Abstract:
The present invention relates to a motor vehicle mounted directional microphone assembly for use in hands-free cellular telecommunications. The microphone assembly is comprised of a case and a removable directional microphone module. The case is adapted to mount and lock the module in a plurality of different orientations, thereby enabling the assembly to accommodate various mounting arrangements within the vehicle. The module is releasable, however, from its locked position to permit re-orientation of the microphone with respect to the case, if desired. The module is also completely removable from the case to permit mounting of the module within the vehicle in mounting arrangements independent of the case.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation-in-part of U.S. provisional application Ser. No. 60/106,480 filed Oct. 30, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     Cellular telephones are widely used in motor vehicle environments. The use of traditional hand-held telephones in such environments, however, is often distracting to a driver and hinders the driver&#39;s ability to maneuver in traffic. Hand-held telephones, therefore, increase the risk of accident. 
     As a result, some motor vehicle and cellular telephone manufacturers have developed systems enabling hands-free telephone operation. Such hands-free telephone systems often employ a microphone that is mounted within the vehicle and is used to pick up speech for telephone communication and voice commands. The microphone in such systems is often coupled to a radio/telephone system located within the vehicle. The radio/telephone system generally comprises a traditional cellular telephone system that is coupled to a vehicle radio in such manner to enable the use of the radio amplifier and speakers for listening to incoming telephone audio. The telephone/radio system also provides power to, and receives electrical voice signals from, the microphone. 
     In operation, a driver typically presses a button on the radio or on the microphone to establish hands-free use. The driver is then able to listen to a caller&#39;s voice via the radio speakers and speak freely without being required to manipulate or hold a telephone. The driver&#39;s speech is transduced to electrical signals by the microphone, which electrical signals are transferred to the radio/telephone system and then to the caller via the vehicle cellular telephone system. 
     A number of different microphone assemblies have been developed for such hands-free motor vehicle applications. For example, omnidirectional microphone assemblies have been mounted on interior surfaces of automobiles, typically in two locations—at a forward, central headliner position and at or near the top of the driver side roof support pillar (A-pillar). By their nature, however, omnidirectional microphones pick up sound from all directions, and thus their performance in motor vehicle applications often suffers due to the numerous non-speaker noise sources in the vehicle, such as, for example, the ventilation system, the defroster, other people speaking, etc. 
     Directional microphones have also been developed for motor vehicle applications, and can produce significant performance advantages over omnidirectional microphones. A typical prior art directional microphone assembly is illustrated in FIG. 1. A microphone  1  is mounted behind a surface  3 , which may form part of a mostly acoustically opaque housing or a mostly acoustically transparent grill cover. The front of the element diaphragm is acoustically coupled through tube  5  and surface inlet  7  to the acoustic pick-up region  9 . Similarly, the rear of the diaphragm is acoustically coupled through tube  11  and surface inlet  13  to the acoustic pick-up region  9 . Tubes  5  and  11  are narrow, generally cylindrical and substantially resonant over the desired frequency range. Acoustic resistor  15  in tube  11  and the enclosed rear volume  17  behind the diaphragm, form a low-pass filter/delay for sound entering surface hole  13 . This delay, along with the dimensions of tubes  5  and  11  and the distance between surface inlets  7  and  13 , forms a first-order directional pickup pattern in the pick-up region  9  that is directed along a line from surface inlet  13  to surface inlet  7 . 
     Thus, because of the directivity of the pickup, directional microphones generally require that much greater skill and care be used in positioning the microphone within a motor vehicle in order to achieve the aforementioned performance advantages over omnidirectional microphones. Like omnidirectional microphones, directional microphones have also typically been positioned at a forward central headliner location and at or near the top of the A-pillar in motor vehicle applications. Unlike omnidirectional microphones, however, if a directional microphone is improperly installed in those locations, the performance of the microphone can be adversely affected. Similarly, if a directional microphone designed for those locations is installed in another location for which the microphone is not suited, or if the microphone position is modified by the consumer, the performance may also suffer. 
     It is desirable, therefore, that a microphone assembly design address these installation concerns to maximize directional microphone performance without requiring that an acoustic expert be involved in the installation of the microphone. In addition, it is also desirable that any such design be adaptable to enable flush mounting with any number of existing surfaces in the vehicle, if the vehicle manufacture requires such mounting for aesthetic reasons. 
