Abstract:
Apparatus for use as an in-the-ear hearing aid. The apparatus includes a housing having a shell and a face plate, wherein the shell is molded to custom fit a hearing aid wearer&#39;s ear. A first non-directional microphone system is included having a first output signal representative of the sound received. A second non-directional microphone system is included having a second output signal representative of the sound received. A switch mechanism is included having an operator extending through the housing for switching the in-the-ear hearing aid between a non-directional mode and a directional mode. In the directional mode, the microphone system is adjustable to account for component tolerances. The switched directional/non directional microphone feature is employed in a custom in-the-ear Contralateral Routing of Signals (CROS) or Bilateral Routing of Signals (BiCROS) two instrument hearing aid system.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a continuation-in-part of co-pending application Ser. No. 08/763,520 filed on Dec. 11, 1996. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    The present invention relates to a microphone system which may be used with an in-the-ear hearing aid system. In particular, the present invention relates to an adjustable microphone system, which may be used with an in-the-ear hearing aid, which allows the wearer to switch between a non-directional (or omni-direction) mode or a directional mode.  
           [0003]    Typical hearing aids either include a non-directional or directional hearing aid system. A non-directional hearing aid system allows the wearer to pickup sounds from any direction. When a hearing aid wearer is trying to carry on a conversation within a crowded room, a non-directional hearing aid system does not allow the wearer to easily differentiate between the voice of the person the wearer is talking to and background or crowd noise. A directional hearing aid helps the wearer to hear the voice of the person he or she is having a conversation with, while reducing the miscellaneous crowd noise present within the room.  
           [0004]    Traditionally, directional hearing aids are implemented with a single microphone having inlets to cavities located in front and back of a diaphragm. Directionality with a single microphone is accomplished with an acoustic resistor placed across a hole in the back inlet of the microphone acting in combination with the compliance formed by the volume of air behind the diaphragm. This system is termed a first order pressure gradient directional microphone because the microphone output is a function of the pressure differential across the diaphragm.  
           [0005]    One measure of the amount of directivity of a directional hearing aid system is a polar directivity pattern  10  as shown in FIG. 1. The polar directivity pattern  10  shows the amount of pickup at a specific frequency (in terms of attenuation in dB) of a directional hearing aid system as a function of azimuth angle of sound incidence. Accurate measurement of a polar directivity pattern requires an anechoic chamber. An anechoic chamber is an enclosed room that has minimum reflection of sound from its inner wall surfaces and that attenuates ambient sounds entering from the outside. Thus, inside an anechoic chamber, the direction of arrival of sound can be controlled so that it comes from only one specific angle of incidence.  
           [0006]    A cardioid or heart-shaped polar pattern produces a directivity index of about 3-4 dB. The directivity index is the ratio of energy arriving from in front of the hearing aid wearer to the random energy incident from all directions around and imaginary sphere with the hearing aid at its center. However, a super cardioid polar pattern  14 , as shown in FIG. 2, which can also be obtained with a first order pressure gradient directional hearing aid microphone, produces a 5-6 dB directivity index. It has been found that producing a super-cardioid polar pattern  14  requires 1.72 times greater front-to-rear microphone port spacing than a cardioid polar pattern  12 . Because of limited space, a super cardioid directivity pattern is more difficult to achieve using a single directional microphone in a full-concha custom in-the-ear hearing device.  
           [0007]    Conventional behind-the-ear type hearing aids have included a main body and a hook extending from the main body and arrange to engage the upper end of the ear lobe of the wearer to hang the main body on the ear. Known versions of behind-the-hearing aids that had variable amounts of directionality use mechanical shutters or valves to adjust the amount of directionality. For example, see U.S. Pat. No. 3,798,390 to Gage et al.; U.S. Pat. No. 3,836,732 to Johanson et al.; and U.S. Pat. No. 4,051,330 to Cole. Other known behind-the-ear hearing aid systems, such as U.S. Pat. No. 5,214,709 to Ribic suggests a behind-the-ear hearing aid system which includes the use of more than one non-directional microphone to make a directional microphone behind-the-ear hearing aid system.  
           [0008]    Persons with an unaidable unilateral hearing loss or persons having one ear that cannot be aided with a hearing aid (known as a dead ear) and one ear with some aidable hearing loss often have great difficulty communicating in high noise levels. In such hearing loss configurations, this difficulty occurs because of the loss of the auditory system&#39;s normal ability to suppress noise, which is the expected result of the cross-correlation capability of the brain using the balanced, fused, binaurally-processed inputs from the two normal cochleas of a normal hearing person.  
           [0009]    Contralateral Routing Of Signals (CROS) and Bilateral Routing of Signals (BiCROS) hearing aids, respectively, are often employed for such persons since&#39;they often have great difficulty wearing only one hearing aid. In essence, two instrument CROS and BiCROS systems take sound from the bad ear, process it, then send the processed sound via hard wire, RF, or induction transmission to a receiver in the other ear.  
