Abstract:
A microphone assembly generally for hearing aid and communications applications is disclosed. The microphone assembly operates in both directional and non-directional or omni-directional modes. The microphone assembly has front and rear sound inlet tubes, and an actuator switch that may be moved between a first position in which the rear tube is plugged, defining the omni-directional mode, and a second position in which the rear tube is unplugged, defining the directional mode. Circuitry senses the position of the actuator switch and selects a microphone output based on the position sensed.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     Various types of hearing aids are known which have non-directional or omni-directional response characteristics; and, other types of hearing aids are known which have directional response characteristics. Still other prior art hearing aids are known which can be utilized either as directional hearing aids or as omni-directional hearing aids by suitable modification of the structure. However, such other prior art hearing aids, which can be used either as directional or omni-directional devices, have the marked disadvantage that when the aid is used as a omni-directional aid, it will have a given response characteristic relative to frequency, and when the aid is used as a directional aid, it will have an entirely different response characteristic relative to frequency. For example, curve or response line A of  FIG. 3  in prior art U.S. Pat. No. 3,835,263 (Killion) shows a typical response of an omni-directional device wherein the lower frequency portion of the curve is relatively flat and then drops off at the higher frequencies. Curve B in  FIG. 3  of the prior art Killion reference shows the frequency response characteristics of a directional device wherein the frequency response rises from a low value as a relatively straight line to a maximum level and then drops off at the higher frequencies.  
         [0002]     Accordingly, it was an object of the prior art Killion reference to provide a microphone assembly particularly for use with hearing aids, which assembly can be operated either in a directional or a omni-directional mode, but which has essentially the same response characteristics relative to the frequency for sound arriving from the preferred direction whether it is operated in a directional or omni-directional mode.  
         [0003]     The prior art Killion reference, however, did not provide flexibility in independently choosing the resulting frequency response of the microphone in the directional and omni-directional modes. In addition, the prior art Killion reference was acoustically complex and consequently difficult to implement.  
         [0004]     It is therefore an object of the present invention to provide a less acoustically complex assembly having the same frequency response in the omni-directional and directional modes of operation, while also allowing flexibility in adjusting the frequency response of the microphone in the directional mode.  
         [0005]     Other objects of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0006]      FIG. 1  illustrates one embodiment of a microphone assembly according to the present invention  
         [0007]      FIG. 2A  illustrates an exploded view of one embodiment of the microphone assembly of  FIG. 1   
         [0008]      FIG. 2B  illustrates another view of the actuator switch shown in  FIG. 2A .  
         [0009]      FIG. 3  illustrates a cross-sectional assembled view of the microphone assembly of  FIG. 2A .  
         [0010]      FIG. 4  is another assembled cross-sectional view of the microphone assembly of  FIG. 2A .  
         [0011]      FIG. 5  illustrates one embodiment of a microphone equalization circuit of the present invention.  
         [0012]      FIG. 6  illustrates one embodiment of an electronic contact sensor and switch of the present invention.  
     
    
     SUMMARY OF THE INVENTION  
       [0013]     The present invention relates to a microphone assembly for hearing aid and other applications that is capable of operating in a directional mode and a non-directional or omni-directional mode. The microphone assembly has a microphone cartridge and front and rear inlet tubes that couple sound to each side of a diaphragm located in the microphone cartridge. An actuator switch of the assembly may be moved between a position in which the rear inlet tube is plugged, defining the omni-directional mode, and one in which the rear inlet tube is unplugged, defining the directional mode. Thus, a user of a hearing aid, for example, may select whether it is desirable, given the environmental conditions, to operate in the directional mode or the omni-directional mode.  
         [0014]     Depending on the mode selected by the user, circuitry of the assembly selects a given output from the microphone. More specifically, the circuitry, which may be wholly or partially integrated into the microphone cartridge or an assembly housing, senses the position of the actuator switch, i.e., whether the rear inlet tube is plugged or unplugged, and selects an output that is desirable based on the operative mode. For example, if the rear inlet tube is unplugged, indicating the directional mode, the circuitry may select an equalized output from the microphone, or one with lower gain, or one including greater environmental noise reduction, for example. If, on the other hand, the rear inlet tube is plugged, indicating the omni-directional mode, the circuitry may select a non-equalized output from the microphone, or one with higher gain, or one including less environmental noise reduction, for example. In any case, the circuitry senses the mode selected and dictates the output from the microphone correspondingly.  