     Consequently, it is an object of the present invention to provide a microphone assembly that can easily and properly be installed at the typical headliner and A-pillar locations as well as any number of other locations in the vehicle, and that can accommodate both left and right drive vehicles. 
     It is another object of the present invention to provide a microphone assembly that can be easily modified for proper installation at different locations but is not easily disturbed by a consumer. 
     It is a further object of the present invention to provide a microphone assembly that can easily be adapted for flush mounting with any number of surfaces within the vehicle. 
     BRIEF SUMMARY OF THE INVENTION 
     These and other objects of the invention are achieved in a directional microphone assembly having a case and a removable directional microphone module. The case is adapted to mount and lock the module in place thereon in a plurality of different orientations. The directional microphone module is removable from the case and may be re-oriented thereon to accommodate different desired mounting arrangements. 
     The removable directional microphone module is comprised of a directional microphone element having front and rear inlet ports that are acoustically coupled to front and rear inlet paths, respectively. Sound from a pickup region enters the front and rear inlet paths and is coupled via the front and rear inlet ports to front and rear microphone chambers defined in part by a microphone diaphragm. 
     In one embodiment, front and rear acoustic plugs are located in the front and rear sound inlet paths. The front and rear acoustic plugs are, for example, made of sintered porous plastic or open cell acoustic foam material. A windscreen made of a cloth or screen material may also be located over the acoustic plugs. The windscreen and acoustic plugs generally operate together to protect against dirt, dust, moisture, etc. and cut down on wind noises. 
     In another embodiment, the front and rear inlet paths are generally non-cylindrical in shape. The inlet paths are substantially non-resonant in a frequency range of desired sound pickup. 
     In a further embodiment, the removable directional microphone module includes a housing. The microphone element is mounted in the housing, and the front and rear sound inlet paths are formed in the housing. Recesses in the housing receive the front and rear acoustic plugs such that the front and rear acoustic plugs are located, respectively, in the front and rear inlet paths. The acoustic plugs may, when inserted in the recesses, form portions of a top surface of the housing. A windscreen then may be attached to the top surface of the housing. 
     In a still further embodiment, the case includes at least one mounting surface and a plurality of index notches. The removable directional microphone module likewise includes at least one index tab. When the module is mounted on the mating surface, the index tab engages one of the index notches, depending on the desired orientation of the microphone. The module is then “locked” in the selected orientation, but releasable therefrom. The index notches may, for example, be equally spaced at every 30° around the mounting surface, thereby enabling flexible orientation of the microphone within the case. The module is also removable from its mounted relationship with the case to enable re-orientation of the microphone and/or support different mounting arrangements. 
    
    
     These and other advantages and novel features of the present invention, as well as details of an illustrated embodiment thereof, will be more fully understood from the following description and drawings. 
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     FIG. 1 illustrates a typical prior art directional microphone assembly. 
     FIG. 2 a  illustrates a front view of a microphone assembly built in accordance with the present invention for headliner mounting in a left drive vehicle. 
     FIG. 2 b  illustrates a side view of the microphone assembly of FIG. 2 a.    
     FIG. 2 c  illustrates a rear view of the microphone assembly of FIG. 2 a.    
     FIG. 3 a  illustrates a front view of a microphone assembly built in accordance with the present invention for A-pillar mounting in a left drive vehicle. 
     FIG. 3 b  illustrates a side view of the microphone assembly of FIG. 3 a.    
     FIG. 3 c  illustrates a rear view of the microphone assembly of FIG. 3 a.    
     FIG. 4 a  illustrates a bracket design for A-pillar mounting in accordance with the present invention. 
     FIG. 4 b  illustrates a bracket design for headliner mounting in accordance with the present invention. 
     FIGS. 5 a  and  5   b  illustrate one embodiment of a bracket mounting and release arrangement in accordance with the present invention. 
     FIGS. 6 a  and  6   b  illustrate another embodiment of a bracket mounting and release arrangement in accordance with the present invention. 
     FIG. 7 a  illustrates an inside view of a base portion of a case built for headliner mounting in accordance with the present invention. 
     FIG. 7 b  is a cross-sectional view of the base of FIG. 7 a  taken along lines B—B. 