           [0010]    CROS systems are utilized for individuals with one unaidable ear and one ear with normal hearing or a mild hearing loss. A microphone is worn on the unaidable ear, and the receiver is worn on the better ear. BiCROS systems are utilized for individuals having one unaidable ear and one ear needing amplification. In the BiCROS system, a microphone is worn on each ear, and the receiver is worn on the better ear. CROS and BiCROS hearing aids overcome the loss of about 6 dB caused by the head blocking and diffracting sounds incident to one ear (the dead side) as they cross over to the better ear.  
           [0011]    It is desirable to have an in-the-ear hearing aid system which allows the wearer to switch between a non-directional (omni-directional) and a directional hearing aid mode. Further, it is desirable to have an in-the-ear hearing aid system having an adjustable directional microphone system, wherein the adjustable directional microphone system. Further, it is desirable to have an in-the-ear hearing aid microphone system having an adjustable directional microphone system to allow compensation for small ears where the microphone inlets cannot be spaced far apart. It is also desirable to have an in-the-ear hearing aid microphone system which allows the in-the-ear hearing aid microphone system to be adjusted for manufacturing tolerances between the individual microphones. Finally, it is desirable to have a CROS or BiCROS hearing aid which offers a switched directional/non-directional capability.  
         SUMMARY OF THE INVENTION  
         [0012]    The present invention includes an apparatus for use as an in-the-ear hearing aid. The apparatus includes a housing having a shell and a face plate, wherein the shell is molded to custom fit a hearing aid wearer&#39;s ear. A first non-directional microphone system is included having a first inlet opening in the face plate for receiving sound, and having a first output signal representative of the sound received. A second non-directional microphone system is included having a second inlet opening in the face plate for receiving sound and having a second output signal representative of the sound received. A switch mechanism is provided having an operator extending through the housing for switching the in-the-ear hearing aid between a non-directional mode and a directional mode.  
           [0013]    The switch has an open position and a closed position. When the switch is in the closed position, the in-the-ear hearing aid operates in a directional mode. When the switch is in an open position, the in-the-ear hearing aid operates in a non-directional mode.  
           [0014]    The apparatus may further include means for summing, selectively coupled to the first non-directional microphone system and the second non-directional microphone system, having a summed output signal representative of the sum of the first output signal and the second output signal. When the hearing aid is in the directional mode, the output signal has a polar directivity pattern representative of the summed output signal, the means for summing may further comprise means for adjusting the polar directivity pattern of the summed output signal. The means for adjusting the polar directivity pattern may include an inverting amplifier coupled to the second microphone system, and an adjustable low pass filter coupled to the inverting amplifier. In one embodiment, the adjustable phase delay includes an adjustable phase delay having an adjustable capacitor. The means for adjusting the polar directivity may further include an adjustable amplifier coupled to the second microphone system.  
           [0015]    In one embodiment, the first inlet opening and the second inlet opening are relatively close together. In one particular embodiment, the first inlet opening and second inlet opening are less than one/half inch apart, and the first inlet opening and the second inlet opening are located in approximately the same plane, which is generally horizontal to the ground when the in-the-ear hearing aid is located in a wearer&#39;s ear.  
           [0016]    In another embodiment, the present invention includes a microphone system for use with an in-the-ear hearing aid. The system includes a first non-directional microphone system having a first inlet opening for receiving sound and having a first output signal representative of the sound received. A second non-directional microphone system is included having a second inlet opening for receiving sound having a second output signal representative of the sound received. Means are provided for coupling the first non-directional microphone system to the second non-directional microphone system for switching the in-the-ear hearing aid between a non-directional mode and a directional mode.  
           [0017]    The means for coupling may be a switch having a closed position and an open position, and wherein when the switch is in the open position, the in-the-ear hearing aid is in the non-directional mode, and when the switch is in a closed position, the in-the-ear hearing aid is in a directional mode.  
           [0018]    The second non-directional microphone system may further include means for inverting the second output signal. The second non-directional microphone system may further include means for adjusting the phase delay of the second output signal relative to the first output signal. The means for adjusting the phase delay may include a low pass filter having an adjustable capacitor. Further, the second non-directional microphone system may further include means for adjusting the amplitude of the second output signal relative to the first output signal.  
           [0019]    The present invention may include means for summing the first output signal and the second output signal. The means for summing may have an output coupled to an amplifier. The amplifier may include a phase delay.  
