Abstract:
An air induction housing having a perforated wall which provides a first intake noise attenuation modality and further having a sound attenuation chamber interfaced with the perforated wall which provides a second intake noise attenuation modality. Multiply apertured tubes of the sound attenuation chamber provide a Helmholtz resonator, wherein the tubes are superposed the wall perforations so that, attendant to the noise attenuation, ample air entry into the air induction housing is provided. The size, number and arrangement of the perforations is selected such that ample airflow is provided and audibility of intake noise is minimized in conjunction with the corresponding tubes of the sound attenuation chamber.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to air induction housings used in the automotive arts for air intake and air filtration for supplying intake air to an internal combustion engine. More particularly, the present invention relates to an air induction housing having a perforated wall for simultaneously providing air intake and sound (acoustic) attenuation, and still more particularly, to a sound attenuation chamber having multiply apertured tubes superposed the perforations. 
       BACKGROUND OF THE INVENTION 
       [0002]    Internal combustion engines rely upon an ample source of clean air for proper combustion therewithin of the oxygen in the air mixed with a supplied fuel. In this regard, an air induction housing is provided which is connected with the intake manifold of the engine, wherein the air induction housing has at least one air induction opening for the drawing-in of air, and further has a filter disposed thereinside such that the drawn-in air must pass therethrough and thereby be cleaned prior to exiting the air induction housing on its way to the intake manifold. 
         [0003]    Problematically, a consequence of the combustion of the fuel-air mixture within the internal combustion engine is the generation of noise (i.e., unwanted sound). A component of this noise is intake noise which travels through the intake manifold, into the air induction housing, and then radiates out from the at least one air induction opening. The intake noise varies in amplitude across a wide frequency spectrum dependent upon the operational characteristics of the internal combustion engine, and to the extent that it is audible to passengers of the motor vehicle, it is undesirable. 
         [0004]    As shown at  FIG. 1 , a solution to minimize the audibility of intake noise is to equip an air induction housing  10  with an externally disposed resonator  12  connected to the air induction housing by an externally disposed snorkel  14 . The air induction housing  10  has upper and lower housing components  16 ,  18  which are sealed with respect to each other, and are also selectively separable for servicing a filter media (not shown) which is disposed thereinside. An induction duct  20  is connected to the induction housing and defines an air induction opening  22  for providing a source of intake air to the air induction housing at one side of the filtration media, as for example by being interfaced with the lower housing component  18 . An intake manifold duct  24  is adapted for connecting with the intake manifold of the internal combustion engine, and is disposed so as to direct the intake air at the other side of the filtration media out of the air induction housing  10 , as for example via the upper housing component  16 . 
         [0005]    One end of the snorkel  14  is connected to the induction duct  20  adjacent the air intake opening  22 . The other end of the snorkel  14  is connected to the resonator  12 , which is essentially an enclosed chamber. Each end of the snorkel  14  is open so that intake noise may travel between the induction duct  20  and the resonator  12 . The resonator  12  is shaped and the snorkel  14  configured (as for example as two snorkel tubes  14   a,    14   b ) such that the intake noise passing through the induction duct toward the air intake opening in part passes into the resonator and then back into the induction duct so as to attenuate the intake noise by frequency interference such that the audibility of the intake noise exiting the air intake opening is minimized. 
         [0006]    While the prior art solution to provide attenuation of intake noise does work, it does so by requiring the inclusion of an externally disposed snorkel and resonator combination which adds expense, installation complexity and packaging volume accommodation. 
         [0007]    Accordingly, what is needed is to somehow provide attenuation of intake noise as an inherent feature of the air induction housing so as to thereby minimize expense, complexity and packaging volume. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention utilizes an air induction housing having a perforated wall which provides intake noise attenuation, as is generally described in U.S. patent application Ser. No. 11/681,286, filed on Mar. 2, 2007 to Julie A. Koss and assigned to the assignee of the present invention, the entire disclosure of which patent application is hereby herein incorporated by reference, and further utilizes a sound attenuation chamber interfaced with the perforated wall which provides a second modality of intake noise attenuation, wherein multiply apertured tubes thereof are superposed the wall perforations so that, attendant to the noise attenuation, ample air entry into the air induction housing is provided. 
