of the panel  12 . For example, it may be desirable that the core  13  be made of the synthetic material that includes voids, but still has the necessary structural properties for use in residential, commercial or automotive applications. For example, the panel  12  may comprise a core  13  having a honeycomb-shaped structure, an I-beam structure, and the like, disposed between layers of a metal, such as aluminum, and the like. The high density layers may be made of a variety of suitable materials, such as paper with or without resin material for bonding to the core, plastic material, glass veil composite skin material, and the like. The thickness of the high density layer may range between about 3 mm to about 5 mm. Other geometrically-shaped structures having the necessary structural properties and made of the synthetic material are within the scope of the invention.  
      While the invention has been specifically described in connection with certain specific embodiments thereof, it is to be understood that this is by way of illustration and not of limitation, and the scope of the appended claims should be construed as broadly as the prior art will permit.