Patent Publication Number: US-2023133780-A1

Title: Compact Air Plenum Silencer

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application 63/263,380, filed on Nov. 1, 2021, the entire contents of which is incorporated herein in its entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to heating, ventilation, and air-conditioning (HVAC) systems. In particular, a compact air plenum silencer for an HVAC system is disclosed. 
     BACKGROUND 
     HVAC systems are used to acclimatize the interior environment in closed spaces occupied by persons, such as in buildings and rooms. HVAC systems typically include an air handler to provide circulating air that is used to condition the interior climate of the buildings or rooms. The air handler may include various elements such as heat transfer elements, air filters, humidifiers, air blowers, dampers, and other devices. HVAC systems are typically designed for a specified performance rating, such as for providing a specified volumetric flow of air within the closed spaces. 
     In particular, the air handler may include a fan inlet cone, a fan unit and a discharge plenum. The fan unit in the air handler may include an inlet cone, a fan, a motor, a fan frame, and other control elements associated with the fan. One important design aspect of an HVAC system design is the management of noise and vibrations that components in the air handler may generate, including noise from the fan units, blower motors, ducts, air control dampers, and air outlets, among other noise sources. For example, a particular design of components in an HVAC system may be laid out to minimize noise, such as by placing noise generating equipment in locations where the impact of noise and vibrations is minimized for the occupants of the closed space. 
     In particular, it is known that the return air inlet is a source of noise transmission into the occupied closed spaces conditioned by an air handler. This noise coupling occurs because of physical proximity of noise sources, as noted above, in the fan unit to the inlet register at the return duct, and because of direct open air coupling within the return duct, which can be exacerbated by a straight line-of-sight return duct conduit to the blower motor, even though the return air flow occurs in a reverse direction to the noise transmission. 
     Accordingly, one known means to accomplish noise reduction in an air handler is to use one or more silencer elements within the return air duct conduit. Such silencers typically extend along the available line-of-sight in order to effectively attenuate resonant wavelengths related to the straight length of the conduit. Another known means to accomplish noise reduction in an air handler is to introduce an elbow joint in the return air duct conduit that eliminates the line-of-sight arrangement and reduces noise coupling as a result. 
     BRIEF SUMMARY 
     The terms “invention,” “the invention,” “this invention” and “the present invention” used in this patent are intended to refer broadly to all of the subject matter of this patent and the patent claims below. Statements containing these terms should be understood not to limit the subject matter described therein or to limit the meaning or scope of the patent claims below. Embodiments of the invention covered by this patent are defined by the below, not this summary. This summary is a high-level overview of various aspects of the invention and introduces some of the concepts that are further described in the Detailed Description section below. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used in isolation to determine the scope of the claimed subject matter. The subject matter should be understood by reference to appropriate portions of the entire specification of this patent, any or all drawings and each claim. 
     An embodiment of the present invention relates to an apparatus for reducing sound levels in an HVAC system, the apparatus including a housing configured to be positioned within an air inlet vent for an HVAC system. The housing includes a first opening configured to intake air and a second opening configured to output air and a plurality of baffles positioned within said housing, each baffle including a body defining a volume and has a plurality of perforations, wherein each baffle is affixed to the housing and wherein the plurality of perforations are configured to allow airflow through the volume of the body and redirecting sound waves. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The patent or application file contains at least one photograph or drawing executed in color. Copies of this patent or patent application publication with photographs or color drawing(s) will be provided by the Office upon request and payment of the necessary fee. 
       For a more complete understanding of the present invention and its features and advantages, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which: 
