Abstract:
A ventilation duct and methods of ventilation are disclosed. The ventilation duct provides a plurality of inner and outer sound absorbing members. The inner and outer sound absorbing members lying in separate planes with portions of the inner and outer sound absorbing members overlapping one another to inhibit the transmission of sound through the duct. The inner and outer sound absorbing members each including a longitudinal cavity filled with a sound absorbing material and having a plurality of sound transmission passages extending through the members to expose the sound absorbing material to incoming sound waves. In addition, the members may be shaped to have a reverse megaphone effect to further reduce the sound transmitted across the duct.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    The present application is a continuation-in-part of co-pending Provisional Application Ser. No. 60/258,862, filed Dec. 29, 2000 and entitled “Duct Silencer.” 
     
    
     
       BACKGROUND  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to ventilation ducts and, more particularly, to ducts providing both ventilation and noise abatement.  
           [0004]    2. Description of the Related Art  
           [0005]    Ventilation ducts are frequently incorporated into various structures to allow the ventilation of gases and vapors from the structures or to allow air into the structures. In buildings or structures including machinery or equipment that produce toxic or noxious exhaust, the free flow of air through the ducts can be critical. Further, the ventilation of these structures can be important for cooling the machinery or equipment housed in the structures. Many current ventilation ducts and related ventilation systems have a significant pressure drop as the gases or vapors pass from one side of the duct to the other. This pressure drop is a function of the resistance to the flow of the gases or vapors through the duct and, hence, through the housing which is being ventilated. The resistance to air flow decreases the efficiency that the gases or vapors are ventilated from the structures and, when machinery or equipment producing toxic or noxious exhaust is housed within the structure, the resistance to air flow increases the concentration of toxic or noxious exhaust within the structures. Further, the increased resistance decreases the inflow and outflow air. When the equipment or machinery utilizes a combustion engine, the decreased supply of oxygen resulting from inefficient ventilation can reduce the efficiency of the engines. The inflow of oxygen is particularly important when the combustion engine substantially fills the interior volume of the housing, such as when the housing is integral with heavy machinery, such as, for example, loaders and bulldozers, or when the housing is a substructure on the rooftop of a larger building to house unsightly or noisy equipment, such as, for example, generators. Similarly, the flow of air generally through housings is important for cooling equipment and machinery, such as, for example, air conditioning units and combustion engines. In addition, when a structure is actively rather than passively ventilated, the free flow of air through the ducts is critical for a low pressure drop. A lower pressure drop reduces the load on the fan removing air from the structure. Thus, the more freely the air flows through the ducts of an air inlet, the less powerful the fan has to be to meet its performance requirements. Typically, lower capacity fans are less costly than the higher performance fans and the reduced load on the fan typically results in less wear. Therefore, a need exists for a ventilation duct that provides a limited pressure drop as gases and/or vapors pass through the duct.  
           [0006]    Further, noise pollution is a growing problem. Frequently, equipment and machinery are noisy and, in some cases, extremely noisy and therefore, contribute to the problem of noise pollution. The noise from equipment and machinery can be distracting to those working in close proximity to the equipment or machinery. The distraction can reduce the productivity for these individuals and, when extremely noisy, can damage the hearing of individuals regularly exposed to the noise levels. Reduced productivity and injured workers can reduce profitability and may result in expensive lawsuits. In addition, noisy equipment can decrease the ability of workers to communicate with one another when in close proximity to the equipment or machinery. In certain work environments, such as, for example, construction zones or industrial facilities, the inability to effectively communicate potential dangers can result in injury to workers or in some cases the death of a worker or workers. City and/or county codes can also require that noise levels be kept below a certain level for at least a part of the day. To minimize the noise, machinery is frequently isolated within a housing or segregated behind a wall to absorb the sound. However, these housings and walls frequently require ventilation ducts to allow for proper ventilation of the equipment or machinery. Therefore, a need exists for a ventilation duct that inhibits the transmission of sound from one side of the duct to the other side of the duct.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention meets the above needs and provides additional improvements and advantages that will be recognized by those skilled in the art upon review of the present disclosure. In one aspect, a ventilation duct in accordance with the present invention includes a frame to which is mounted a plurality of inner sound absorbing members and a plural of outer sound absorbing members. The plurality of inner sound absorbing members are secured to the frame within a first plane. The plurality of outer sound absorbing members are secured to the frame within a second plane. The first plane being substantially parallel to the second plane. The outer members are secured in the frame such that at least a portion of each outer members overlaps with at least of portion of an inner member to inhibit the transmission of sound. To further inhibit the transmission of sound across the ventilation duct, each of the inner sound absorbing members and the outer sound absorbing members can define a longitudinal cavity that is filled with a sound absorbing material. The inner sound absorbing member including a plurality of sound transmission passages between the outer surface to the longitudinal cavity to direct sound into the longitudinal cavity for sound abatement by the sound absorbing material with the plurality of sound transmission passages on an inner region of the outer sound absorbing members.  
