Abstract:
An acoustic dampening panel comprising: (a) a first layer of expanded polypropylene; (b) a solid layer having a surface weight between 2.4 kilograms per meter squared and 25 kilograms per meter squared; and, (c) a second layer of expanded polypropylene, where the first and second layers of expanded polypropylene sandwich the solid layer therebetween. The acoustic dampening panel may further comprise a fourth layer comprising a metal skin, where the solid layer and the metal skin sandwich the second layer therebetween.

Description:
RELATED ART 
     1. Field of the Invention 
     The invention is directed to acoustic barriers and, more specifically, to acoustic barriers comprising a multi-layer construction. 
     2. Brief Discussion of Related Art 
     Heating or cooling equipment employing a compressor is plagued by loud noise levels in the low frequency region. Yet this same heating and cooling equipment are required to meet certain noise levels for residential and commercial applications. Prior acoustic insulation comprised a standard sheet metal layer with a fiberglass backer panel. But this acoustic insulation resonates due to an excitation frequency originating at the compressor. Thus, there is a need for an effective acoustic barrier or dampener to prevent or reduce airborne noise transmission into the space the equipment is intended to condition. 
     INTRODUCTION TO THE INVENTION 
     The invention is directed to acoustic barriers and dampeners. In exemplary form, the embodiments disclosed herein utilize a multi-layer configuration of insulating layers. These insulating layers may be mounted to an outer skin in order to provide a single, integrated structure. By way of example, the multi-layer configuration may make use of multiple polymer layers comprising polypropylene and vinyl. More specifically, an exemplary multi-layer configuration may include a layer of high density expanded polypropylene, a layer of mass loaded vinyl, and a layer of low density expanded polypropylene. 
     The exemplary multi-layer configurations disclosed herein provide an effective acoustic barrier or dampener for use as panels in heating, ventilation, and air conditioning (HVAC) applications. The layout, densities, and thicknesses of the layers are operative to create a reduction in airborne noise between 60 and 10,000 Hz. The exemplary embodiments disclosed herein are also effective at low frequency attenuation through the reduction of resonances at the outer panel surface, when an outer panel is utilized (such as a metal panel). 
     It is a first aspect of the invention to provide an acoustic dampening panel comprising: (a) a first layer of expanded polypropylene; (b) a solid layer having a surface weight between 2.4 kilograms per meter squared and 25 kilograms per meter squared; and, (c) a second layer of expanded polypropylene, where the first and second layers of expanded polypropylene sandwich the solid layer therebetween. 
     In a more detailed embodiment of the first aspect, the first layer comprises high density expanded polypropylene. In yet another more detailed embodiment, the high density expanded polypropylene has a thickness between five to twenty millimeters. In a further detailed embodiment, the solid layer comprises mass loaded vinyl. In still a further detailed embodiment, the mass loaded vinyl has a thickness between two to six millimeters. In a more detailed embodiment, the second layer comprises low density, porous expanded polypropylene. In a more detailed embodiment, the low density, porous expanded polypropylene has a thickness between five to thirty millimeters. In another more detailed embodiment, the panel further includes a fourth layer comprising a metal skin, wherein the solid layer and the metal skin sandwich the second layer therebetween. In yet another more detailed embodiment, the metal skin comprises at least one of an aluminum layer, an aluminum alloy layer, and a substrate coated with aluminum. In still another more detailed embodiment, the metal layer has a thickness between 0.5 to 1.25 millimeters. 
     In yet another more detailed embodiment of the first aspect, the panel further includes an adhesive interposing at least two of the layers. In still another more detailed embodiment, the metal skin includes a sheet portion parallel and spaced apart from a flange and, the flange and the sheet portion sandwich the first layer of expanded polypropylene, the solid layer, and the second layer of expanded polypropylene therebetween. 
     It is a second aspect of the invention to provide a method of acoustically insulating a device, the method comprising: (a) enclosing a device using a plurality of acoustic dampening panels, wherein at least one of the plurality of acoustic dampening panels comprises: (i) a first layer of expanded polypropylene; (ii) a solid layer having a surface weight between 2.4 kilograms per meter squared and 25 kilograms per meter squared; and, (iii) a second layer of expanded polypropylene, where the first and second layers of expanded polypropylene sandwich the solid layer therebetween. 
     In a more detailed embodiment of the second aspect, the device comprises at least one of a heating device, a ventilation device, and an air conditioning device. In yet another more detailed embodiment, the device comprises a compressor. In a further detailed embodiment, the step of enclosing the device includes mounting the plurality of acoustic dampening panels together using at least one of fixation tabs, fixation detents, and an adhesive. 
     It is a third aspect of the invention to provide an acoustic dampening panel comprising: (a) a first layer of expanded polypropylene; (b) a second layer of mass loaded vinyl; and, (c) a third layer of expanded polypropylene, where the first and third layers of expanded polypropylene sandwich the solid layer therebetween. 
     In a more detailed embodiment of the third aspect, the panel further includes a fourth layer comprising a metal skin, wherein the second layer and the metal skin sandwich the third layer therebetween. In yet another more detailed embodiment, the metal skin includes a sheet portion parallel and spaced apart from a flange and, the flange and the sheet portion sandwich the first layer of expanded polypropylene, the second layer of mass loaded vinyl, and the third layer of expanded polypropylene therebetween. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view showing the layers of the first exemplary acoustic barrier. 
         FIG. 2  is an elevated perspective view of an exemplary acoustic enclosure shown without a top, a bottom, one side wall, and an outer skin. 
         FIG. 3  is a magnified, elevated perspective cut-away view showing the position of a deflectable tab when the respective layers have been removed. 
         FIG. 4  is an elevated, cross-sectional view of the first exemplary acoustic barrier of  FIG. 1  showing the orientation of the deflectable tab and the respective layers. 
         FIG. 5  is an elevated perspective view of a joint between the outer skin and the respective layers. 
     