           [0020]    In yet another embodiment, the present invention may integrate two switched directional/non-directional microphone systems as described above into a two instrument, in-the-ear CROS or BiCROS hearing aid. The connection between the two instruments of the CROS or BiCROS hearing aid may be made via a hard wire connection, RF, or induction transmission. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]    Other objects of the present invention and many of the attendant advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, in which like reference numerals designate like parts throughout the figures thereof, and wherein:  
         [0022]    [0022]FIG. 1 is a cardioid polar directivity pattern of an in-the-ear hearing aid;  
         [0023]    [0023]FIG. 2 is a super cardioid polar directivity pattern of an in-the-ear hearing aid;  
         [0024]    [0024]FIG. 3 is a perspective view of an in-the-ear hearing aid in accordance with the present invention;  
         [0025]    [0025]FIG. 4 is a system block diagram of one embodiment of the hearing aid in accordance with the present invention;  
         [0026]    [0026]FIG. 5 is a schematic circuit diagram of one embodiment of the in-the-ear hearing aid in accordance with the present invention;  
         [0027]    [0027]FIG. 6 is a pictorial drawing of a two instrument BiCROS hearing aid with a wire connecting the two units;  
         [0028]    [0028]FIG. 7 is a graphical embodiment of the polar directivity pattern of a two instrument BiCROS hearing aid with both instruments switched into directional mode;  
         [0029]    [0029]FIG. 8 is a system block diagram of an embodiment of a BiCROS in-the ear hearing aid having a switched directional/non-directional capability; and  
         [0030]    [0030]FIG. 9 is a schematic circuit diagram of an embodiment of a two instrument BiCROS hearing aid having switched directional/non-directional capabilities. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0031]    In FIG. 3, an in-the-ear hearing aid is generally shown at  16 . The in-the-ear (ITE) hearing aid  16  includes a housing  18  having a face plate  22  and a molded shell  20 . The molded shell  20  is adhered to the face plate  22 , indicated along line  24 . The molded shell  20  is custom molded to fit each individual hearing aid wearer by known processes, such as making an impression of the individual hearing aid wearer&#39;s ear and forming the molded shell based on that impression. The face plate  22  is coupled to a circuit board (not shown) located inside the ITE hearing aid  16 , which contains the circuitry for the hearing aid device.  
         [0032]    Extending through the in-the-ear hearing aid  16  and specifically face plate  22 , is a battery door  26 , a volume control  28 , a switch S 1 , a microphone mic F, and a microphone mic B. The battery door  26  allows the hearing aid wearer access to the in-the-ear hearing aid  16  for changing the battery (not shown). The volume control  28  allows the hearing aid wearer to adjust the volume or amplification level of the hearing aid  16 .  
         [0033]    Switch S 1  extends through the housing  18  and specifically face plate  22 . Switch S 1  allows the hearing aid wearer to manually switch the in-the-ear hearing aid  16  between a non-directional or directional hearing aid mode. Switch S 1  is electronically coupled to the circuit contained within the in-the-ear hearing aid  16 , which will be described in further detail later in the specification. With the novel idea of switch S 1 , a hearing aid wearer can switch to a non-directional hearing aid mode to hear sounds from all directions, or a directional hearing aid mode, such as for reducing background noise when carrying on a conversation in a crowded room.  
         [0034]    Microphone mic F and microphone mic B include inlet tubes  30 ,  32  which protrude through the in-the-ear hearing aid face plate  22 . Microphone mic F and microphone mic B are spaced a relatively short distance apart, preferably less than ½ inch. In one preferred embodiment, microphone mic F and microphone mic B are preferably ⅓ of an inch apart.  
         [0035]    The axis of directionality is defined by a line drawn through the inlet tube  30  and inlet tube  32  in face plate  22 , indicated at  34 . The in-the-ear hearing aid  16  in accordance with the present invention is of a molded design such that the axis of directionality  34  is relatively horizontal to the floor when the in-the-ear hearing aid  16  is positioned within the hearing aid  16  wearer&#39;s ear. With this design, optimum directional performance of the in-the-ear hearing aid  16  is achieved.  
         [0036]    Referring to FIG. 4, a block diagram showing the directional microphone system in accordance with the present invention, for use with an in-the-ear hearing aid is generally shown at  36 . The directional microphone system  36  utilizes two non-directional microphone circuits to achieve a directional microphone signal. The directional microphone system  36  includes a first non-directional microphone system  38  and a second non-directional microphone system  40 . The output signals from the second non-directional microphone system  40  (indicated by signal  44 ) may be electrically coupled through switch S 1 , and summed at node  46  with the first non-directional microphone system  38  (indicated by signal  42 ) The resulting output signal is indicated at  48 . The output signal  48  is electrically coupled to a hearing aid circuit  50 . For example, the hearing aid circuit  50  may be a linear circuit, a compression circuit, an adaptive high-pass filter, and may include a high-power output stage.  
         [0037]    The in-the-ear hearing aid  16  may be switched between a non-directional mode and a directional mode through the operation of switch S 1 . In the non-directional mode switch S 1  is open (as shown), and non-directional microphone mic F feeds directly into hearing aid circuit  50 . For operation in a directional mode, switch S 1  is closed, and the first non-directional microphone system  38  and second non-directional microphone system  40  output signals  42  and  44  are summed at summing node  46 , with the resulting output signal  48  being coupled to hearing aid circuit  50 .  