         [0009]    The air induction housing having a perforated sound attenuation wall and interfaced sound attenuation chamber according to the present invention includes an air induction housing having an internally disposed filtration media, and is preferably characterized by mutually selectively sealable and separable housing components; an intake manifold duct interfaced therewith adapted for connection to the intake manifold of an internal combustion engine; a perforated sound attenuation wall connected with the air induction housing and characterized by a plurality of perforations formed therein; and a sound attenuation chamber including a plurality of tubes, each tube superposed a respective perforation of the perforated wall, wherein the tubes have a plurality of apertures in the sidewalls thereof which communicate with an interior space of the sound attenuation chamber. An inner wall of the sound attenuation chamber may, itself, serve as the perforated sound attenuation wall, wherein the tubes&#39; interior openings serve as the perforations. The air induction housing may be of any configuration and is suitably shaped to suit a particular motor vehicle application. 
         [0010]    The size, number and arrangement of the perforations and the dimensional aspects of the sound attenuation chamber are selected, per the configuration of the air induction housing and the airflow requirements of the internal combustion engine, such that a multi-faceted synergy is achieved whereby: 1) ample airflow is provided through the perforations and superposed tubes to supply the internal combustion engine with required aspiration over a predetermined range of engine operation, and 2) audibility of intake noise is minimized. The multi-faceted synergy is based upon simultaneous optimization of four facets: 1) providing a plurality of perforations which collectively have an area that accommodates all anticipated airflow (aspiration) requirements of a selected internal combustion engine; 2) minimizing the diameter while simultaneously adjusting the area of the perforations such that the airflow demand of the internal combustion engine involves an airflow speed through each perforation that is below a predetermined threshold at which the perforation airflow noise generated by the flow of the air through the perforations is acceptably inaudible; 3) arranging the perforation distribution in cooperation with configuring of the air induction housing to provide a highest level of intake noise attenuation thereat (i.e., minimal audibility); and 4) further attenuating intake noise at a sound attenuation chamber by a plurality of apertures in the sidewalls of the tubes providing a Helmholtz resonator. 
         [0011]    A significant aspect of the present invention is that the intake noise attenuation is accomplished inherently by the air induction housing, itself, obviating need for any external components of any kind (as for example an external snorkel and resonator combination of the prior art). 
         [0012]    Accordingly, it is an object of the present invention to provide an air induction housing having a perforated wall which provides a first intake noise attenuation modality and having a sound attenuation chamber interfaced with the perforated wall which provides a second intake noise attenuation modality, wherein multiply apertured tubes thereof are superposed the wall perforations so that, attendant to the noise attenuation, ample air entry into the air induction housing is provided. 
         [0013]    This and additional objects, features and advantages of the present invention will become clearer from the following specification of a preferred embodiment. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a perspective view of a prior art air induction housing including an external snorkel and resonator combination for attenuating intake noise. 
           [0015]      FIG. 2A  is a graphical representation of two acoustic (sound) waves 180 degrees out of phase with respect to each other such that the acoustic waves are in destructive interference. 
           [0016]      FIG. 2B  is a schematic representation of how sound attenuation is believed to be provided by an air induction housing having a perforated sound attenuation wall according to the present invention. 
           [0017]      FIG. 3  is a perspective view of an example of an air induction housing according to the present invention. 
           [0018]      FIG. 4  is a sectional view, seen along line  4 - 4  of  FIG. 3 , showing in particular an example of a sound attenuation chamber according to the present invention. 
           [0019]      FIG. 5  is a sectional view of a tube of the sound attenuation chamber, seen along line  5 - 5  of  FIG. 4 . 
           [0020]      FIG. 6  is a sectional view, seen along line  6 - 6  of  FIG. 5 . 
           [0021]      FIG. 7  is a graph of engine RPM versus sound level, wherein a first plot is for a source of noise, a second plot is for attenuation of the noise of the first plot by a prior art air induction housing, and a third plot is for attenuation of the noise of the first plot by air induction housing according to the present invention. 
           [0022]      FIG. 8  is a graph of engine RPM versus sound level for several air induction housings according to the present invention each having a selected perforated sound attenuating wall but not including a sound attenuation chamber; for a prior art air induction housing with external snorkel and resonator combination per  FIG. 1 ; and for an exemplar base line. 