         [0015]     Other aspects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0016]      FIG. 1  illustrates one embodiment of a microphone assembly according to the present invention. Microphone assembly  1  comprises a microphone housing  3  that encloses a microphone cartridge  5  therein. Microphone cartridge  5  has a diaphragm  6 , a front sound inlet port or opening  7  and a rear sound inlet port or opening  9 . Front sound inlet port  7  and rear sound inlet port  9  engage front sound inlet tube  11  and rear sound inlet tube  13 , respectively, of microphone housing  3 . An acoustic resistor  15  is located in rear sound inlet port  9 . Acoustic resistor  15 , however, may instead be located in rear sound inlet tube  13 .  
         [0017]     Microphone assembly  1  further comprises an actuator switch  10  that modifies the directional characteristics of the microphone assembly  1 . Specifically, when the actuator switch  10  is in a directional position represented by the dotted lines in  FIG. 1 , the rear sound inlet tube  13  is uncovered and the microphone assembly  1  acts as a directional microphone. When the actuator switch  10  is moved to an omni-directional position represented by the solid lines in  FIG. 1 , the rear sound inlet tube  13  is plugged and the microphone assembly  1  acts as a non-directional or omni-directional microphone. We have found that an exact acoustic plug or seal of sound inlet tube  13  is not required, and that a 30-40K CGS acoustical ohm plug or seal is sufficient to achieve a desired omni-directional performance.  
         [0018]     In addition, actuator switch  10  has an electrical contact  12  that, when actuator switch  10  is in omni-directional position, makes electrical contact between conductors  14  and  16 . Electrical contact between the conductors  14  and  16  as such serves to indicate that the omni-directional position has been selected. Alternatively, the microphone assembly  1  may be configured such that electrical contact between the conductors  14  and  16  serves to indicate that the directional position has been selected.  
         [0019]     Microphone cartridge  5  has electrical outputs  17  and  19  that represent the non-equalized outputs of the microphone cartridge  5 . Electrical outputs  17  and  19  are electrically connected to a microphone equalization circuit  21 . The microphone equalization circuit  21  provides an adjustable low frequency amplification for the outputs  17  and  19  of microphone cartridge  5 . Microphone equalization circuit  21  has electrical outputs  23  and  25  that, along with electrical output  17  of the microphone cartridge  5 , electrically connect to an electronic contact sensor and switch  27 . Electronic contact sensor and switch  27 , depending on the position of actuator switch  10 , selects either output  17  of the microphone cartridge  5  or output  23  of microphone equalization circuit  21 . Specifically, when the actuator switch  10  is in the directional position, no contact is made between conductors  14  and  16 , and electronic contact sensor and switch  27  selects the output  23  from the microphone equalization circuit  21 . As mentioned above, the microphone equalization circuit  21  increases the low frequency output of the microphone cartridge, which is desirable to obtain a more frequency balanced sound pick-up.  
         [0020]     When the actuator switch  10  is in the omni-directional position, contact is made between conductors  14  and  16 . Electronic contact sensor and switch  27  senses the contact between conductors  14  and  16  and consequently selects output  17  of microphone cartridge  5 . In the omni-directional position as such, no equalization by microphone equalization circuit  21  is desirable due to the inherently flat frequency response of the microphone cartridge  5  when the rear sound inlet tube is sufficiently plugged.  
         [0021]     In either the directional or non-directional mode, electronic contact sensor and switch  27  provides microphone outputs  29  and  31  to an input circuit, such as, for example, a hearing aid amplifier.  
         [0022]     It should be understood that the electronic contact sensor and switch  27  and microphone equalization circuit  21  may be partially or wholly integral to the microphone housing  3  or microphone cartridge  5 . In addition, the functionality of the electronic contact sensor and switch  27  and microphone equalization circuit  21  may be combined in a single circuit, such as a hybrid circuit, for example, having electrical outputs  17  and  19  and conductors  14  and  16 , as well as microphone outputs  29  and  31 , electrically connected thereto. Such a single circuit (not shown) may similarly be partially or wholly integral to the microphone housing  3  or microphone cartridge  5 .  
         [0023]     In another embodiment, the functionality of the electronic contact sensor and switch  27  and microphone equalization circuit  21  may be performed by hearing aid circuitry, such as, for example, hearing aid amplifier circuitry. Again, such circuitry may be partially or wholly integral to the microphone housing  3  or microphone cartridge  5 .  