         [0038]    In one embodiment, the second non-directional microphone system  40  includes non-directional microphone mic B, an inverter  52 , an adjustable pulse delay  54 , and an adjustable gain  56 . The output signal of microphone mic B is coupled to inverter  52 , indicated at  58 . The output signal of inverter  52  is coupled to the adjustable pulse delay  54 , indicated at  60 . The output of adjustable phase delay  54  is coupled to the adjustable gain  56 , indicated at  62 . The output of the adjustable gain  56  is coupled to switch S 1 , indicated at  64 .  
         [0039]    The output signal  58  of microphone mic B is inverted by inverter  52 . Further, when switch S 1  is closed, the phase delay  54  of the output of mic B may be adjusted relative to the output of microphone mic F. Similarly, adjustable gain  56  adjusts the amplitude of the output signal received from mic B relative to the output signal  42  from microphone mic F. By providing such adjustment, the hearing aid manufacturer and/or the hearing aid dispenser may vary the polar directivity pattern of the in-the-ear hearing aid. The adjustable non-directional microphone system  40  allows the polar pattern to be adjusted to compensate for small ears which do not allow larger inlet spacing. Further, the adjustable non-directional microphone system  40  allows for adjustments to compensate for the differences in manufacturing tolerances between non-directional microphone mic F and non-directional microphone mic B.  
         [0040]    The output signal  48  from first non-directional microphone system  38  and second non-directional microphone system  40  may be amplified by passing it through an amplifier  66 . The resulting output signal of amplifier  66 , indicated at  68 , is coupled to the hearing aid circuit  50 .  
         [0041]    Referring to FIG. 5, a schematic diagram of one preferred embodiment of the-in-ear hearing aid directional microphone system  36  is shown. Non-directional microphone mic F has a coupling capacitor C 1  coupled to its output. Resistor R 1  is electrically coupled between coupling capacitor C 1  and summing node  46 . Non-directional microphone mic B has a coupling capacitor C 2  coupled to its output. Coupled to the output of C 2  is inverter  52  with adjustable phase delay  54 . The adjustable phase delay is an adjustable low pass filter. The inverter  52  is an operational amplifier OPAMP  1 , shown in an inverting configuration. Coupled between capacitor C 2  and the input node  70  of OPAMP  1  is resistor R 2 . Coupled between OPAMP  1  input node  70  and an OPAMP  1  output node  72  is resistor R 3 . Similarly, coupled between OPAMP  1  input node  70  and OPAMP  1  output node  72  is a capacitor C 3 .  
         [0042]    As previously described herein, OPAMP  1  inverts the output signal received from non-directional microphone mic B. As such, when the output signal  42  and output signal  44  are summed at summing node  46 , the signals are subtracted, resulting in output signal  48 .  
         [0043]    The gain between the input of OPAMP  1  and the output of OPAMP  1  is indicated by the relationship R 3 /R 2 . In one preferred embodiment, R 3  equals R 2 , resulting in a unity gain output signal from OPAMP  1 .  
         [0044]    The phase delay  54  low pass capacitor C 3  may be adjustable. By adjusting capacitor C 3 , and/or resistor R 3 , the phase delay of the non-directional microphone mic B output relative to the non-directional microphone mic F may be adjusted. Coupled to the output node  72  of OPAMP  1  is a resistor R 5  in series with an adjustable resistor or potentiometer R 6 . Further, coupled to output signal  48  is an inverting operational amplifier, OPAMP  2  having an input node  74  and an output node  76 . Coupled between the input node  74  and the output node  76  is resistor R 4 . Also coupled between the input node 74 and the output node  76  is a capacitor C 4 . It is recognized that capacitor C 4  and resistor R 3  and R 4  may also be adjustable.  
         [0045]    When switch S 1  is open, the resulting amplification or gain from the output from non-directional microphone mic F is the ratio of resistors R 4 /R 1 . When switch S 1  is closed, the output gain contribution from mic B is determined by the ratio of R 4 /(R 5  plus R 6 ). By adjusting the adjustable potentiometer R 6 , the amplitude of non-directional microphone mic B of the output signal relative to the output signal amplitude of non-directional microphone mic F may be adjusted. As previously stated herein, by adjusting both capacitor C 3  and resistor R 6 , the hearing aid may be adjusted to vary the polar directivity pattern of the in-the-ear hearing aid from cardioid (FIG. 1) to super cardioid (FIG. 2), as desired.  