           [0008]    In another aspect of the present invention, a housing includes a ventilation duct. The ventilation duct having a plurality of inner sound absorbing members and a plural of outer sound absorbing members secured to a wall of the housing. The plurality of inner sound absorbing members are secured to the wall within a first plane. The plurality of outer sound absorbing members are secured to the wall within a second plane. The first plane being substantially parallel to the second plane. The outer members are secured in the frame such that at least a portion of each outer members overlaps with at least of portion of an inner member to inhibit the transmission of sound. To further inhibit the transmission of sound across the ventilation duct, each of the inner sound absorbing members and the outer sound absorbing members can define a longitudinal cavity that is filled with a sound absorbing material. The inner sound absorbing member including a plurality of sound transmission passages between the outer surface to the longitudinal cavity to direct sound into the longitudinal cavity for sound abatement by the sound absorbing material with the plurality of sound transmission passages on an inner region of the outer sound absorbing members.  
           [0009]    It is thus an object of the present invention to provide novel apparatus and methods for ventilating a structure.  
           [0010]    It is further an object of the present invention to provide such novel apparatus and methods that reduces the pressure drop as gases and vapors pass through a ventilation duct.  
           [0011]    It is further an object of the present invention to provide such novel apparatus and methods that inhibit the passage of sounds through a ventilation duct.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    The illustrative embodiments may best be described by reference to the accompanying drawings where:  
         [0013]    [0013]FIG. 1 illustrates a perspective view of an embodiment of a housing in accordance with the present invention;  
         [0014]    [0014]FIG. 2 illustrates a perspective view of an embodiment of an apparatus in accordance with the present invention;  
         [0015]    [0015]FIG. 3A illustrates a side view in cross-section of an of an embodiment in accordance with the present invention;  
         [0016]    [0016]FIG. 3B illustrates a side view in cross-section of another embodiment in accordance with the present invention;  
         [0017]    [0017]FIG. 3C illustrates a side view in cross-section of yet another embodiment in accordance with the present invention;  
         [0018]    [0018]FIG. 4A illustrates a detailed cross-section of an inner sound absorbing member in accordance with the present invention; and  
         [0019]    [0019]FIG. 4B illustrates a detailed cross-section of an outer sound absorbing member in accordance with the present invention. 
     
    
       [0020]    All Figures are drawn for ease of explanation of the basic teachings of the present invention only; the extensions of the Figures with respect to number, position, relationship and dimensions of the parts to form the preferred embodiment will be explained or will be within the skill of the art after the following description has been read and understood. Further, the exact dimensions and dimensional proportions to conform to specific force, weight, strength, and similar requirements will likewise be within the skill of the art after the following description has been read and understood.  
         [0021]    Where used in various Figures of the drawings, the same numerals designate the same or similar parts. Furthermore, when the terms “top,” “bottom,” “right,” “left,” “forward,” “rear,” “first,” “second,” “inside,” “outside,” and similar terms are used, the terms should be understood to reference only the structure shown in the drawings as it would appear to a person viewing the drawings and utilized only to facilitate describing the illustrated embodiment.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0022]    [0022]FIG. 1 illustrates an embodiment of a housing  10  in accordance with the present invention. Housing  10  may be configured to house one or more piece of machinery, may be sized to house a plurality of pieces of machinery and workers to operate the machinery, or may be otherwise configured as will be recognized by those skilled in the art. Further, housing  10  may be configured for permanent or temporary placement at a desired location or may be configured for placement on heavy equipment such as, for example, top loaders, bulldozers and cranes. Housing  10  generally includes one or more walls  12  with at least one of walls  12  including a ventilation duct  20 . Housing  10  can also include a roof  14 . Roof  14  is illustrated as sloped for exemplary purposes only. As illustrated for exemplary purposes, housing  10  includes four walls  12 . Typically, when housing  10  includes four walls to form an enclosure, housing  10  will also include a door  16  to provide access to the equipment, machinery or other items housed within housing  10 . Walls  12 , roof  14  and door  16  are generally constructed to enclose machinery or equipment and may be constructed from materials designed to promote ventilation and/or to retain sound emitted from the equipment or machinery. Ventilation ducts  20  can be sized and positioned within housing  10  to best facilitate ventilation and/or sound abatement. Ventilation ducts  20  are typically positioned within the walls but, may also be positioned in door  16  or roof  14 . The specific sizing and positioning of ventilation ducts  20  will depend on the particular application and will be recognized by those skilled in the art upon review of the present disclosure.  