     FIG. 8 a  illustrates an inside view of a cover portion of the case built for headliner mounting in accordance with the present invention. 
     FIG. 8 b  is a cross-sectional view of the cover of FIG. 8 a  taken along lines A—A. 
     FIG. 9 a  illustrates an inside view of a base portion of a case built for A-pillar mounting in accordance with the present invention. 
     FIG. 9 b  is a cross-sectional view of the base of FIG. 9 a  taken along lines B—B. 
     FIG. 10 a  illustrates an inside view of a cover portion of the case built for A-pillar mounting in accordance with the present invention. 
     FIG. 10 b  is a cross sectional view of the cover of FIG. 10 a  taken along lines A—A. 
     FIG. 11 a  is a top view of the microphone module of the present invention. 
     FIG. 11 b  is a side cross sectional view of the module taken along lines A—A of FIG. 11 a.    
     FIG. 11 c  is a bottom view of the microphone module of the present invention. 
     FIG. 12 illustrates a bottom surface of a windscreen that seats on a top surface of the microphone module of the present invention. 
     FIG. 13 is an exploded view of the microphone module of the present invention. 
     FIGS. 14 a  and  14   b  illustrate an alternate embodiment of the cover and removable module of the directional microphone assembly of the present invention. 
     FIG. 15 is a top view of the cover of the alternate embodiment. 
     FIG. 16 illustrates a windscreen built in accordance with the alternate embodiment. 
     FIG. 17 illustrates a partial cross-sectional view of the cover and removable module of FIGS. 14 a  and  14   b.    
     FIG. 18 illustrates the removable module of the alternate embodiment removed from the cover. 
     FIG. 19 illustrates the inside of the cover with the removable module removed therefrom. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 2 a ,  2   b  and  2   c  illustrate front, side and rear views, respectively, of a microphone assembly  21  of the present invention for headliner mounting in a left drive vehicle. Microphone assembly  21  includes a case  23  and a mounting bracket  25 . The case  23  has a grill portion  31 , behind which sound inlet ports  33  and  35  are located. As explained more completely below, sound inlet ports  33  and  35  acoustically couple sound to a microphone element (not shown) located within the case  23 . A cable  27  electrically connects the microphone element to a radio/telephone system located within the vehicle. A button switch  29  is used to initiate or end a telephone call. 
     The case  23  is mounted generally at a forward, center headliner location in a vehicle approximately near the rear view mirror. The headliner, as understood in the automotive industry, is the material that is attached to the inner metal ceiling of the vehicle. For aesthetic and practical mounting considerations, it is desirable to keep the case  23  at one mounting position (horizontally straight back) and to keep the switch  29  at the back of the case  23  (i.e., closer to the driver). The bracket  25  is therefore designed to be inserted underneath the headliner so that the case  23  rests on the outer surface of the headliner material. In other words, when the assembly  21  is installed, the headliner is located between the bracket  25  and the case  23 , and the case  23  rests on the ceiling of the car. The bracket  25 , being generally straight, enables the microphone assembly  21  to be maintained in a horizontally straight back position when the microphone assembly  21  is firmly installed (i.e., when the headliner contacts a surface  37  of the bracket  25 ). 
     For such headliner mounting, however, we have determined that the optimum acoustical orientation of the microphone is horizontally straight back, but with a slight angling of approximately 30° towards the driver location. Such angling enables driver voice pickup (the driver generally sits farther forward than the passenger) while still enabling passenger voice pickup. To achieve such angling while maintaining the horizontally straight back positioning of the case, sound inlet ports  33  and  35  are oriented approximately 30° off the horizontally straight back axis as seen in FIG. 2 a . Sound inlet port direction of maximum sensitivity is shown generally by arrow  39 . 