         FIG.  1    is a prior art depiction of a ceiling plenum with an air handler; 
         FIG.  2    is a depiction of a ceiling plenum with a compact air plenum silencer; 
         FIG.  3    is a depiction of a compact air plenum silencer in a perspective view; 
         FIG.  4    is a depiction of a compact air plenum silencer in an exploded view; 
         FIG.  5    is an image of a compact air plenum silencer; 
         FIG.  6    is a depiction of a compact air plenum silencer in a bottom view; 
         FIG.  7    is an image of a compact air plenum silencer; 
         FIGS.  8 A and  8 B  are depictions of a compact air plenum silencer; and 
         FIGS.  9 A and  9 B  are depictions of a compact air plenum silencer. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, details are set forth by way of example to facilitate discussion of the disclosed subject matter. It should be apparent to a person of ordinary skill in the field, however, that the disclosed embodiments are exemplary and not exhaustive of all possible embodiments. 
     Throughout this disclosure, a hyphenated form of a reference numeral refers to a specific instance of an element and the un-hyphenated form of the reference numeral refers to the element generically or collectively. Thus, as an example (not shown in the drawings), device “12-1” refers to an instance of a device class, which may be referred to collectively as devices “12” and any one of which may be referred to generically as a device “12”. In the figures and the description, like numerals are intended to represent like elements. 
     As noted above, conventional means for noise attenuation within a return air duct conduit have included long line-of-sight silencers that require a relatively large space, which is undesirable. The use of elbow j oints is another means for noise attenuation within a return air duct conduit. However, a simple elbow joint may be limited in the noise attenuation attained and may perform more poorly at noise attenuation that a line-of-sight silencer that works over longer attenuation distances. 
     As disclosed herein, a compact air plenum silencer may be used in place of an elbow joint in a return air duct conduit for noise attenuation. The compact air plenum silencer disclosed herein may enable noise attenuation by providing a 90 degree pathway for air flow and noise coupling in the return air duct conduit. The compact air plenum silencer disclosed herein may incorporate a plurality of internal baffle elements that induce internal reflection of incident sound waves, resulting in longer acoustical pathways as the incident sound traverses through the silencer. The longer acoustical pathways increase an attenuation time, and thus, dampening of the sound waves traversing through the silencer. In this manner, the compact air plenum silencer disclosed herein may provide a high degree of sound attenuation within a compact volume, which is desirable. Accordingly, the compact air plenum silencer disclosed herein may be particularly well suited for applications in which available space for air handling equipment is constrained, such as by available volume or cost per unit of volume. 
     Some approaches to noise reduction in HVAC systems have been disclosed in U.S. Pat. Nos. 10,309,302 B2 and 8,087,492 B2, which are incorporated by reference herein. 
     Referring now to the drawings,  FIG.  1    is a prior art depiction of a ceiling plenum  100  that may be present in a typical building as free space above a ceiling  102  of a room. It is noted that  FIG.  1    is a schematic illustration and is not necessarily drawn to scale or perspective. In ceiling plenum  100 , a return air conduit  106  is in fluid communication with an air handler  108 . Return air conduit  106  terminates at an opposing end with a return air duct  106 - 2  that is shown covered with a grille  104  to draw in return air and to enable the return air to be provided to air handler  108  in a direction given by arrow  110 . As shown, return air conduit  106  also includes an elbow joint  106 - 1  in fluid communication with return air duct  106 - 2  that is open and serves to redirect the return air that may be drawn in upwards (vertically) from return air duct  106 - 2  and redirected towards air handler  108  in horizontal direction  110 . Furthermore, noise emanating from air handler  108 , may propagate from various components included in air handler  108 , which may be different in particular embodiments, along return air conduit  106  in a direction opposite to arrow  110 . The noise may be attenuated by elbow joint  106 - 1  to a degree and may emerge into the room at grille  104 , in a direction and relative magnitude given by arrow  112 , which is undesirable. For example, elbow joint  106 - 1  may attenuate the noise by reflecting some noise power back towards air handler  108  within return air conduit  106 . However, a magnitude of noise introduced into the room below ceiling  102 , as given by arrow  112 , may still be larger than desired. In some implementations, a volume available for line-of-sight silencing equipment in ceiling plenum  100  may be constrained, such as by a limited space available for return air conduit  106 , for example. 