    
    
     DETAILED DESCRIPTION 
     The exemplary embodiments of the invention are described and illustrated below to encompass acoustic barriers or dampeners. Of course, it will be apparent to those of ordinary skill in the art that the embodiments discussed below are exemplary in nature and may be reconfigured without departing from the scope and spirit of the invention. However, for clarity and precision, the exemplary embodiments as discussed below may include optional steps, methods, and features that one of ordinary skill should recognize as not being a requisite to fall within the scope of the invention. 
     Referencing  FIG. 1 , an exemplary configuration  100  that may be used as an acoustic barrier or dampener comprises multiple layers of acoustic insulation. This configuration allows for the reduction of any excitation frequencies before reaching the outermost panel or layer, thereby significantly reducing sound radiated from the configuration surfaces into the surrounding environment. 
     In exemplary form, the configuration  100  comprises a first innermost layer  102  of high density expanded polystyrene or expanded polypropylene (EPP) mounted to a layer of mass loaded vinyl  104 , which is itself mounted to a low density, porous EPP layer  106 . The respective layers  102 ,  104 ,  106  have a generally uniform thickness across a respective length and width, characterized by thicknesses of the high density EPP layer  102  being between 5-20 millimeters, thicknesses of the mass loaded vinyl layer  104  being between 2-6 millimeters, and thicknesses of the low density, porous EPP layer  106  being between 5-30 millimeters. The layers  102 ,  104 ,  106  are positioned adjacent one another so that the EPP layers  102 ,  106  sandwich the vinyl layer  104  therebetween. In order to retain the layers  102 ,  104 ,  106  in an adjacent relationship, an adhesive may be applied to the exposed surfaces of the layers coming in contact with one another for form a mechanical bond between the layers. 
     Alternatively, or in addition, the exemplary configuration  100  may include an outer skin  110  to maintain the layers in an adjacent relationship. By way of example, the skin  110  may be fabricated from a sheet metal of any gauge such as, without limitation, steel, alloyed steel, coated steel, aluminum, alloyed aluminum, and coated aluminum. By way of example, and not limitation, the skin may have a thickness between 0.5-1.25 mm. The outer skin  110  is operative to reduce the sound transmission via mass dampening and provides a sealed surface. This sealed surface prevents or retards air leakage and subsequent airborne noise radiation. 
     The innermost EPP layer  102  is operative to absorb initial acoustic energy emanating from the surroundings. By way of example, the exemplary configuration  100  may be used to form an enclosure around an HVAC device. The innermost EPP layer  102  absorbs acoustic energy emanating from the HVAC device. 
     The mass loaded vinyl layer  104  serves as a mass-dampening sound transmission reduction layer. 
     The low density, porous EPP layer  106  is operative to absorb remaining low frequency acoustic energy. 
     The thicknesses, masses, and densities of the layers  102 ,  104 ,  106  can be adjusted for optimal noise reduction in the air-handling (broadband) and condensing (low frequency) sections. As set forth below in Equation #1, an empirical diffuse field equation sets forth the relationship between sound reduction (i.e., sound transmission loss) and thickness and density of the sound barrier. 
                   TL   =       10   *       Log   10     ⁡     (       (     1   +         ρ   b     ⁢   h   ⁢           ⁢   ω       2   ⁢   ρ   ⁢           ⁢   c         )     2     )         -   5             Equation   ⁢           ⁢   #1               
where:
 