         [0046]    In one preferred embodiment, the values for the circuit components shown in FIG. 5 are as follows:  
                       TABLE 1                                       C1 = .01 uF           C2 = .01 uF           C3 = .0022 uF           C4 = 110 pF           R1 = 10 K           R2 = 10 K           R3 = 10 K           R4 = 1 M           R5 = 10 K           R6 = 2.2 K                      
 
         [0047]    Non-directional microphone mic F and non-directional microphone mic B can be non-directional microphones as produced by Knowles No. EM5346. Operational amplifiers OPAMP  1  and OPAMP  2  may be inverting Gennum Hearing Aid Amplifiers No. ¼ LX509.  
         [0048]    The hearing aid in accordance with the present invention allows a person wearing an in-the-ear hearing aid to switch between a non-directional mode and a directional mode by simple operation of switch S 1  located on the in-the-ear hearing aid  16 . The circuit components which makeup the directional microphone system  36  and the hearing aid circuit  50  are all located within the hearing aid housing  18  and coupled to the inside of face plate  22 . Further, by adjustment of the adjustable phase delay  54  and adjustable gain  56 , the directional microphone system  36  may be adjusted to vary the polar directivity pattern to account for manufacturing differences. It may be desirable to adjust the polar directivity pattern between cardioid and super cardioid for various reasons, such as to compensate for limited inlet spacing due to small ears or to compensate for the manufacturing tolerances between non-directional microphone mic F and non-directional microphone mic B. It is also recognized that capacitor C 4  and resistor R 4  may be adjustable to compensate for each individual&#39;s hearing loss situation.  
         [0049]    With the novel design of the present invention, the associated circuitry of the present invention allows the two non-directional microphones mic B and mic F to be positioned very close together and still produce a directional microphone system having a super cardioid polar directivity pattern. Further, the directional microphone system in accordance with the present invention is able to space the two microphones less than one inch apart, and in a preferred embodiment, ⅓ of an inch apart in order for the directional microphone system in accordance with the present invention to be incorporated into an in-the-ear hearing aid device. The in-the-ear hearing aid  16  circuitry, including the directional microphone system  36  circuitry and the hearing aid circuit  50  circuitry, utilize microcomponents and may further utilize printed circuit board technology to allow the directional microphone system  36  and hearing aid circuit  50  to be located within a single in-the-ear hearing aid  16 .  
         [0050]    In FIG. 6, a BiCROS, in-the-ear (ITE) hearing aid system is generally shown at  101 . CROS and BiCROS systems are designed for individuals with little or no hearing in one ear and some hearing capability in the other ear. CROS/BiCROS systems take sound from the bad ear and send it, via hard wire (illustrated), RF (not illustrated), or induction transmission (not illustrated, but as in the Telex Wireless CROS system) to a receiver in the other ear. The BiCROS, ITE hearing aid  101  of FIG. 6 includes two separate instruments  16 A and  16 B (each to be placed in an ear of the individual) and a wire cord  102  interconnecting the two instruments  16 A and  16 B at wire cord junctions  124 A and  124 B. One of the instruments  16 A will function as a transmitter unit and will be placed in the unaidable ear of the individual. The other instrument  16 B will function as a receiver and will be placed in the better ear of the individual. However, since both instruments  16 A and  16 B have the dual microphone system, each instrument  16 A and  16 B can be designated as either a transmitter or a receiver in the device configuration.  
         [0051]    An in-the-ear CROS system (not-illustrated) will operate in a manner similar to the illustrated BiCROS system shown in FIG. 6, except that CROS systems are generally utilized for individuals with one unaidable ear and one ear with a normal hearing or a mild hearing loss. Thus, in a CROS system, a microphone set is worn only in the unaidable ear, and the receiver is worn in/on the better ear, while in the illustrated BiCROS system  101 , a microphone set is worn in/on both ears, and the receiver is worn on the better ear.  
         [0052]    Each instrument  16 A and  16 B has a molded shell  20 A,  20 B which is custom molded to fit each individual hearing aid wearer by known processes, such as making an impression of the individual hearing aid wearer&#39;s ear and forming the molded shell based on that impression. Each instrument 16A and  16 B also has a face plate  22 A,  22 B coupled to a circuit board (not shown) located inside the instrument  16 A and  16 B.  
         [0053]    Extending through each instrument  16 A and  16 B and specifically face plate  22 A,  22 B, is a battery door  26 A,  26 B, a volume control  28 A,  28 B, a switch S 1 A, S 1 B, a microphone mic FA, FB, and a microphone mic BA, BB. The battery door  26 A,  26 B allows the hearing aid wearer access to the instrument  16 A or  16 B for changing the battery (not shown). The volume control  28 A,  28 B allows the hearing aid wearer to adjust the volume or amplification of the instrument  16 A or  16 B.  
         [0054]    Switch S 1 A, S 1 B extends through the face plate  22 A,  22 B, and allows the hearing aid wearer to manually switch the instrument  16 A and  16 B between a non-directional or directional hearing aid mode. Switch S 1 A, S 1 B is electronically coupled to the circuit contained within the instrument  16 A or  16 B. With the novel idea of switch S 1 A, S 1 B, a hearing aid wearer can switch to a non-directional hearing aid mode to hear sounds from all directions, or a directional hearing aid mode, such as for reducing background noise when carrying on a conversation in a crowded room.  