     FIGS. 3 a ,  3   b  and  3   c  illustrate front, side and rear views, respectively, of a microphone assembly  41  of the present invention for A-pillar mounting in a left drive car. The microphone assembly  21  is virtually identical to the microphone assembly  21  of FIG. 2, except for bracket  43  and the orientation of the sound inlet ports  33  and  35 . In this embodiment, the case  23  is mounted at or near the top of the vehicle driver A-pillar. The A-pillar, as understood in.the automotive industry, is the windshield roof support pillar. In the interior of the vehicle, the A-pillar is typically covered by a plastic piece, much like the metal roof is covered by the headliner material. For aesthetic and practical mounting considerations, it is similarly desirable to keep the case  23  at one mounting position (in-line with the A-pillar) and to keep the switch  29  at the bottom of the case (i.e., closer to the driver). Aligning the case  23  with the A-pillar results in a more stable mounting. If the case  23  were mounted so that it cut across the A-pillar then the case  23  could rock back and forth, resulting in a degradation of performance. The bracket  43  is therefore designed to be inserted underneath the plastic piece mounted on the A-pillar so that the case  23  rests on the outer surface of that plastic piece. In other words, when the assembly  41  is installed, the A-pillar plastic piece is located between the bracket  43  and the case  23 , and the case  23  rests on the A-pillar support. The bracket  43  is angled at a 45° angle to the case  23  (see FIG. 3 c ) to maintain the case aligned with the A-pillar when the microphone assembly  41  is firmly installed (i.e., when the A-pillar plastic piece contacts a surface  45  of the bracket  43 ). 
     For such A-pillar mounting, we have determined that the optimum acoustical orientation of the microphone is horizontally straight back. Such orientation provides the best compromise between driver speech pickup and dashboard noise (e.g., from the ventilation system, the defroster, the audio speakers, etc.). The combination of the 45° angle of the bracket and a 30° off-axis orientation of the sound inlet ports (see FIG. 3 a ) closely approximates the desired horizontally straight back acoustical orientation. However, as can be seen in FIG. 3 a , the sound inlet ports are rotated 180° from their location in FIG. 2 a , such that sound inlet port direction is now shown by arrow  47 . 
     Thus as is apparent, different clips are used to establish and maintain proper alignment for both mounting locations while using essentially the same microphone. FIGS. 4 a  and  4   b  illustrate brackets  25  and  43  of FIGS. 2 a - 2   c  and FIGS. 3 a - 3   c , respectively. Bracket  25 , as mentioned above, is generally straight. Bracket  43  is formed at a 135° angle as shown so that the bracket  43  maintains a 45° angle to the case  23  as shown in FIG. 3 c . As discussed more completely below, clips  25  and  43  are interchangeable and can be used with the same microphone assembly case. 
     FIGS. 5 a  and  5   b  illustrate one embodiment of a bracket mounting and release arrangement in accordance with the present invention. FIG. 5 a  illustrates the rear of case  23  with clip  25  disassembled therefrom. FIG. 5 b  illustrates a side cross sectional view of the bracket  25  in a mounted position on the case. For assembly, an end  45  of bracket  25  is placed in a recess  47  of case  23 . The bracket  25  is then rotated down in a direction of arrow  49  in FIG. 5 b . A retaining member  51  mates with an opening  53  in the bracket  25  until a portion of the bracket  25  adjacent the opening  53  is received under a surface  55  of the retaining member  51 , as shown in FIG. 5 b  by an arrow  57 . The retaining member  51  is moveable and performs a spring type retaining function in that the bracket  25  is “snapped” into place onto the case  23  when the bracket  25  portion becomes engaged under the surface  55  of the retaining member  51 . 
     The retaining member  51  is also releasable, permitting the bracket  25  to be easily removed from the case  23  by movement of the retaining member  51  and release of the bracket  25  portion from engagement under the surface  55  of the retaining member  51 . Bracket  43  may also be mounted on the case  23  and released therefrom in the same manner discussed above with respect to bracket  25 . 
     FIGS. 6 a  and  6   b  illustrate another embodiment of a bracket mounting arrangement in accordance with the present invention. FIG. 6 a  illustrates a mounting sleeve  59  that is located on the rear of case  23  with bracket  25  disassembled from the sleeve  59 . FIG. 6 b  illustrates a side cross sectional view of bracket  25  inserted into the sleeve  59  and in an assembled position on the case  23 . During assembly, an end  61  of the bracket  25  is inserted in a horizontal direction into the sleeve  59 . A retaining member  63  becomes depressed as it enters the sleeve  59 , enabling the end  61  of the bracket  25  to be moved toward an end  69  of the sleeve  59 . The retaining member  63  regains its pre-assembled shape when it enters a recess  65  in the sleeve  59 . In that position, a wall  67  that defines a portion of the recess  65  acts as a mechanical stop to prevent the bracket  25  from being removed from the sleeve  59  by virtue of the engagement of retaining member  63  against the wall  67 . Like the embodiment of FIGS. 5 a  and  5   b , the retaining member  63  is also movable and similarly performs a spring-type retaining function in that the bracket  25  is snapped into place onto the case  23  when the retaining member  63  regains its preassembled shape upon entering the recess  65 . 