TL=Transmission Loss (dB)
 
ρb=Barrier Density
 
h=Barrier Thickness
 
ω=2*pi*Frequency
 
ρc=acoustic impedance of air
 
     Referring to  FIG. 2 , the exemplary configuration  100  may be used as an acoustic enclosure  120  that surrounds or partially surrounds a motor or other potential sound emitting device. In such a circumstance, the enclosure  120  may include an internal skeleton or frame  122  that is mounted to the exemplary configuration  100  to impart greater rigidity and support to the enclosure. In particular, the innermost EPP layer  102  is molded to include channels  126  that receive portions of the frame  122  in order to mount the frame to the innermost EPP layer. 
     Referencing  FIGS. 3 and 4 , the exemplary acoustic enclosure  120  includes a sheet metal outer skin  110 . In order to attach the outer skin  110  to the respective layers  102 ,  104 ,  106 , the outer skin includes a series of cutouts  128  that define deflectable tabs  130 . In exemplary form, the tabs are deflected inward toward the location where the respective layers  102 ,  104 ,  106  will be located prior to the layers being received within a cavity formed by the outer skin  110 . However, it should also be noted that the tabs may be deflected after the outer skin  110  receives the respective layers  102 ,  104 ,  106 . 
     Referring to  FIG. 5 , it is preferable that gaps in the joints between the respective layers  102 ,  104 ,  106  and the outer skin  110  be minimized. Accordingly, it is also within the scope of the disclosure to provide the outer skin  110  with one or more detent receivers  132  that are adapted to engage one or more detents  134  mounted to the respective layers  102 ,  104 ,  106 . In this manner, the layers may be compressed against the outer skin  110  and held in this position. It should also be noted that the deflectable tabs  130  may be used in lieu of or in addition to the detents  134  and detent receivers  132 . 
     Following from the above description and invention summaries, it should be apparent to those of ordinary skill in the art that, while the methods and apparatuses herein described constitute exemplary embodiments of the invention, the invention is not limited to the foregoing and changes may be made to such embodiments without departing from the scope of the invention as defined by the claims. Additionally, it is to be understood that the invention is defined by the claims and it is not intended that any limitations or elements describing the exemplary embodiments set forth herein are to be incorporated into the interpretation of any claim element unless such limitation or element is explicitly stated. Likewise, it is to be understood that it is not necessary to meet any or all of the identified advantages or objects of the invention disclosed herein in order to fall within the scope of any claims, since the invention is defined by the claims and since inherent and/or unforeseen advantages of the invention may exist even though they may not have been explicitly discussed herein.