         [0055]    Microphone mic FA, FB and microphone mic BA, BB in instrument  16 A and  16 B include inlet tubes  30 A,  30 B and  32 A,  32 B which protrude through the instrument face plate  22 A,  22 B. Microphone pairs mic FA and BA in instrument  16 A and microphone mic FB and BB in instrument  16 B are spaced a relatively short distance apart, preferably less than ½ inch. In one preferred embodiment, microphone pair mic FA and BA in instrument  16 A and microphone pair mic FB and BB in instrument  16 B are preferably ⅓ of an inch apart.  
         [0056]    An axis of directionality is defined by a line drawn through the inlet tube  30 A,  30 B and inlet tube  32 A,  32 B in face plate  22 A,  22 B, indicated at  34 . The instrument  16 A and  16 B in accordance with the present invention is of a molded design such that the axis of directionality  34  is relatively horizontal to the floor when the instrument is positioned within the hearing aid wearer&#39;s ear. With this design, optimum performance of the hearing aid system is achieved.  
         [0057]    The combination of a switched directional/non-directional microphone system in a custom in-the-ear CROS or BiCROS hearing aid system as illustrated in FIG. 6 will result in a significant improvement in signal to noise ratio for individuals in noisy listening situations.  
         [0058]    Referring now to FIG. 7, a polar directivity pattern  110  is shown for a BiCROS hearing aid system, with both instruments  16 A and  16 B switched into directional mode. The pattern was obtained on an HA-1 2 cc coupler in an anechoic chamber. The polar directivity pattern  110  shows the amount of pickup at a specific frequency (in this case,  1 K) of a BiCROS directional hearing aid system as a function of azimuth angle of sound incidence. In the illustrated pattern, the Directivity Index (DI-the ratio of sounds incident straight ahead to those incident all around an imaginary sphere) was 10.1 dB and the Unidirectional Index (UDI-the ratio of sounds incident on an imaginary front hemisphere to those from an imaginary rear hemisphere) was 5.0 dB. This polar pattern  110  indicates that sounds incident from the sides and rear will be significantly attenuated. The DI predicts up to a 10 dB improvement in signal-to-noise ratio, depending upon the amount of reverberation in the listening environment.  
         [0059]    Referring to FIG. 8, a block diagram showing the BiCROS, in-the-ear directional hearing aid system in accordance with the present invention is illustrated. In this embodiment, each of the two instruments of the hearing aid has its own microphone system. The directional microphone system  36 A,  36 B within each of the two instruments utilizes two non-directional microphone circuits  38 A,  40 A and  38 B,  40 B to achieve a directional microphone signal. Each directional microphone system  36 A,  36 B includes a first non-directional microphone system  38 A,  38 B and a second non-directional microphone system  40 A,  40 B. The output signals from the second non-directional microphone system  40 A,  40 B (indicated by signal  42 A,  42 B) may be electrically coupled through switch S 1 A and S 1 B, and summed at node  46 A,  46 B with the first non-directional microphone system  38 A,  38 B (indicated by signal  44 A,  44 B). The resulting output signal from each of the instruments is indicated at  48 A,  48 B. The output signal  48 A,  48 B from each of the instruments is coupled to a hearing aid circuit  50 . For example, the hearing aid circuit may be a linear circuit, a compression circuit, an adaptive high-pass filter, and may include a high-power output stage.  
         [0060]    Each of the two instruments  16 A and  16 B may be switched between a non-directional mode and a directional mode through the operation of switch S 1 A, S 1 B. In the non-directional mode, switch S 1 A, S 1 B is open (as shown), and non-directional microphone mic F  38 A,  38 B feeds directly into hearing aid circuit  50 . For operation in a directional mode, switch S 1 A, S 1 B is closed, and the first non-directional microphone system  38 A,  38 B and second non-directional microphone system  40 A,  40 B output signals are summed at summing node  46 A,  46 B, with the resulting output signal  48 A,  48 B being coupled to hearing aid circuit.  
         [0061]    In one embodiment, the second non-directional microphone system  40 A,  40 B of each instrument  16 A and  16 B includes non-directional microphone mic B, an inverter  52 A,  52 B, an adjustable phase delay  54 A,  54 B, and an adjustable gain  56 A,  56 B. The output signal of microphone mic B is coupled to inverter  52 A,  52 B, indicated at  58 A,  58 B. The output signal of inverter  52 A,  52 B is coupled to the adjustable phase delay  54 A,  54 B, indicated at  60 A,  60 B. The output of the adjustable phase delay  54 A,  54 B is coupled to the adjustable gain  56 A,  56 B, indicated at  62 A,  62 B. The output of the adjustable gain  56 A,  56 B is coupled to switch S 1 A, S 1 B, indicated at  64 A,  64 B.  