         [0024]     While the embodiment of  FIG. 1  shows the electronic contact and sensor switch  27  selecting an equalized or non-equalized output based on the mode (i.e., directional or non-directional) selected by the actuator switch  10 , other types of outputs are contemplated and within the scope of the present invention. For example, the electronic contact and sensor switch  27  may alternatively (or additionally) adjust the gain based on the mode selected. More specifically, if the actuator switch  10  is in the directional position, such that both front and rear sound inlet tubes  11  and  13  are open and no contact is made between conductors  14  and  16  as discussed above, the electronic contact and sensor switch  27  may select a microphone output with a higher gain, for example. If, on the other hand, the actuator switch  10  is in the omni-directional position, such that the rear sound inlet is plugged and contact is made between conductors  14  and  16  as discussed above, the electronic contact and sensor switch  27  may select a microphone output having a lower gain or no gain, for example. In such a configuration, the microphone equalization circuit  21  may be replaced with gain circuitry (not shown), for example, or the electronic contact and sensor switch  27  may include its own circuitry for controlling gain, or completely separate gain circuit may be included.  
         [0025]     As another example, the electronic contact and sensor switch  27  may alternatively (or additionally) electronically control or select environmental noise reduction based on the mode selected. More specifically, if the actuator switch  10  is in the directional position as discussed above, the electronic contact and sensor switch  27  may select more environmental noise reduction, for example. If, on the other hand, the actuator switch  10  is in the omni-directional position as discussed above, the electronic contact sensor and switch  27  may select less environmental noise reduction, for example. In such a configuration, the microphone equalization circuit  21  may be replaced with electronic noise reduction circuitry (not shown), for example, or the electronic contact and sensor switch  27  may include its own electronic noise reduction circuitry, or completely separate electronic noise reduction circuitry may be included.  
         [0026]     Environmental noise reduction as such may comprise any type of electronic signal processing that reduces the amount of environmental noise heard by a user of a hearing aid.  
         [0027]     In any case, the electronic and sensor switch  27  selects a microphone output (or in other words, an input to hearing aid or other circuitry) based on the mode selected by actuator switch  10 . Again, regardless of the configuration or functionality of the circuitry used, such circuitry may be partially or wholly integrated into the microphone housing  3  or microphone cartridge  5 .  
         [0028]      FIG. 2A  illustrates an exploded view of one embodiment of the microphone assembly of  FIG. 1  built in accordance with the present invention. Microphone assembly  33  comprises a microphone housing  35  having a front housing portion  37  and a rear housing portion  39 . Microphone assembly  33  further comprises a microphone cartridge  41  that has a front sound inlet port  43  and a rear sound inlet port  45 . Upon assembly, front sound inlet port  43  of the microphone cartridge  41  engages the front sound inlet tube  47  of the front housing portion  37 , and rear sound inlet port  45  of the microphone cartridge  41  engages the rear sound inlet tube  49  of the rear housing portion  39 . An acoustic resistor  51  is shown in  FIG. 2A  as being located in the rear sound inlet port  45  of the microphone cartridge  41 . Front housing portion  37  has a tab  53  that, upon assembly, releasably engages a recess  55  located in the rear housing portion  39 . Rear housing portion  39  likewise has a tab (now shown) that releasably engages a recess  57  located in the front housing portion  37 . Such snap-fit assembly configuration acts to enclose the microphone cartridge  41  in the microphone housing  35 , and releasably lock the front housing portion  37  and rear housing portion  39  together.  
         [0029]     Microphone cartridge  41  is electrically connected to a circuit board  59  that includes a microphone equalization circuit  61  and an electronic contact sensor and switch  63  mounted on the circuit board  59 . Electrical connections  65  (V+, output, ground) electrically connect the microphone cartridge  41  to the circuit board  59 . Circuit board  59 , and specifically electronic contact sensor and switch  63 , is connected to conductors  67  and  69 , similarly as discussed above with respect to conductors  14  and  16  of  FIG. 1 . Conductors  67  and  69  are mechanically mounted in grooves  71  and  73 , respectively, located in the front housing portion  37 .  
         [0030]     Circuit board  59  is mounted to a bottom portion of the microphone housing  35 . Specifically, front housing portion  37  includes a ledge  109  that receives an end of an undersurface of circuit board  59 . Rear housing portion  39  includes releasable tabs  111  that receive an opposite end of the undersurface of circuit board  59 . Circuit board  59 , therefore, snap fits to the microphone housing  35 . Circuit board  59  also includes microphone outputs  66  to an input circuit, such as, for example, a hearing aid amplifier.  
         [0031]     Microphone assembly  33  further comprises an actuator switch  75  that is mounted on the microphone housing  35 . Two different views of actuator switch  75  are shown in  FIGS. 2A and 2B . The actuator switch  75  has a front sound inlet protective screen  77  and a rear sound inlet protective screen  79  for acoustical coupling with the front sound inlet tube  47  and rear sound inlet tube  49 , respectively, of the microphone housing  35 . Actuator switch  75  further includes a raised portion  76  for sliding the actuator switch  75 , and a member  81  mounted on an underside of the actuator switch  75 . The member  81  has a portion  83  for plugging the rear sound inlet tube  49 , and a conductive portion  85  for contacting surfaces  87  and  89  of conductors  67  and  69 , respectively. An underside of actuator switch  75  includes a post  91  that engages a notch  93  of member  81 , and a stop  94  that abuts an end of the member  81  having the notch  93 . Such configuration aligns the member  81  in the proper position so that it can travel in, and be guided by, a channel  95  located in both front housing portion  37  and rear housing portion  39 . Additionally, stop  94  prevents excessive motion in either direction of the member  81  within the channel  95 .  