         [0023]    [0023]FIG. 2 illustrates a perspective view of an embodiment of a ventilation duct  20  in accordance with the present invention. Ventilation duct  20  of FIG. 2 is shown with the ends of sound absorbing members  22   a  and  22   b  unsecured for illustrative purposes. Typically, sound absorbing members  22   a  and  22   b  are secured to a wall  12  of housing  10  or to a frame  18  to support the sound absorbing members  22   a  and  22   b . In use, a side plate may be provided to enclose and/or support sound absorbing members  22   a  and  22   b . Sound absorbing members  22   a  and  22   b  are generally spaced from one another to allow the passage of gases or vapors while minimizing the pressure drop between an inner surface  24  and an outer surface  26  of ventilation duct  20 . Generally, ventilation ducts  20  include a plurality of inner sound absorbing members  22   a  substantially positioned with a first plane and a plurality of outer sound absorbing members  22   b  substantially positioned with a second plane. The first plane and the second plane are substantially parallel to one another and spaced from one another along a perpendiculars to both planes. Inner sound absorbing members  22   a  and outer sound absorbing members  22   b  are shown as straight and elongated and with each member arranged in parallel within other members within their respective planes for exemplary purposes only. Inner sound absorbing members  22   a  and outer sound absorbing members  22   b  are generally positioned relative to one another within the inner and outer planes to permit ventilation while inhibiting the transmission of sound between an inner surface  24  and an outer surface  26  of ventilation duct  20 . To inhibit the transmission of sound, inner sound absorbing members  22   a  and outer sound absorbing members  22   b  positioned within their respective planes so that there is an continuous overlap  50 , best illustrated in FIGS. 3A, 3B and  3 C, between at least a portion of outer sound absorbing members  22   b  and inner sound absorbing members  22   a . Overlap  50  is an overlap of the members in opposing planes along an axis perpendicular to the planes in which the members substantially lie. Thus, overlap  50  inhibits the direct transmission of sound along the perpendicular between inner surface  24  and outer surface  26  of ventilation duct  20 .  
         [0024]    The cross-sectional profile of inner sound absorbing members  22   a  and outer sound absorbing members  22   b , cumulatively referred to as sound absorbing members  22   a  and  22   b , are generally configured to cooperatively reflect sound toward the inner surface of ventilation duct  20 . As illustrated in FIG. 3A, sound absorbing members  22   a  and  22   b  have a trapezoidal cross-section shape. As illustrated in FIG. 3B, sound absorbing members  22   a  and  22   b  have a triangular cross-section shape. As illustrated in FIG. 3C, sound absorbing members  22   a  and  22   b  have a semicircular cross-section shape. Regardless of cross-sectional shape, the sound absorbing members  22   a  and  22   b  are positioned relative to one another to reflect sound originating from the side of inner surface  24  of ventilation duct  20  back toward inner surface  24  side of ventilation duct  20 . As illustrated in FIGS. 3A, 3B and  3 C, sound absorbing members  22   a  and  22   b  are positioned so that the apexes or shorter sides of the cross-sectional profiles for inner sound absorbing members  22   a  and outer sound absorbing members  22   b  are opposing one another. The positioning of the apexes or shorter sides of the cross-sectional shapes opposing one another as illustrated creates a reverse megaphone effect to further inhibit the transmission of sound across the duct. Further, the sound absorbing members  22   a  and  22   b  are spaced to permit ventilation through ventilation passage  52 . Ventilation passage  52  generally being the space within ventilation duct  20  permitting the ventilation of gases or vapors between inner surface  24  and outer surface  26  of ventilation duct  20 .  