         [0062]    The output signal of microphone mic B in each of the instruments  58 A,  58 B is inverted by inverter  52 A,  52 B. Further, the adjustable phase delay  54 A,  54 B may adjust the phase delay of the output of mic B relative to the output of microphone mic F in each of the instruments. Similarly, adjustable gain  56 A,  56 B adjusts the amplitude of the output signal received from mic B relative to the output signal from microphone mic F. By providing such an adjustment, the hearing aid manufacturer may vary the polar directivity pattern of each instrument.  
         [0063]    The output signal  48 A,  48 B from first non-directional microphone system  38 A,  38 B and second non-directional microphone system  40 A,  40 B in each of the instruments may be amplified by passing it through amplifier  66 A,  66 B. The resulting output signal of amplifier  68 A,  68 B in each of the instruments  16 A and  16 B, is coupled to the hearing aid circuit  50 .  
         [0064]    As mentioned above, in a CROS system (not illustrated), the instrument in the better ear will not contain the microphone mic B or the microphone mic F, as shown in the illustrated BiCROS system.  
         [0065]    Referring to FIG. 9, a schematic diagram of one preferred embodiment of a BiCROS, in-the-ear hearing aid system with switched directional/non-directional microphone is shown. This hearing aid system has two instruments  16 A and  16 B. The first instrument  16 A, is designed to be placed in the individual&#39;s unaidable ear. The second instrument  16 B, having hearing aid amplifier  120 , is designed to be placed in the individual&#39;s better ear. A connection  102  for transmitting a signal from the first instrument  16 A to the second instrument  16 B may be made in a variety of ways, including a hard wire (illustrated), a RF transmission from the first instrument to the second instrument (not illustrated), or an induction transmission as in the Telex Wireless CROS system (not illustrated).  
         [0066]    In the first instrument  16 A, non-directional microphone mic F 1  has a coupling capacitor C 6 A coupled to its output. Resistor R 7 A is electrically coupled between coupling capacitor C 6 A and node  74 A. Non-directional microphone mic B 1  has a coupling capacitor C 7 A coupled to its output. Coupled to the output of C 7 A is inverter  52 A with adjustable phase delay  54 A. The inverter  52 A is an operational amplifier OPAMP  4 , shown in an inverting configuration. Coupled between capacitor C 7 A and the input node  70 A of OPAMP  4  is resistor R 11 A. Coupled between OPAMP  4  input node  70 A and an OPAMP  4  output node  72 A is resistor R 12 A. Similarly, coupled between OPAMP  4  input node  70 A and OPAMP  4  output node  72 A is capacitor C 8 A.  
         [0067]    As previously described herein, OPAMP  4  inverts the output signal received from non-directional microphone mic B 1 . As such, when the output signal  42 A and output signal  44 A are summed at summing node  46 A, the signals are subtracted, resulting in output signal  48 A.  
         [0068]    The gain between the input of OPAMP  4  and the output of OPAMP  4  is indicated by the relationship R 12 A/R 11 A. In one preferred embodiment, R 12 A equals R 11 A, resulting in a unity gain output signal from OPAMP  4 .  
         [0069]    The adjustable phase delay capacitor C 8 A may be adjustable. By adjusting capacitor C 8 A, the phase delay of the non-directional microphone mic B 1  output relative to the non-directional microphone mic F 1  may be adjusted. Coupled to the output node  72 A of OPAMP  4  is a resistor R 9 A in series with an adjustable resistor or potentiometer R 10 A. Further, coupled to output signal  72 A is an inverting operational amplifier, OPAMP  3  having an input node  74 A and an output node  76 A. Coupled between the input node  74 A and the output node  76 A is a resistor R 8 A. Also coupled between the input node  74 A and the output node  76 A is a capacitor C 5 A. It is recognized that capacitor C 5 A and resistor R 8 A may also be adjustable.  
         [0070]    When switch S 3 A is open, the resulting amplification or gain from the output from non-directional microphone mic F 1  is the ratio of resistors R 8 A/R 7 A. When switch S 3 A is closed, the output gain contribution from mic B 1  is determined by the ratio of R 8 A/(R 9 A plus R 10 A). By adjusting the adjustable potentiometer R 10 A, the amplitude of non-directional microphone mic B 1  of the output signal relative to the output signal amplitude of non-directional microphone mic F 1  may be adjusted. As previously stated herein, by adjusting both capacitor C 8 A and resistor R 10 A, the hearing aid may be adjusted to vary the polar directivity pattern of the in-the-ear hearing aid to account for component tolerances.  