           [0023]      FIG. 9  is a graph of airflow rate versus air pressure loss for a prior art air induction housing with external snorkel and resonator combination per  FIG. 1 , and for an air induction housing having a perforated sound attenuating wall according to the present invention but not including a sound attenuation chamber. 
           [0024]      FIG. 10  is a flow chart of an algorithm for optimizing acoustic attenuation of intake noise by the air induction housing according to the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0025]    Referring now to the Drawing,  FIGS. 2A through 10  depict various aspects of an air induction housing having a perforated sound attenuation wall and interfacing sound attenuation chamber according to the present invention. 
         [0026]      FIGS. 2A and 2B  show principles of physics under which it is believed an air induction housing having a perforated sound attenuation wall according to the present invention provides acoustic (sound) attenuation of intake noise, without resort to an external snorkel and resonator combination as used in the prior art. 
         [0027]      FIG. 2A  demonstrates the principle of destructive interference of acoustic (sound) waves. In this case, acoustic wave A is 180 degrees out of phase with acoustic wave B. As a result, if acoustic waves A and B have the same amplitude, then they completely cancel one another by destructive interference, the result being line C of zero amplitude. 
         [0028]    Turning attention next to  FIG. 2B , a schematic representation of air induction housing having a perforated sound attenuating wall  100  according to the present invention is depicted, including an air induction housing  102 , an intake manifold duct  108  and a perforated wall  110  having a plurality of perforations  112  (holes or apertures) formed therein. Operationally, intake noise N from the engine passes into the air induction housing  102  via the intake manifold duct  108 , enters into the interior space  114  of the air induction housing passing through a filtration media  116  disposed within the air induction housing, and strikes the perforated wall  110 . The noise N strikes the perforated wall as an incident acoustic wave Ni, and is reflected as a reflected acoustic wave Nr which is 180 degrees out of phase with respect to the incident acoustic wave, whereby the incident and reflected acoustic waves mutually undergo destructive interference. 
         [0029]    Further, under another principle, it is believed that to the extent the diameter D of the perforations  112  is less than any acoustic wave length X of the noise (see  FIG. 2A ), then these acoustic waves cannot exit the perforations. Accordingly, the level of sound emitted from the perforations exterior to the air induction housing  100  is acceptably inaudible to the occupants of the motor vehicle. 
         [0030]    A mathematical theory believed to describe the foregoing description is as follows. 
         [0031]    A reflection coefficient, R, is used to describe the ratio of the reflected wave to that of the incident wave (see  Acoustics of Ducts and Mufflers with Application to Exhaust and Ventilation System Design,  by M. L. Munjal, published by John Wiley &amp; Sons, 1987): 
         [0000]      R≡|R|e jθ ,   (1) 
         [0000]    where |R| and θ are the amplitude and phase of the reflection coefficient, respectively. 
         [0032]    The amplitude and phase of the reflection coefficient at an opening, i.e., the perforations, is described by the following equations: 
         [0000]      |R|≅1−0.14k o   2 r o   2    (2) 
         [0000]      θ=π−tan −1 (1.2 k   o   r   o ),   (3) 
         [0000]    where k o  is an initial wave number in a non-viscous fluid (i.e., air) and r o  is the radius of the enclosure (i.e., the air induction housing, itself). 
         [0033]    From equations (2) and (3), it is determined that the perforations of the perforated wall reflect the incident acoustic wave (of the engine intake noise) almost fully but with opposite phase as a reflected acoustic wave. Therefore, very little sound is emitted from the perforations because the reflected acoustic wave and subsequent incoming acoustic wave cancel one another by destructive interference. 
         [0034]    Further, given a diameter, D, of the perforations, and given a smallest acoustic wave length, λ min , of the vast majority of the noise N, to the extent that D&lt;λ min , all the acoustic waves having λ satisfying λ min &lt;λ cannot exit the perforations. Accordingly, a minimum perforation diameter, D, is preferred. 
         [0035]    However, a minimum diameter, D, of the perforations can produce noise as the airflow swiftly passes therethrough, as for example audibly detected as a howl, hiss or whistle. It is preferable that the Mach number, M, through the perforations be less than about 0.125, where M is defined by: 
         [0000]        M=v/s,    (4) 
         [0000]    where s is the speed of sound in air and v is defined by: 
         [0000]        v =Ψ/(ρ A   P ),   (5) 
         [0000]    where Ψ is the maximum intake air mass flow rate of an internal combustion engine operational range divided by the number of perforations, ρ is the density of air, and A P  is the area of each perforation. 
         [0036]    With regard to intake noise attenuation provided by the sound attenuation chamber, the attenuation operates on the basis of a Helmholtz resonator, as for example discussed in U.S. Pat. No. 5,979,598, wherein the resonant frequency (see http://en.wikipedia.org/wiki/Helmholtz_resonator) is: 
         [0000]    
       