     The retaining member  63  is also, like the embodiment of FIGS. 5 a  and  5   b , releasable. In this embodiment, however, the bracket  25  is removed from the sleeve  59  (and thus the case  23 ) by manipulation of tool  71 . More specifically, a hook end  73  of tool  71  is used to engage a recess  75  on retaining member  63 . The retaining member  63  is then pulled down so that it can clear wall  67 , and the bracket  25  can be removed by pulling it in a horizontal direction out of the sleeve  59 . Again, bracket  43  may also be mounted on case  23  and released therefrom in the same manner discussed immediately above with respect to bracket  25 . 
     As can be best seen in FIGS. 2 b  and  3   b , case  23  is comprised of a base  77  and a cover  79 . FIG. 7 a  illustrates an inside view of base  77  of case  23  for microphone assembly  21 . FIG. 7 b  is a cross sectional view of the base  77  taken along lines B—B of FIG. 7 a . As can be seen, base  77  has bracket  25  in a mounted position thereon. A printed circuit board  81  is mounted on the inside of base  77  and electrically connects a microphone element (not shown) to the radio/telephone system of the vehicle via cable  27 , as discussed above. The base  77  includes mating members  83  that engage recesses  85  (see FIG. 86) on the cover  79  to snap fit the base  77  and cover  79  together to form the case  23 . 
     FIG. 8 a  illustrates an inside view of cover  79  of case  23  for microphone assembly  21 . FIG. 7 b  is a cross sectional view of the cover  79  taken along lines A—A of FIG. 8 a . As mentioned above, cover  79  includes recesses  85  that receive the mating members  83  of base  77  during snap assembly of the base  77  and cover  79  into case  23 . Cover  79  further includes a button switch  29 , also as mentioned above. Cover  79  also includes a directional microphone subassembly or module  87  having a microphone element  89  that is electrically connected to the printed circuit board  81 , again as mentioned above. The microphone element may be, for example, one manufactured by Knowles Electronics. 
     The microphone module  87  is generally circular in shape and is mounted on at least one generally circular mounting surface  88  of the cover  79 . Microphone module  87  and surface  88  could be other shapes, however. Microphone module  87  can be removed as a unit from the mounting surface  88  and rotated for various mounting orientations in the cover  79 . The microphone module  87  includes two index tabs  91  that engage any two of index notches  93  located in the cover  79  when the module  87  is placed in a mounted position in cover  79 . The microphone module  87  may, of course, alternatively include only one index tab or more than two index tabs. The index notches  93  are located at, for example, every 30° around the mounting surface  88  of cover  79 . Location of the index notches as such enables proper installation of module  87  into the cover  79  without requiring angle measurements. 
     In an alternative embodiment, the microphone module  87  and mounting surface  88 , instead of having index tabs and notches, respectively, could be identically shaped and adapted to mate together only when the microphone is oriented at certain angles with respect to the cover  79 . More particularly, the module may be, for example, a twelve-sided convex polygon having sides of equal length. The mounting surface or recess would be the same shape and adapted to receive the module in mating relation. In this configuration, each time the module is rotated one position and is mated with the mounting surface, the change in the direction of the microphone orientation is 30° from that of the previous mounted position. A simple counting of sides and rotation of the module, therefore, could easily provide the orientation function of the index tabs and notches discussed above. 
     Microphone module  87  also includes a microphone entry reference port  95 . The reference port  95  is preferably color coded or otherwise identified. Thus, during assembly, depending on the mounting arrangement of the microphone assembly desired, an assembler can quickly and easily set the proper position of the microphone module for desired performance. 
     For example, if a headliner mounting is desired, the manufacturer simply counts one index notch over from the vertical axis of the cover, makes sure the reference port  95  is facing the proper direction, and places the microphone module  87  into the mounting surface  88  of the cover  79 , mating the index tabs  91  into the selected index notches. The microphone module  87  is then locked into place on the mounting surface  88 . The remainder of the case  23  is assembled as discussed above, and then bracket  25  is added. 