         [0071]    In one known embodiment, the values for the circuit components shown in FIG. 9 are as follows:  
                       TABLE 2                                        C6A = .01 uF            C7A = .01 uF            C8A = .0022 uF            C5A = 110 pF            R7A = 10 K           R11A = 10 K           R12A = 10 K            R8A = 1 M            R9A = 10 K           R10A = 2.2 K                      
 
         [0072]    Non-directional microphone mic F 1  and non-directional mic B 1  can be non-directional microphones as produced by Knowles No. EM5346. Operational amplifiers OPAMP  3  and OPAMP  4  may be inverting Gennum Hearing Aid Amplifiers No. ¼ LX509.  
         [0073]    In the second instrument  16 B, non-directional microphone mic F 2  has a coupling capacitor C 1 B coupled to its output. Resistor R 5 B is electrically coupled between coupling capacitor C 1 B and node  74 B. Non-directional microphone mic B 2  has a coupling capacitor C 2 B coupled to its output. Coupled to the output of C 2 B is inverter  52 B with adjustable phase delay  54 B. The inverter  52 B is an operational amplifier OPAMP  1 , shown in an inverting configuration. Coupled between capacitor C 2 B and the input node  70 B of OPAMP  1  is resistor R 1 B. Coupled between OPAMP  1  input node  70 B and an OPAMP  1  output node  72 B is resistor R 2 B. Similarly, coupled between OPAMP  1  input node  70 B and OPAMP  1  output node  72 B is capacitor C 3 B.  
         [0074]    As previously described herein, OPAMP  1  inverts the output signal received from non-directional microphone mic B 2 . As such, when the output signal  42 B and output signal  44 B are summed at summing node  46 B, the signals are subtracted, resulting in output signal  48 B.  
         [0075]    The gain between the input of OPAMP  1  and the output of OPAMP  1  is indicated by the relationship R 2 B/R 1 B. In one preferred embodiment, R 2 B equals R 1 B, resulting in a unity gain output signal from OPAMP  1 .  
         [0076]    The adjustable phase delay capacitor C 3 B may be adjustable. By adjusting capacitor C 3 B, the phase delay of the non-directional microphone mic B 2  output relative to the non-directional microphone mic F 2  may be adjusted. Coupled to the output node  72 B of OPAMP  1  is a resistor R 3 B in series with an adjustable resistor or potentiometer R 4 B. Further, coupled to output signal  72 B is an inverting operational amplifier, OPAMP  2  having an input node  74 B and an output node  76 B. Coupled between the input node  74 B and the output node  76 B is a resistor R 6 B. Also coupled between the input node  74 B and the output node  76 B is a capacitor C 4 B. It is recognized that capacitor C 4 B and resistor R 6 B may also be adjustable.  
         [0077]    When switch S 4 B is open, the resulting amplification or gain from the output from non-directional microphone mic F 2  is the ratio of resistors R 6 B/R 5 B. When switch S 4 B is closed, the output gain contribution from mic B 2  is determined by the ratio of R 6 B/(R 3 B plus R 4 B). By adjusting the adjustable potentiometer R 4 B, the amplitude of non directional microphone mic B 2  of the output signal relative to the output signal amplitude of non-directional microphone mic F 2  may be adjusted. As previously stated herein, by adjusting both capacitor C 3 B and resistor R 4 B, the hearing aid may be adjusted to vary the polar directivity pattern of the in-the-ear hearing aid to account for component tolerances.  
         [0078]    In one known embodiment, the values for the circuit components shown in FIG. 9 are as follows:  
                       TABLE 3                                       C1B = .01 uF           C2B = .01 uF           C3B = .0022 uF           C4B = 110 pF           R5B = 10 K           R1B = 10 K           R2B = 10 K           R6B = 1 M           R3B = 10 K           R4B = 2.2 K                      
 
         [0079]    Non-directional microphone mic F 2  and non-directional mic B 2  can be non-directional microphones as produced by Knowles No. EM5346. Operational amplifiers OPAMP  1  and OPAMP  2  may be inverting Gennum Hearing Aid Amplifiers No. ¼ LX509.  
         [0080]    The hearing aid in accordance with the present invention allows a person wearing a BiCROS in-the-ear hearing aid to switch between a non-directional mode and a directional mode by simple operation of switch S 3 A in the first instrument  16 A and switch S 4 A in a second instrument  16 B. The circuit components which make up the directional microphone system are all located within the hearing aid housing and coupled to the inside of face plate. Further, by adjustment of the adjustable phase delay and adjustable gain, the directional microphone system may be adjusted to vary the polar directivity pattern to account for component tolerances. It is also recognized that capacitor C 5 A and resistor R 8 A in the first instrument  16 A and capacitor C 4 B and resistor R 6 B in the second instrument  16 B may be adjustable to compensate for each individual&#39;s hearing loss situation.  
         [0081]    It will be understood that this disclosure is, in many respects, only illustrative. Changes may be made in details, particularly in matters of shape, size, material, and arrangement of parts, without exceeding the scope of the invention. Accordingly, the scope of the invention is as defined in the language of the appended claims.