Patent Publication Number: US-6704423-B2

Title: Hearing aid assembly having external directional microphone

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application makes reference to, and claims priority to, United States provisional application Ser. No. 60/173,427 filed Dec. 29, 1999. 
    
    
     INCORPORATION BY REFERENCE 
     The above-referenced United States provisional application Ser. No. 60/173,427 is hereby incorporated herein by reference in its entirety. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     N/A 
     BACKGROUND OF THE INVENTION 
     Numerous types of hearing aids are known and are currently in use. Hearing aid users generally prefer hearing aid types that are minimally visible to third parties, but provide maximum performance in noisy environments. One common hearing aid type is worn behind-the-ear (BTE) and is quite visible to third parties. Such BTE hearing aids also generally do not perform well in noisy environments. For example, typical BTE hearing aids demonstrate Articulation-Index-weighted average Directivity Index (AIDI) values in the range of 2-3 dB (due to the high frequency shadowing of the Pinna, or earflap). For many users, BTE hearing aids simply do not provide the directivity performance sufficient to make the BTE viable in noisy environments. 
     In-the-ear (ITE) hearing aid solutions that are less visible and also provide improved performance in noisy environments have therefore been developed using directional microphone technology. One directional microphone for ITE applications is the D-MIC® of Etymoic Research, Inc. The D-MIC® directional microphone in an ITE hearing aid provides typical AIDI values in the range of 5+dB, a substantial improvement over BTE applications. 
     Despite the fact, however, that ITE hearing aids as such are less visible and provide substantial improvement in directivity performance, ITE hearing aids still require that the entire concha of the wearer&#39;s ear be filled, and that the directional microphone be located on the near flat outer surface of the hearing aid. Such an arrangement is still quite visible. 
     Consequently, even less visible hearing aids have been developed for in the ear applications, namely in the canal (ITC) and completely in the canal (CIC) hearing aids. ITC and CIC hearing aids are discreetly located in the resonant portion of the ear canal, and thus do not require that the entire concha of the ear be filled. Hearing aid wearers, therefore, generally prefer the less visible ITC and CIC hearing aids over ITE hearing aids. 
     ITC and CIC hearing aids, however, do not perform as well as ITE hearing aids, or even BTE hearing aids, in noisy environments. Directional microphones simply do not provide useful directionality in ITC and CIC hearing aid applications because of the location of the hearing aid in the resonant portion of the wearer&#39;s ear canal. The sound field at such a location has no detectable frequency dependent phase shift as is found in free space or on a surface in free space (as with an ITE hearing aid). Currently available ITC and CIC hearing aids therefore use only omni-directional microphones, and provide typical AIDI values in the range of −0.5 to 0.2 dB. Such directionality performance is not adequate for most users in noisy environments. 
     It is thus an object of the invention to provide the improved directionality performance similar to ITE solutions for the less visible ITC and CIC hearing aids. 
     It is a further object of the invention to provide the improved directionality performance similar to ITE solutions for BTE hearing aids with little or no visual impact or prior art BTE hearing aid designs. 
     It is still a further object of the invention to provide an overall improved directivity performance for ITE hearing aid applications. 
     BRIEF SUMMARY OF THE INVENTION 
     These and other objects of the invention are achieved in a microphone system having a hearing aid housing and a directional microphone mounted externally to the hearing aid housing. A link operatively couples the directional microphone to a component, such as, for example, a hearing aid amplifier or speaker, located internally to the hearing aid housing. The link may also be configured to mechanically mount the directional microphone to an external surface of the hearing aid housing, which surface may be, for example, a hearing aid faceplate. 
     In one embodiment, the link is a mounting arm that effectively mounts the directional microphone to a hearing aid faceplate and enables electrical connection of the directional microphone to the component within the hearing aid housing. For example, the mounting arm may be a rigid tube that mounts the directional microphone on one and is mounted to a faceplate on the other. Wires connecting the directional microphone to the internal component may therefore travel through the tube and faceplate. 
     The directional microphone may be configured externally to the hearing aid housing such that, when the hearing aid housing is inserted into the ear of a wearer, the microphone is located between the helix and tragus portions of the ear. 
     The directional microphone may comprise a directional microphone cartridge having a front inlet tube and a rear inlet tube both operatively coupled to the microphone cartridge. In one embodiment, the front tube is empty. In another embodiment, an acoustical impedance, such as, for example, a plurality of rods are placed longitudinally in the front inlet tube to improve the polar performance of the directional microphone. The rods may be, for example, monofilament fishing line. 
    