     In  FIG.  2   , a ceiling plenum  200  with a compact air plenum silencer  220 , as disclosed herein, is depicted. It is noted that  FIG.  2    is a schematic illustration and is not necessarily drawn to scale or perspective. In ceiling plenum  200 , an air handler  208  includes, among other elements, a return air duct  206  that is in fluid communication with air handler  208  via compact air plenum silencer  220 , to enable return air to be provided to air handler  208  in a direction given by arrow  210 - 2 . Return air duct  206  is shown covered by a grille  204  at an interior surface of ceiling  102 . As shown, compact air plenum silencer  220  may include various internal baffle elements, as will be described in further detail herein. As shown, compact air plenum silencer  220  also provides the 90-degree redirection functionality for return air (not shown or visible), which may be drawn into compact air plenum silencer  220  vertically, as given by arrow  210 - 1  and may emerge horizontally, as given by arrow  210 - 2 . Furthermore, noise emanating from air handler  208 , as described previously, may be coupled to compact air plenum silencer  220  in a direction opposite to arrow  210 - 2  and may pass through compact air plenum silencer  220 , where the noise may be attenuated to a large degree. Accordingly, a direction and relative magnitude of the noise emitted from compact air plenum silencer  220  at grille  204  into the room below ceiling  102  is given by an arrow  212 , which is shown smaller in magnitude than arrow  112  in prior art  FIG.  1   . The difference in magnitude between prior art arrow  112  and arrow  212  of compact air plenum silencer  220  may indicate that greater noise attenuation occurs with compact air plenum silencer  220  than with the operation of elbow joint  106 - 1  and conduit  106 , for the same or comparable conditions. 
     It is noted that ceiling plenums  100  and  200 , respectively shown in  FIGS.  1  and  2   , are exemplary embodiments for descriptive purposes and do not limit any application of compact air plenum silencer  220  to a particular arrangement or HVAC system design. For example, in various embodiments, compact air plenum silencer  220  may be used in different portions of a building or HVAC system, such as within a floor plenum below a floor, instead of within ceiling plenum  200  as depicted. 
     It is further noted that in some implementations, ceiling  102  may not be present and noise from air handler  108  may be directly coupled into an occupied space below air handler  108 . In various environments, a direction of return air flow given by a spatial orientation of grille  204  and return air duct  206  may vary from the vertical orientation of arrow  210 - 1  shown in  FIG.  2   . For example, when ceiling  102  is not present, return may be drawn in vertically downwards or horizontally or at an angle to vertical/horizontal. In some instances, return air duct  206  and grille  204  may be oriented or arranged or routed to avoid a physical barrier to the return air flow that may otherwise obstruct the return air. Because of the compact arrangement enabled by compact air plenum silencer  220 , as shown in  FIG.  2   , various such orientations and arrangements can be enabled, as desired, in order to minimize or optimize the space occupied by air handler  208 . 
     Referring now to  FIG.  3   , a perspective and detail view of compact air plenum silencer  220  is depicted. It is noted that  FIG.  3    is a schematic illustration and is not necessarily drawn to scale or perspective. As shown in  FIG.  3   , compact air plenum silencer  220  is fabricated in the form of a rectangular prism that may be physically dimensioned to correspond to any cross-sectional air inlet area for fluid communication with air handler  208 , as shown in  FIG.  2   . In some embodiments, the air plenum silencer  220  further includes a housing configured to contain the components of the air plenum silencer  220 . Said housing is positioned within the air inlet and dimensioned to correspond with the cross-sectional area of the air inlet and includes a first opening configured to intake air and a second opening configured to output air. In  FIG.  3   , a cover  304  of compact air plenum silencer  220  is visible at a top surface and also encloses a rear surface that is obscured from view. Also visible is a first side cover  306 - 1  of compact air