         
           
             
               
                 
                   
                     ω 
                     H 
                   
                   = 
                   
                     
                       γ 
                        
                       
                           
                       
                        
                       
                         
                           A 
                           2 
                         
                         m 
                       
                        
                       
                         
                           P 
                           0 
                         
                         
                           V 
                           0 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   6 
                   ) 
                 
               
             
           
         
       
     
         [0000]    where γ is the adiabatic index, A is the cross-sectional area of an aperture (or neck in a classic Helmholtz resonator), m is the mass of the gas in the cavity, P 0  is the static pressure in the cavity, V 0  is the static volume of the cavity. 
         [0037]    Referring now to  FIGS. 3 through 6 , an exemplary configuration of an air induction housing with a perforated sound attenuating wall and interfaced sound attenuation chamber  100 ′ is depicted. 
         [0038]    The air induction housing  102 ′ has upper and lower housing components  104 ,  106  which are selectively sealable and separable with respect to each other (as for example via peripherally disposed clips) for servicing a filter media (not shown, but indicated at  FIG. 2B ) which is disposed thereinside. An intake manifold duct  108 ′ is adapted for connecting with the intake manifold of an internal combustion engine, and its connection with the air induction housing is disposed downstream of the filtration media such that the intake air passing through the filtration media subsequently passes out of the air induction housing  102 ′, as for example via the upper housing component  104 . 
         [0039]    A sound attenuation chamber  120  is connected with the air induction housing, wherein a perforated wall  110 ′ is interfaced with the sound attenuation chamber such that each of the perforations  112 ′ thereof are superposed a respective tube  122 , wherein the tubes and the perforations collectively define an air induction opening for providing a source of intake air A′ to the air induction housing  102 ′ at the upstream side of the filtration media, as for example by being interfaced with the lower housing component  106 . By way of exemplification shown at  FIG. 4 , the inner wall  122   a  of the sound attenuation chamber  120  serves as the perforated wall  110 ′, and the sound attenuation chamber is fitted into a receiving opening  102   a  of the induction housing  102 , being sealed therein by for example a resilient seal or gasket  124 , and secured in place with respect to the induction housing, as for example by fasteners  126 . The inner opening of the central passage  134  of each tube serves as the perforation  112 ′ in the exemplification of  FIG. 4 . 
         [0040]    The sound attenuation chamber  120  is composed of an internal space  128  with air A″ thereinside, wherein the tubes  122  pass through the internal space. The sidewalls  130  of the tubes  122  are each provided with a plurality of apertures  132 , wherein the apertures communicate between the central passage  134  of each tube (each central passage being superposed its respective perforation  112 ′) and the internal space  128 , wherein the internal space is sealed except for the apertures. Optionally, baffling  136  (shown in phantom merely in exemplar fashion at one location), may be located within the internal space  128  of the sound attenuation chamber  120 , wherein the number, shapes and locations of the baffles of the baffling are selected to tune the resonations N 2 R, as depicted at  FIG. 6  (discussed immediately below). 
         [0041]    In operation, as shown at  FIG. 4 , most noise N 1  from a source of noise downstream of the filtration media is reflected at the perforated wall  110 ′, in the manner as exemplified by  FIG. 2B . What portion of noise N 2  which passes into the central passage  134  of any of the tubes  122  interacts with the mass of air A″ within the internal space  128  in the manner of a Helmholtz resonator (see also  FIG. 6 ), such that the resonations N 2 R of the portion of noise N 2  with the chamber air A″ causes dissipation of the noise N 2  progressively along the tubes  122 , whereupon very little noise from the source downstream of the filtration media passes out of the tubes external to the air induction housing  102 ′. 