         [0032]     As mentioned above, the actuator switch  75  is mounted on the microphone housing  35 . Actuator switch  75  includes tabs  97  and  99  that, upon assembly, are pressed together and fit into channel  95 . A surface  101  of tab  99  and a surface  103  of tab  97  engage surfaces  105  and  107 , respectively, in the channel  95  of microphone housing  35 .  
         [0033]      FIG. 3  illustrates a cross-sectional assembled view of the microphone assembly  33  of  FIG. 2A . As can be seen, when the actuator switch  75  is in a directional position as indicated by the solid lines, plugging portion  83  of member  81  resides in a retaining pocket  113  located in the rear housing portion  39  of microphone housing  35 . Also, in the directional position, conductive portion  85  of member  81  electrically contacts surfaces  87  and  89  of conductors  67  and  69 , respectively, indicating that the directional position has been selected. To switch to the omni-directional position, a user pushes against raised member  76  of actuator  75  in a direction indicated by dotted arrow  115  until actuator switch  75  is in a omni-directional position as indicated by the dotted lines. As the actuator switch is moved, plugging portion  83  rides up incline  117  of retaining pocket  113  until it seats in the rear sound inlet tube  49 . Conductive portion  85  of member  81  is likewise moved in the direction of dotted arrow  115  causing electrical contact between surfaces  87  and  89  of conductors  67  and  69  to be interrupted, indicating that the omni-directional position has been selected.  
         [0034]      FIG. 4  is another assembled cross-sectional view of the microphone assembly  33  of  FIG. 2A . The view of  FIG. 4  illustrates the electrical connection of conductors  67  and  69  to circuit board  59 , as well as surfaces  87  and  89  that are electrically connected together via conductive portion  85  of member  81  (as shown in  FIGS. 2A and 3 ).  
         [0035]      FIG. 5  illustrates one embodiment of the microphone equalization circuit of the present invention. Inputs  17  and  19  and outputs  23  and  25  of circuit  119  in  FIG. 5  correspond to the inputs and outputs of the microphone equalization circuit  21  of  FIG. 1 . Circuit  119  may be an integrated circuit portion coupled to an external capacitor  121  that sets the shape of the low frequency equalization characteristic. Circuit  119  also includes a electronic zener trimmer portion that enables electronic adjustment of the amplification provided by the circuit.  
         [0036]      FIG. 6  illustrates one embodiment of the electronic contact sensor and switch of the present invention. Circuit  125  includes inputs  127  and  129  that are electrically connected to the conductors, such as conductors  14  and  16  of  FIG. 1 . Outputs  131  and  133  are electrically connected to an input circuit, such as, for example, a hearing aid amplifier, as discussed above. Outputs  131  and  133  of  FIG. 6  correspond to outputs  29  and  31 , respectively, of the electronic contact sensor and switch  27  of  FIG. 1 .  
         [0037]     Circuit  125  further includes inputs  135  and  137  that correspond to inputs  23  and  17 , respectively, of  FIG. 1 . For the embodiment of  FIG. 1 , when inputs  127  and  129  are electrically connected (i.e., conductors  14  and  16  are electrically connected together in the omni-directional mode), output  133  of circuit  125  is electrically connected to input  137  such that the output signal at output  133  is not equalized by circuit  119  of  FIG. 5 . When inputs  127  and  129  are not electrically connected (i.e., conductors  14  and  16  are not electrically connected in the directional mode), output  133  of circuit  125  is electrically connected to input  135  such that the output signal at output  133  is equalized by circuit  119  of  FIG. 5 . If, alternatively as discussed above, it is desired to have electrical coupling of conductors  14  and  16  produce the opposite switching results, the input signals connected to inputs  135  and  137  of circuit  125  of  FIG. 6  would be reversed.  
         [0038]     Circuit  125  of  FIG. 6  may, for example, utilize n and p channel CMOS integrated circuit technology.  
         [0039]     In view of the above-detailed description of the present invention and associated drawings, other modifications and variations will now become apparent to those skilled in the art. It should also be apparent that such other modifications and variations may be effected without departing from the spirit and scope of the present invention.