plenum silencer  220  that encloses a first side, while a second side cover  306 - 2  that encloses a second side of compact air plenum silencer  220  is obscured from the perspective view. In  FIG.  3   , arrow  210 - 1  shows an air intake direction of compact air plenum silencer  220  that occurs via a bottom opening (not visible in  FIG.  3   , see  FIG.  5   ), while arrow  210 - 2  shows the air outlet direction, corresponding to  FIG.  2   , from a front opening. Also visible in  FIG.  3    and in enlarged portion A are baffle elements  302  that are placed in a particular orientation, dimension, and arrangement within compact air plenum silencer  220 . As shown in  FIGS.  3  -  6   , baffle elements  302  may be affixed to the housing and may further define a volume using an empty body, and, in some embodiments, said volume is filled with sound-attenuating media within compact air plenum silencer  220 . For example, the sound-attenuating media may be a porous material, like fiberglass, or a non-porous material, in particular applications with an elastic-type surface. In some cases, air spacer elements may be used to created internal compartments within baffle elements  302  that can dampen sound energy. The baffle elements  302  may additionally be perforated, for example at the bottom opening, as to allow airflow through the volume of the body of the baffle  302  attenuating sound waves. 
     The open area of the perforation may range from about 13% to about 51% in various embodiments. The particular orientation, dimension, and arrangement of baffle elements  302  within compact air plenum silencer  220 , as will be described in further detail herein, may enable compact air plenum silencer  220  to attenuate noise that is incident at the front opening. The range of 13% to about 51% is merely exemplary and additional ranges between 10% and 60% are envisioned within the scope of the present disclosure. 
     Referring now to  FIG.  4   , an exploded view of compact air plenum silencer  220  is depicted. It is noted that  FIG.  4    is a schematic illustration and is not necessarily drawn to scale or perspective. As shown in  FIG.  4   , various internal elements of compact air plenum silencer  220  are now visible. Under cover  304  and side covers  306 , an insulation layer  602  insulates the top and rear faces of compact air plenum silencer  220 . As shown in the example of  FIG.  4   , within compact air plenum silencer  220 , four (4) baffle elements  302  are visible. However, it is noted that different numbers of baffle elements may be used in different embodiments, for example, depending on a width of compact air plenum silencer  220 . Each baffle element  302  is shaped as a rectangular prism body and may be perforated at one or more of its sides to facilitate air flow, while also serving to reflect acoustical waves. As shown, each baffle element includes a nosepiece  302 - 1  that is closed and that faces the front opening where return air emerges from compact air plenum silencer  220 . Also shown in  FIG.  4    is a frame  608  that provides the inlet opening for compact air plenum silencer  220  and which supports baffle elements  302  internally within compact air plenum silencer  220 . Also visible in  FIG.  4    are side triangles  606  as well as center triangle  604 , which may further be additional perforated elements within compact air plenum silencer  220  such as within the housing. In some embodiments, the additional perforated elements may include a triangular element. As shown in  FIG.  6   , said triangular element may be positioned between two baffles and include a vertex formed by two sides forming a volume. Said volume may include sound-attenuating media as described above to further attenuate sound waves. In some embodiments, the triangular element may be positioned such that the vertex is proximal the transverse axis of the housing. 
     In  FIG.  5   , an image of compact air plenum silencer  220  formed from galvanized sheet metal is shown in an orientation standing with first side cover  306 - 1  down. In  FIG.  5   , the bottom opening and frame  608  of compact air plenum silencer  220  are visible, showing the bottom perforated faces of baffle elements  302 . Also visible in  FIG.  5    is the front opening of compact air plenum silencer  220  and respective nosepieces  302 - 1  of baffle elements  302 . 