     If instead an A-pillar mounting is desired, the assembler similarly counts one notch over from the vertical axis of the cover, makes sure the reference port is facing the proper direction (i.e., 180° from the direction for headliner mounting) and places the microphone module  87  into the mounting surface  88  of the cover  79 , mating the index tabs  91  into the selected index notches. The microphone module  87  is then locked into place on the mounting surface. Again, the remainder of the case  23  is assembled as discussed above, but this time bracket  43  is added. 
     FIGS. 9A,  9   b ,  10   a  and  10   b  illustrate a base inside view, a base cross-sectional view, a cover inside view and a cover cross sectional view, respectively, of microphone assembly  41  for such A-pillar mounting arrangement. As can be seen, these figures are virtually identical to FIGS. 7 a ,  7   b ,  8   a  and  8   b , respectively, for headliner mounting, except that module  87  is rotated 180° (see reference port  95 ), and bracket  43  is used instead of bracket  25 . 
     Thus, the module  87  mounting system of the present invention allows virtually any relationship between acoustical orientation and microphone assembly mounting arrangement while using essentially the same parts. For example, the present invention accommodates right drive cars. Specifically, if headliner mounting for a right drive care were desired, the assembler would simply rotate the microphone module  87  orientation 60° (i.e., two notches) counter-clockwise from its orientation for left drive cars. The same bracket  25  would be used. If A-pillar mounting for a right drive car were instead desired, the assembler would again simply rotate the microphone module  87  orientation 60° (i.e., two notches) counter-clockwise from its orientation for left drive cars. The bracket  43  would then be modified such that it forms a 45° angle to the case in the other direction as that shown in FIG. 3c (i.e., clockwise 90° from its position for left drive cars). 
     Furthermore, the module  87  module system of the present invention allows new and different microphone assembly mounting arrangements (i.e., other than headliner and A-pillar) without changing the design. Moreover, no particular acoustic or microphone expertise or skill is required to manufacture or assemble the product for each mounting arrangement. Further, because the module  87  is lockable by virtue of the mating of the index tabs into the index notches, it is difficult for an installer or consumer to unknowingly modify the microphone orientation within the case and thus adversely affect the microphone performance. 
     In addition, because the microphone module is releasable from the mating surface  88 , an existing microphone assembly can quickly and easily be modified to accommodate a different mounting arrangement. In fact, the microphone module  87  component of the microphone assembly can be removed and used separately from that assembly to accommodate even additional mounting arrangements. For example, the microphone module  87  can be flush mounted as part of a separate surface grill structure in a vehicle. Such surfaces might include the dashboard, the console, etc. The same design, therefore, accommodates different interior styling requirements of different automobile manufacturers. 
     FIGS. 11 a ,  11   b  and  11   c  illustrate the microphone module  87  of the present invention. FIG. 11 a  is a top view of the module  87 . FIG. 11 b  is a side cross sectional view of the module  87  taken along lines A—A in FIG. 11 a . FIG. 11 c  is a bottom view of the module  87 . 
     The module  87  includes a housing  90  and a microphone element  89  mounted therein. The microphone element  89  has a front inlet port  97  and a rear inlet port  99 . An acoustic resistor  101  is located in rear inlet port  99 . Sound is acoustically coupled to the front and rear inlet ports  97  and  99  through windscreen  107  (optional) and sound inlet paths  113  and  115 , respectively. Acoustic plugs  109  and  111  are located in, and form a part of, sound inlet paths  113  and  115 , respectively. To ensure that only sound from acoustic pickup region  117  enters into the front and rear inlet ports  97  and  99 , a sealing material  119  is placed at locations where the housing  90  and the microphone element  89  contact. Acoustic plugs  109  and  111  fit into recesses  121  and  123 , respectively, located in a top surface  124  of housing  90  (with, of course, windscreen  107  removed). Acoustic plugs  109  and  111  sit on surfaces  125  and  127 , respectively, located in the recesses  121  and  123 , and form part of the top surface  124 . 