         [0042]    Turning attention to  FIG. 7 , a graph  140  of engine RPM versus emitted sound level of intake noise is shown. Plot  142  represents a noise source from a four cylinder internal combustion engine. Plot  144  is for the sound emitted by a prior art air induction housing with snorkel and resonator, analogous to that of  FIG. 1 , wherein total system volume is 10.35 L, air intake housing lower component volume is 6 L, air intake housing upper component volume is 2.55 L, total inlet area is about 5,000 mm 2  via an 80 mm diameter snorkel. Plot  146  is for the sound emitted by an air induction housing with perforated sound attenuating wall and sound attenuation chamber according to the present invention analogous to that of  FIG. 3 , wherein total system volume is 10.1 L, sound attenuation chamber volume is 0.9 L, air intake housing lower component volume is 5.07 L, air intake housing upper component volume is 2.55 L, total inlet area is about 5,000 mm 2  via 63 perforations (63 tubes) each perforation (central passage) is 5 mm in diameter, each tube is 50 mm long, and has 5 apertures, each aperture being 1 mm in diameter. Plot  148  represents a baseline requirement for sound attenuation. 
         [0043]    Turning attention to  FIG. 8 , a graph  150  of engine RPM versus emitted sound level of intake noise is shown. Plot  152  is a baseline requirement for sound emission. Plot  154  is the sound emitted by a prior art air induction housing with snorkel and resonator, as per that of  FIG. 1 . Plots  156 ,  158 ,  160 , and  162  are for an air induction housing with perforated sound attenuating wall according to the present invention (for example, analogous to  FIG. 3  but absent a sound attenuation chamber), wherein plot  156  is for 10 circular perforations each of 27.5 mm diameter, plot  158  is for  103  circular perforations each of 10 mm diameter, plot  160  is for 200 circular perforations each of 7.2 mm diameter and plot  162  is for 10,000 circular perforations each of 1.02 mm diameter. It is seen that the present invention provides low sound level emission, in each plot better than the prior art, and better than the base line requirement. Further the best result is seen to be provided with the smallest diameter perforations. 
         [0044]    Turning attention next to  FIG. 9 , a graph  170  of airflow rate versus air pressure loss is shown. Plot  172  is for a prior art air induction housing with snorkel and resonator as per that of  FIG. 1 , and plot  174  is for an air induction housing with perforated sound attenuating wall according to the present invention (for example, analogous to  FIG. 3  but absent a sound attenuation chamber), having  73  perforations. It will be seen the results are comparable, whereby it is interpreted that the present invention provides air pass-through that is better than the prior art. 
         [0045]    Table I shows data taken for perforated walls according to the present invention (without a sound attenuation chamber) for various internal combustion engines, various selected perforation numbers and diameters for each engine, and the resulting Mach numbers associated with each of the perforation diameters and numbers selected. 
         [0000]    
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE I 
               
               
                   
               
               
                   
                 Inlet area (mm 2 ) 
                 Perforation 
                 Number of 
                   
                   
               
               
                 Engine Type 
                 (per best practice) 
                 diameter (mm) 
                 perforations 
                 Flow Rate (g/s) 
                 Mach Number 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 4 cylinder 
                 2968 
                 5 
                 152 
                 140 
                 0.111 
               
               
                   
                   
                 10 
                 38 
                   
                 0.111 
               
               
                   
                   
                 15 
                 17 
                   
                 0.111 
               
               
                   