     Referring now to  FIG.  6   , a bottom view of compact air plenum silencer  220  is depicted in which the placement and orientation of four (4) baffle elements  302  with respective nosepieces  302 - 1  are visible. In such embodiments, the housing may include a transverse axis with two of the baffles elements  302  located on a first side of the transverse axis and the remaining two baffle elements  302  located on a second side of the transverse axis. In some embodiments, it may be beneficial as to arrange the two baffles located on the first side of the transverse axis symmetrically in relation to the two baffles located on the second side of the transverse axis. It is noted that  FIG.  6    is a schematic illustration and is not necessarily drawn to scale or perspective. As shown in  FIG.  6   , compact air plenum silencer  220  may have an internal width W. Various other dimensions between the respective baffle elements  302  are shown in  FIG.  6    as dimensions X1, X2, X3, X4, X5, and X6, which may be selected for a particular performance or noise attenuation characteristics of compact air plenum silencer  220 . It is noted that while compact air plenum silencer  220  is shown herein in an exemplary embodiment having 4 baffle elements  302  for descriptive clarity, in other embodiments and implementations, compact air plenum silencer  220  may be fabricated to different dimensions with different numbers of baffle elements  302 . For example, the external and internal dimensions of compact air plenum silencer  220  may be selected for a given level of sound attenuation performance, or for noise damping of a given spectral portion of the acoustic noise. It is noted that the arrangement shown in  FIG.  6    is merely exemplary and a variety of orientations, number of baffle elements  302 , and arrangements are envisioned within the scope of this disclosure. 
     Specifically, in operation, compact air plenum silencer  220  may result in a differential pressure that is slightly greater than elbow joint  106 - 1 , for example, which is internally open, but which still represents a relatively low static pressure, and may be less than about 1 inch of water gage (WG), or more particularly, less than about 0.6 inch WG. In various embodiments, an air flow rate that compact air plenum silencer  220  can support may be from about 200 cubic feet/min. (cfm) to about 2,000 cfm. In typical applications, compact air plenum silencer  220  may be used for ambient air handling in an occupied building or room, and may accordingly be typically operated at ambient temperatures of between about 60° F. and about 85° F., or more specifically between about 65° F. and about 80° F. The indoor typical operating environment of compact air plenum silencer  220  may have about 50% humidity, which may vary according to various factors within a normal range of humidity for indoor conditions, for example. Furthermore, a frequency range over which compact air plenum silencer  220  may attenuate noise may be from about 100 Hz to about 5,000 Hz, or more specifically between about 125 Hz to about 4,000 Hz and may depend upon dimensions and configuration of the silencer. In a typical ceiling plenum of a commercial building, for example, during operation with air handler  208 , compact air plenum silencer  220  may result in an ambient noise level that is significantly reduced (see also Table 1). 
     In  FIG.  7   , an image of compact air plenum silencer  220  formed from galvanized sheet metal is shown in an orientation standing with first side cover  306 - 1  down. In  FIG.  7   , the bottom opening and top surface of cover  304  are visible, along with the front opening and respective nosepieces  302 - 1  of baffle elements  302  of compact air plenum silencer  220 . 
     In  FIGS.  8 A and  8 B  a top view and a side view, respectively, of air handler  208  attached to compact air plenum silencer  220  in one embodiment is depicted. In  FIGS.  8 A and  8 B , air handler  208  is equipped with a heating/cooling heat exchange unit for conditioning the return air flow, shown by arrows  210 . 
     In  FIGS.  9 A and  9 B  a top view and a side view, respectively, of air handler  208  attached to compact air plenum silencer  220  in one embodiment is depicted. In  FIGS.  9 A and  9 B , air handler  208  is equipped with a cooling coil for conditioning the return air flow (heat exchange unit), as shown by arrows  210 , and also includes a heating element that is mounted at one side, which may be used to heat supply air flow (not shown). 
     In Table 1 below, an amount of noise reduction in dB that compact air plenum silencer  220  may provide is given for 6 different octave bands versus fan airflow rates, in one exemplary embodiment. The measurements in Table 1 were obtained by measurement of sound levels in 6 octave bands radiated from the unit with and without the silencer attached. The measurements were taken in a reverberation chamber designed for such measurements and recorded in 1/3 octave bands and mathematically combined into full octave bands as required by the applicable standards for measuring air terminal units, such as ANSI/ASHRAE Standard 130-2016 for example. In particular, the values in Table 1 may indicate that attenuation performance of compact air plenum silencer  220  may improve with increasing sound levels. 
     