     Windscreen  107  is then positioned on the top surface  124  and adhered thereto. Adhesive is used on an entire bottom surface  126  of windscreen  107  except that portion  128  generally located over recesses  121  and  123  (see FIG.  12 ). In other words, the bottom surface  126  of windscreen  107  is adhered to the entire top surface  124  of housing  90  except for that portion formed by acoustic plugs  109  and  111 . Some overlap of adhesive over acoustic plugs  109  and  111  may be desirable, however, to prevent sound from entering into sound inlet paths  113  and  115 , respectively, via paths between surfaces of the plugs and surfaces of the recesses. 
     Windscreen  107  is preferably made of a material having low acoustic resistance, such as, for example, cloth, open cell acoustic foam, sintered porous plastics, or screen material. Acoustic plugs  109  and  111  are preferably open cell acoustic foam material. Such material has generally a higher and better controlled acoustical resistance than a cloth material. Both the windscreen and acoustic plugs are preferably water repellant. The windscreen and acoustic plugs operate together to both protect against dirt, dust, liquids, etc. from entering sound inlet paths  113  and  115 , as well as against wind noises. 
     The use of acoustic plugs  109  and  111  provides better wind filtering for the microphone module  87 . However, their use also affects the polar pattern of the microphone module  87  as a whole. Consequently, the acoustic resistance of the acoustic resistor  101 , as well as the effects of the acoustic resistance of the acoustic plugs  109  and  111 , should be considered to achieve an overall desired polar pattern. Acoustic resistor  101  may have a value of 400 ohms, for example, to achieve such a desired polar pattern. 
     As can best be seen in FIG. 11 b , sound inlet paths  113  and  115  are not, unlike the prior art in FIG. 1, cylindrical or a narrow tube as such. Therefore, the sound inlet paths  113  and  115  are substantially nonresonant in the audio frequency range of interest. 
     FIG. 13 is an exploded view of the microphone module  87  of the present invention. As can be seen in FIG. 13, housing  90  of FIG. 11 is comprised of two housing portions,  131  and  133 . Portion  131  has a recess  121  located therein and portion  133  has a recess  123  located therein. Each of portions  131  and  133  includes a mating member  135  and a mating recess  137 , a pocket  139  and an index tab  91 . Alternatively, one portion could include both mating members and the other portion could include both mating recesses. Similarly, of course, one portion could include both index notches. 
     Upon assembly, the housing portions  131  and  133  are brought together with the microphone element located therebetween. The mating members  135  engage mating recesses  137  and the housing portions  131  and  133  are snapped together, at which point surfaces  141  of microphone element  89  contact surfaces in the pockets  139 . As mentioned above, sealing material, such as glue, for example, can be used between surfaces  141  and the surfaces in pockets  139  to form an acoustic seal. Acoustic plugs  109  and  111  are then placed in recesses  121  and  123 , respectively, and windscreen  107  is adhered to top surface  124 , as discussed above. Wires  143  and  145  are then ready to be connected to the printed circuit board  81 , or to such other electrical connection dictated by the desired mounting arrangement. 
     FIGS. 14 a  and  14   b  illustrate an alternate embodiment of the cover and removable module of the directional microphone assembly of the present invention. FIG. 14 a  is a top view, and FIG. 14 b  is a side cross-sectional view, of a cover  147  for a case similar to case  23  described above. Cover  147  has a protruding or bubble portion  149 . As can be seen in FIG. 14 a  and FIG. 15, the protruding portion  149  includes acoustic openings  151 , where sound enters the case, and acoustically opaque portions  153 . Each acoustic opening  151  has a surface  152  adjacent thereto. 
     Cover  147  also includes a removable module or cup  157  mounted in the cover  147 . As described more completely below, the removable module includes a microphone element  89  mounted in a recess  155  of the removable module  157 . As discussed above, the microphone element  89  is electrically connected to the vehicle radio/telephone system via a cable and a printed circuit board. Arrows  163  in FIG. 14 a  show four potential orientations of the removable module  157 , and thus the orientation of the microphone element  89 , in the cover  147 , each orientation being 30° off of reference axis  165 . 
     The removable module  157  also includes front and rear sound inlet paths  159  and  161 , respectively, that acoustically couple the acoustic openings  151  to front and rear inlet ports or tubes  167  and  169  of the microphone element  89 . As explained more completely below, front inlet port  167  also has extension tube  171  acoustically coupled thereto. The sound inlet paths  159  and  161  each have a controlled resonance to achieve a desired directional characteristic. In addition, the combination of recess  155  of the removable module  157  and the open space underneath protruding portion  149  provides an acoustic volume in which a windscreen  163  can be mounted, while still maintaining a desired directional characteristic. 