                   
                 20 
                 10 
                   
                 0.106 
               
               
                   
                   
                 30 
                 5 
                   
                 0.094 
               
               
                   
                   
                 40 
                 3 
                   
                 0.088 
               
               
                   
                   
                 50 
                 2 
                   
                 0.085 
               
               
                 6 cylinder 
                 5959 
                 5 
                 304 
                 240 
                 0.095 
               
               
                   
                   
                 10 
                 76 
                   
                 0.095 
               
               
                   
                   
                 15 
                 34 
                   
                 0.095 
               
               
                   
                   
                 20 
                 19 
                   
                 0.096 
               
               
                   
                   
                 30 
                 9 
                   
                 0.090 
               
               
                   
                   
                 40 
                 5 
                   
                 0.091 
               
               
                   
                   
                 50 
                 3 
                   
                 0.096 
               
               
                 8 cylinder 
                 8247 
                 5 
                 420 
                 300 
                 0.086 
               
               
                   
                   
                 10 
                 105 
                   
                 0.086 
               
               
                   
                   
                 15 
                 47 
                   
                 0.086 
               
               
                   
                   
                 20 
                 27 
                   
                 0.084 
               
               
                   
                   
                 30 
                 12 
                   
                 0.084 
               
               
                   
                   
                 40 
                 7 
                   
                 0.081 
               
               
                   
                   
                 50 
                 5 
                   
                 0.073 
               
               
                 8 cylinder high 
                 8247 
                 5 
                 420 
                 450 
                 0.129 
               
               
                 performance engine 
                   
                 10 
                 105 
                   
                 0.129 
               
               
                   
                   
                 15 
                 47 
                   
                 0.129 
               
               
                   
                   
                 20 
                 27 
                   
                 0.126 
               
               
                   
                   
                 30 
                 12 
                   
                 0.126 
               
               
                   
                   
                 40 
                 7 
                   
                 0.121 
               
               
                   
                   
                 50 
                 5 
                   
                 0.109 
               
               
                   
               
             
          
         
       
     