       
         
          TABLE 1
           
               
               
               
               
               
               
               
             
               
                 Noise reduction in decibels for different fan airflow rates and octave bands 
               
               
                 Fan Airflow [cfm] 
                 Octave 2 (125 Hz) 
                 Octave 3 (250 Hz) 
                 Octave 4 (500 Hz) 
                 Octave 5 (1,000 Hz) 
                 Octave 6 (2,000 Hz) 
                 Octave 7 (4,000 Hz) 
               
             
            
               
                 550 
                 3 
                 5 
                 6 
                 3 
                 5 
                 3 
               
               
                 800 
                 3 
                 5 
                 6 
                 5 
                 7 
                 6 
               
               
                 1,200 
                 2 
                 6 
                 7 
                 5 
                 8 
                 8 
               
               
                 1,600 
                 2 
                 6 
                 7 
                 6 
                 9 
                 11 
               
               
                 2,000 
                 2 
                 6 
                 7 
                 6 
                 9 
                 11 
               
            
           
         
       
     
     The above disclosed subject matter is to be considered illustrative, and not restrictive, and the appended claims are intended to cover all such modifications, enhancements, and other embodiments which fall within the true spirit and scope of the present disclosure. Thus, to the maximum extent allowed by law, the scope of the present disclosure is to be determined by the broadest permissible interpretation of the following claims and their equivalents, and shall not be restricted or limited by the foregoing detailed description. 
     Examples 
     A collection of exemplary embodiments, including at least some explicitly enumerates as “Examples” providing additional description of a variety of example types in accordance with the concepts described herein are provided below. These examples are not meant to be mutually exclusive exhaustive, or restrictive; and the invention is not limited to these examples but rather encompasses all possible modifications and variations within the scope of the issued claims and their equivalents. 
     Example 1. A sound reducing system for returning air to an air handler in an HVAC system, the sound reducing system including an air inlet having a cross-sectional area and in fluid communication with an air handler; a housing configured to be positioned within the air inlet and dimensioned to correspond with the cross-sectional area of the air inlet, wherein the housing includes a first opening configured to intake air and a second opening configured to output air; and a plurality of baffles positioned within the housing, each baffle including: a body defining a volume and having a plurality of perforations positioned thereon and facing the first opening, wherein each baffle is affixed to the housing, and wherein a sound-attenuating media is positioned within the volume; and wherein the plurality of perforations are configured to allow airflow through the volume of the body of the baffle while attenuating sound waves, and wherein the housing has a transverse axis and at least two baffles of the plurality of baffles are located on a first side of the transverse axis and at least two baffles of the plurality of baffles are located on a second side of the transverse axis. 
     Example 2. The sound reducing system of any of the preceding or subsequent examples or combination of examples, wherein the housing further includes a cover which covers a top face, a rear face, a first side, and a second side of the housing. 
     Example 3. The sound reducing system of any of the preceding or subsequent examples or combination of examples, further including an insulation layer positioned at the top face and the rear face. 
     Example 4. The sound reducing system of any of the preceding or subsequent examples or combination of examples, wherein the at least two baffles located on the first side of the transverse axis are arranged symmetrically to the at least two baffles located on the second side of the transverse axis with respect to the transverse axis of the housing. 
     Example 5. The sound reducing system of any of the preceding or subsequent examples or combination of examples, wherein the plurality of perforations of each baffle comprises an open area between 10% and 60% of a surface area of a side of the baffle having the plurality of perforations. 
     Example 6. An apparatus for reducing sound levels in an HVAC system, the apparatus including: a housing configured to be positioned within an air inlet vent for an HVAC system, wherein the housing includes a first opening configured to intake air and a second opening configured to output air; and a plurality of baffles positioned within said housing, wherein each baffle includes a body defining a volume and has a plurality of perforations; wherein each baffle is affixed to the housing; wherein the plurality of perforations are configured to allow airflow through the volume of the body and redirecting sound waves. 