         [0025]    [0025]FIG. 4A illustrates detailed cross-section of an embodiment of an inner sound absorbing member  22   a  in accordance with the present invention. Inner sound absorbing member  22   a  defines an outer surface  42 , a longitudinal cavity  44  and a plurality of sound transmission passage  46 . Typically, inner sound absorbing members  22   a  may be constructed materials such as galvanized steel, fiberglass, plastics or other materials capable of withstanding the physical environment which ventilation duct  20  will be exposed. In one aspect, inner sound absorbing members  22   a  may be constructed of a sound absorbing material. Outer surface is illustrated with a trapezoidal cross-section for exemplary purposes. When trapezoidal, the angle  48  at the junction of inside wall  60  and a side wall  62  or  66  may be selected to provide a reverse megaphone effect when positioned in a ventilation duct  20  in accordance with the present invention. To provide the reverse megaphone effect, angle  48  could be, for example, 55 degrees or other angles that will be recognized by those skilled in the art. To further reduce sound transmission, inner sound absorbing members  22   a  may be provided with a plurality of sound transmission passages  46 . Sound transmission passages  46  may extend from outer surface  42  of inner sound absorbing members  22   a  to longitudinal cavity  44 . Sound transmission passages  46  may be round, square, triangular, irregular or otherwise shaped to permit the passage of sound to the longitudinal cavity  44 . Generally, sound transmission passages  46  are positioned and concentrated to absorb the direct and reflected sounds arising from inner surface  24  side of ventilation duct  20 . As illustrated, inner sound absorbing members  22   a  includes sound transmission passages  46  on an inside wall  60 , a left end wall  62 , an outside wall  64  and a right end wall  66 . In one aspect, sound transmission passages  46  may be of sufficient size and number to result in an outer surface  42  that is at least 40% open to longitudinal cavity  44 . Longitudinal cavity  44  extends for at least a portion of the length of inner sound absorbing members  22   a . In one aspect, longitudinal cavity  44  may be filled with a sound absorbing material  45 . Sound absorbing material  45  may be any number of natural or synthetic materials known to those skilled in the art to effectively absorb sound. For example, sound absorbing material  45  may be such as mineral wool or fiber glass. If mineral wool, the mineral wool could be packed within longitudinal cavity  44  at eight pounds per cubic foot or to otherwise packed to efficiently absorb sound as will be recognized by those skilled in the art upon review of the present disclosure.  
         [0026]    [0026]FIG. 4B illustrates an embodiment of an outer sound absorbing member  22   b  in accordance with the present invention. Outer sound absorbing member  22   b  defines an outer surface  42 , a longitudinal cavity  44  and a plurality of sound transmission passage  46 . Typically like inner sound absorbing members  22   a , outer sound absorbing members  22   b  may be constructed materials such as galvanized steel, fiberglass, plastics or other materials capable of withstanding the physical environment which ventilation duct  20  will be exposed. In one aspect, outer sound absorbing member  22   b  may be constructed of a sound absorbing material. Outer surface is illustrated with a trapezoidal cross-section for exemplary purposes. When trapezoidal, the angle  48  at the junction an outside wall  74  and a side wall  72  or  76  may be selected to provide a reverse megaphone effect when positioned in a ventilation duct  20  in accordance with the present invention. To provide the reverse megaphone effect, angle  48  could be, for example, 55 degrees or other angles that will be recognized by those skilled in the art. To further reduce sound transmission, outer sound absorbing member  22   b  may be provided with a plurality of sound transmission passages  46  as described with respect to inner sound absorbing member  22   a . Generally, sound transmission passages  46  for outer sound absorbing member  22   b  are also positioned and concentrated to absorb the direct and reflected sounds arising from inner surface  24  side of ventilation duct  20 . As illustrated, outer sound absorbing member  22   b  includes sound transmission passages  46  on an inside wall  70 , a left end wall  72 , and a right end wall  76 . Collectively, inside wall  70 , a left end wall  72 , and a right end wall  76  of outer sound absorbing member  22   b  are referred to as an inner region of outer sound absorbing member  22   b . In one aspect, sound transmission passages  46  may be of sufficient size and number to result in outer surface  42  of the inner region of outer sound absorbing member  22   b  having at least 40% open to longitudinal cavity  44 . As with inner sound absorbing member  22   a , longitudinal cavity  44  of outer sound absorbing member  22   b  extends for at least a portion of the length of outer sound absorbing member  22   b . Also like inner sound absorbing member  22   a , longitudinal cavity  44  of outer sound absorbing member  22   b  may be filled with a sound absorbing material  45  as described above.  
         [0027]    Since the invention disclosed above may be embodied in other specific forms without departing from the spirit or general characteristics of the invention, some of which forms have been indicated, the embodiments described in the present disclosure are to be considered in all respects illustrative and not restrictive. The scope of the invention is to be indicated by the appended claims, rather than by the above description, and all changes which come within the meaning and range of equivalency of the claims are intended to be embraced by the claims.