         [0046]    It is seen from Table I that a wide range of perforation diameters can achieve a desired small Mach number. It is to be further noted that, per the above theoretical discussion, for purposes of acoustic (sound) attenuation, the smaller the perforation diameter the better. However, as mentioned hereinabove, it is necessary to adjust the area of the perforations so that the airflow (more specifically, the maximum airflow demanded of the internal combustion engine) passing through the perforations does not, itself, create undesirable noise, wherein it is preferred that the Mach number be under about 0.125 in order to achieve this result. 
         [0047]    Thus, from Table I, it is possible to find best perforation parameters (by “best” is meant relative to the test results summarized in Table I, in that other tests may provide other “best” results): for the four cylinder engine is a perforated wall having  152  perforations of 5 mm diameter and having a Mach number equal to 0.111, best for the six cylinder engine is a perforated wall having  304  perforations of 5 mm diameter and having a Mach number equal to 0.095, best for the eight cylinder engine is a perforated wall having  420  perforations of 5 mm diameter and having a Mach number equal to 0.086. The best for the high performance eight cylinder engine may be a perforated wall having  420  perforations of 5 mm diameter and having a Mach number equal to 0.129, in that a Mach number of 0.129 may be acceptable (as empirically ascertained) in that engine application. 
         [0048]    Turning attention now to  FIG. 10 , depicted are the steps associated with an algorithm  200  for expositing a method for optimizing the air induction housing with a sound attenuating perforated wall and interfaced sound attenuation chamber according to the present invention. 
         [0049]    At Block  202 , the algorithm is initialized. At Block  204 , the engine airflow rate requirement of a selected internal combustion engine is determined. At Block  206 , the necessary inlet area, A I , is determined such that back pressure is not an issue for the operation of the internal combustion engine, per the determination at Block  204 . Once this area is determined, preferably about one percent (1%) is added thereto in order to account for entrance/exit airflow losses. This inlet area is the starting point for determining the number of perforations (based on average perforation area) of the perforated wall of the air induction housing. 
         [0050]    Next, at Block  208 , a minimum perforation diameter is selected using an empirical best estimation to provide a perforation area, A P . Next, at Block  210 , the number, n, of perforations is calculated, wherein n=A I /A P . The smaller the perforation diameter, the better the noise attenuation benefit, as there are more waves reflected back into the box, as discussed hereinabove. However, the minimum area (and therefore diameter) of the perforations is limited by the Mach number, M, of the airflow through the perforations when at the maximum airflow rate, as discussed hereinabove. 
         [0051]    Next, at Block  212 , the Mach number, M, for the airflow through the perforations when at the maximum mass flow rate is calculated using, for example, equations (4) and (5). At Decision Block  214 , inquiry is made whether the Mach number is less than, by way of preference, about 0.125. If the answer to the inquiry is no, then the algorithm returns to Block  208 , whereat a new minimum perforation diameter is selected, larger than that previously selected (that is, assuming the first chosen minimum diameter was a true minimum, otherwise various larger and smaller diameters can be tried to find the minimum). However, if the answer to the inquiry is yes, then the algorithm advances to Block  216 . 
         [0052]    At Block  216 , the configuration of the air induction housing is determined. In so doing, taken into account are the packaging requirements for accommodation within the engine compartment, as well as a best estimation for providing acoustic attenuation, for example, per equations (2) and (3). The shape may be any suitable and/or necessary shape, as for example an irregular polygonal shape, a regular polygonal shape, spherical shape, cylindrical shape, pyramidular shape, or some combinational shape thereof, etc. Next, at Block  218 , a distribution of the perforations is selected based upon an empirical best estimate. The spacing between the perforations should be maximized to ensure the best possible wave reflection (and thus sound attenuation). The spacing between the perforations is limited by the air induction housing size, per the number of perforations and the perforation area. 
         [0053]    Next, at Decision Block  220 , inquiry is made, for example by use of empirical testing of a modeled air induction housing, whether the sound attenuation is a maximum (i.e., sound emission at the perforations is a minimum). If the answer to the inquiry is no, then the algorithm returns to Block  218 , wherein any possible reconfiguration of the air induction housing is made (if packaging constraints allow), and the perforation distribution is again reselected. However, if the answer to the inquiry at Decision Block  220  is yes, then the algorithm advances to Block  222 . 
         [0054]    At Block  222 , the configuration of the sound attenuation chamber is determined. In so doing, taken into account are the packaging requirements for accommodation within the engine compartment, as well as a best estimation for providing acoustic attenuation via Helmholtz resonation through the tubes, for example, per equation (6). For example, the shape may be any suitable and/or necessary shape, wherein a resonation tuned internal space volume (of the sound attenuation chamber) is selectively provided, and the length of the tubes and number and size of the apertures formed in the sidewalls thereof, and internal space baffling, are all selected based upon resonational dissipation, at least in part, for example, equation (6), so that intake noise is attenuated by resonating with the air within the interior space of the sound attenuation chamber. The algorithm then advances to Decision Block  224 . 
         [0055]    At Decision Block  224 , inquiry is made whether the amount of sound attenuation is acceptable based upon a predetermined base line (as for example plot  148  of  FIG. 7 , or plot  152  of  FIG. 8 ). If the answer to the inquiry is no, then the algorithm returns to Block  216  to continue optimization of sound attenuation. However, if the answer to the inquiry at Decision Block  224  is yes, then fabrication of an air induction housing with a sound attenuating perforated wall according to the present invention may be performed with confidence. 
         [0056]    It is to be understood that the perforations may have any shape or differing shapes, any area or differing areas, any diameter or differing diameters, and have uniform or non-uniform spacing therebetween, the sound attenuation chamber may be located anywhere or generally everywhere of the air induction housing, and that multiple layers of the perforated wall may be utilized, all for the purpose of tuning the intake noise emitted from the air induction system to a desired level of attenuation (acceptably inaudible) at the perforations. 
         [0057]    To those skilled in the art to which this invention appertains, the above described preferred embodiment may be subject to change or modification. Such change or modification can be carried out without departing from the scope of the invention, which is intended to be limited only by the scope of the appended claims.