     Example 7. The apparatus of any of the preceding or subsequent examples or combination of examples, wherein the volume of the body of each baffle comprises a sound-attenuating media. 
     Example 8. The apparatus of any of the preceding or subsequent examples or combination of examples, wherein the housing is dimensioned so as to correspond with a cross-sectional area of the air inlet. 
     Example 9. The apparatus of any of the preceding or subsequent examples or combination of examples, wherein the apparatus comprises at least four baffles. 
     Example 10. The apparatus of any of the preceding or subsequent examples or combination of examples, wherein the housing has a transverse axis and at least two baffles are located on a first side of the transverse axis and at least two baffles are located on a second side of the transverse axis. 
     Example 11. The apparatus of any of the preceding or subsequent examples or combination of examples, wherein the four baffles are arranged symmetrically with respect to the transverse axis of the housing. 
     Example 12. The apparatus of any of the preceding or subsequent examples or combination of examples, further including a plurality of additional perforated elements positioned within the housing. 
     Example 13. The apparatus of any of the preceding or subsequent examples or combination of examples, wherein at least one of the plurality of additional perforated elements comprises at least one triangular element. 
     Example 14. The apparatus of any of the preceding or subsequent examples or combination of examples, wherein the triangular element comprises a vertex formed by two sides and the vertex is proximal the transverse axis of the housing and is located between two of the baffles. 
     Example 15. The apparatus of any of the preceding or subsequent examples or combination of examples, wherein the triangular element further defines a volume, wherein the volume comprises a sound-attenuating media. 
     Example 16. The apparatus of any of the preceding or subsequent examples or combination of examples, wherein the body of each baffle comprises a rectangular prism shape. 
     Example 17. The apparatus of any of the preceding or subsequent examples or combination of examples, wherein each baffle additionally includes a nosepiece positioned proximal the second opening of the housing. 
     Example 18. The apparatus of any of the preceding or subsequent examples or combination of examples, wherein the plurality of perforations of each baffle comprises an open area between 10% and 60% of a surface area of a side of the baffle having the plurality of perforations. 
     Example 19. The apparatus of any of the preceding or subsequent examples or combination of examples, wherein the housing further includes a top face, a rear face, a first side, and a second side. 
     Example 20. The apparatus of any of the preceding or subsequent examples or combination of examples, wherein the housing further includes a cover which covers the top face, the rear face, the first side, and the second side. 
     Example 21. The apparatus of any of the preceding or subsequent examples or combination of examples, further including an insulation layer positioned at the top face and the rear face. 
     Example 22. The apparatus of any of the preceding or subsequent examples or combination of examples, wherein the housing further includes a frame positioned proximal the first opening, the frame configured to support the plurality of baffles. 
     Embodiments of the invention have been described for illustrative and not restrictive purposes, and alternative embodiments will become apparent to readers of this patent. Accordingly, the present invention is not limited to the embodiments described above or depicted in the drawings, and various embodiments and modifications can be made without departing from the scope of the invention. 
     Although certain exemplary embodiments of the disclosure have been shown and described in detail, it should be understood that various changes and modifications may be made therein without departing from the scope of the appended claims. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. 
     It must be noted that as used herein and in the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Although the terms “first,” “second,” etc., may be used herein to describe various elements, components, regions, layers and/or sections, it should be understood that they should not be limited by these terms. These terms are used only to distinguish one element, component, region, layer, or section from another region, layer, or section. Thus, a first element, component, region, layer, or section discussed above could be termed a second element, component, region, layer, or section without departing from the teachings of the present invention.