     FIG. 16 illustrates the windscreen  163 , which may be comprised of two portions—a ring portion  173  and a plug portion  175 . The portions  173  and  175  may both be made of an open cell acoustic foam material, each portion having different porosity. For example, the plug portion  175  may be an open cell reticulated foam material having 30 PPI (pores per inch). The ring portion  173  may be a 2 to 1 compression (felted) open cell foam material having 100 PPI. As is apparent in this example, the plug portion  175  is more porous than the ring portion  173 . 
     Ring portion  173  of windscreen  163  may have an outer diameter “D” of approximately 0.800 to 0.820 inches and an inner diameter “d” of approximately 0.562 inches. Plug portion  175  may likewise have an outer diameter D′ of approximately 0.562 inches. Upon assembly, the plug portion  175  is fitted into the center of the ring portion  173 , and both are placed as a unit between an inner surface of the cover  147  and the removable module  157 . 
     It is also contemplated that ring portion  173  may instead be of toroid shape, and/or may also be placed in the case without the plug portion  173  so that open air exists underneath protruding portion  149  and inside ring/toroid portion  173 . 
     FIG. 17 is a cross-sectional view of the removable module  157  and windscreen  163  mounted in the cover  147 . As can be seen, the plug portion  175  becomes compressed between an inner surface  177  of protruding portion  149  and microphone element  89  and extension tube  171 . Ring portion  173  likewise becomes compressed between inner surface  181  of protruding portion  149  and surface  185  of removable module  157 . Portions of ring portion  173  and plug portion  175  extend into front and rear sound inlet paths  159  and  161 . 
     FIG. 17 also illustrates acoustic openings  151  and adjacent surfaces  152 . As can be seen, surfaces  152  may be sloped at an angle of 0-15° off of horizontal axis  187 . 
     As mentioned above, front inlet port  167  has an extension tube  171  acoustically coupled thereto. Extension tube  171  assists in controlling both the sensitivity and directional characteristic of the microphone assembly. The volume associated with rear inlet port  169  and the volume within the rear portion of the microphone cartridge forms a resonant element. The same holds true for the front volume associated with front inlet port  167  and the volume within the front portion of the microphone element. However, the volumes within the front and rear portions of microphone element  89  may not be the same. Accordingly, extension tube  171  is used to add inertance to the front inlet port or tube  167 . The net effect achieved is two resonant frequencies. In other words, the front and rear volumes are brought closer together by the addition of extension tube  171 . A net result is an extension of the frequency of the desirable polar and directional shape of the frequency response. In addition, the extension tube  171  optimizes the distance between the front and rear entry ports to help achieve design sensitivity goals. 
     The microphone element  89  with extension tube  171  is tuned in conjunction with the volumes of the recess  155  in the removable module  157  and the open air space underneath protruding portion  149  and above removable module  157 . In other words, the performance of microphone element  89  with the extension tube  171  is optimized when it is assembled in the case but non-optimized for application in free space (outside of the case). Optimization, as such, may be achieved by selecting an acoustic resistance for placement in the rear inlet tube  169  that takes into account, again, the volumes of the recess  155  in the removable module  157  and the open air space underneath protruding portion  149  and above removable module  157 . 
     FIG. 18 illustrates the removable module  157  removed from the case  149 . Removable module  157  includes a pocket  189  at the bottom of recess  155  for mounting the microphone element  89 . Removable module  157  also includes a mechanical support  191  for mounting extension tube  171 . A mating surface  193  mates with a corresponding mounting surface  195  (see FIG. 19) within cover  147 . Index tab  197  is engaged with one of index notches  199  (see FIG.  19 ), located at various positions around the mounting surface  195  and within cover  147 . Thus, the removable module, and thus the microphone element  89 , can be mounted and locked at various orientations within the cover, depending on the desired application. As mentioned above, the index notches  199  may be placed, for example, at four locations around the mounting surface  195 , each location being 30° off of reference axis  165 , as shown in FIG. 19. A sealing material may be used between mating surface  193  and mounting surface  195  to prevent acoustic leaking. 
     Many modifications and variations of the present invention are possible in light of the above teachings. Thus, it is to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as described hereinabove.