    
     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 is a block diagram of a hearing aid assembly of the present invention. 
     FIG. 2 is one embodiment of the hearing aid assembly of the present invention for ITC and CIC hearing aid applications. 
     FIG. 3 is another embodiment of the hearing aid assembly of the present invention for BTE hearing aid applications. 
     FIG. 4 illustrates an exploded side view of one embodiment of a directional microphone assembly for use in the hearing aid assembly embodiments of FIGS. 2 and 3. 
     FIG. 5 is an end view of the front tube portion of the microphone assembly of FIG. 4 having rods placed longitudinally in the front tube portion. 
     FIG. 6 is a plot of the frequency response for each of the directional microphone assembly embodiments of FIGS. 4 and 5. 
     FIG. 7 illustrates plots of the polar response of the directional microphone assembly of FIG.  4 . 
     FIG. 8 illustrates plots of the polar response of the directional microphone assembly of FIG.  5 . 
     FIG. 9 depicts an upper mounting portion and tube portion of a link or mounting arm according to the present invention. 
     FIG. 10 illustrates the directional microphone assembly of FIG. 4 mounted in the upper mounting portion of FIG.  9 . 
     FIG. 11 illustrates a side cross-sectional view of one embodiment of connection of the link or mounting arm of FIG. 2 with a hearing aid faceplate. 
     FIG. 12 is a top view of one embodiment of an elbow and nut depicted in FIG.  11 . 
     FIG. 13 illustrates one embodiment of the hearing aid assembly of the present invention inserted into the ear canal of a wearer. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 is a block diagram of a hearing aid assembly of the present invention. Hearing aid assembly  1  comprises a hearing aid  3  that is mechanically and electrically connected to an external directional microphone  5  via a link  7 . Directional microphone  5  may be a first or higher order directional microphone. Directional microphone  5  may comprise, for example, a single directional microphone cartridge as shown in FIG. 1 or an array microphone as described in copending application Ser. No. 09/517,848 of Soede et al., which application is incorporated by reference herein in its entirety. Directional microphone  5  may also comprise a dual omnidirectional directional microphone. Directional microphone  5  may also incorporate an omni-directional microphone for switching between directional and omni-directional modes. Hearing aid  3  may be a BTE, ITE, ITC or CIC hearing aid, and may include internal components such as an amplifier  9  and a receiver  11 , as is known in the art. 
     During operation of the hearing aid assembly  1 , sound energy impinges on the externally located directional microphone  5 , and is transduced by the directional microphone  5  into electrical signals. The electrical signals are then transmitted to the hearing aid  3  via the link  7 , where the signals are amplified by the amplifier  9 , transduced to sound energy by the receiver  11 , and then transmitted into the ear canal of a wearer. 
     FIG. 2 is one embodiment of the hearing aid assembly of the present invention for ITC and CIC hearing aid applications. Hearing aid assembly  13  comprises a directional microphone  15  that is mechanically and electrically connected to an ITC hearing aid  17  via link (or mounting arm)  19 . Alternatively, directionally microphone  15  is mechanically and electrically connected to a CIC hearing aid  21  (shown smaller by a dotted outline) via the links  19 . As can be seen, the CIC hearing aid  21 , as well as the additional length of the link  19  needed for the location of the CIC hearing aid  21  further in the ear canal (relative to ITC hearing aid  17 ), are depicted by dashed lines. In either the ITC or CIC application, the directional microphone  15  is located, as generally shown in FIG. 2, in the notch between the helix  18  and tragus  20  portions of the ear, with a front sound inlet port  23  of the microphone  15  facing generally forward. 
     FIG. 3 illustrates another embodiment of the hearing aid assembly of the present invention for BTE hearing aid applications. Hearing aid assembly  25  comprises a directional microphone  27  that is electrically and mechanically connected to a BTE hearing aid body  29  via a link (or mounting arm)  31 . BTE hearing aid body  29  is also acoustically connected to an earmold  33  via a tube  35 . Connection between BTE hearing aid body  29  and tube  35  is not shown in FIG. 3 because the connection is located behind, and is obscured by, directional microphone  27  and link  31 . However, connection between BTE hearing aid bodies and earmolds are known in the art. 
     As can be seen from FIG. 3, the directional microphone  27  is located on the side of the head near the notch between the helix and tragus portions of the ear like the directional microphones in the embodiments illustrated in FIG.  2 . Such a location of the directional microphone provides the desired results, as will become more apparent below. However, other locations of the microphone are also possible, such as, for example, in the space  36  below the tragus of the ear. In general, acceptable results may be achieved by, for example, locating the directional microphone with the front sound entry port positioned over the occluded ear canal, and the rear sound entry port positioned approximately in the range of 4-9 millimeters toward the back of the head, in the “bowl” or concha  34  of the ear. 
     FIG. 4 illustrates an exploded side view of one embodiment of a directional microphone assembly for use in the hearing aid embodiments of FIGS. 2 and 3. Directional microphone assembly  37  comprises a directional microphone cartridge  39  having a front sound inlet port  41 , a rear sound inlet port  43  and electrical terminals  45 . The directional microphone cartridge may be, for example, a variation of a Model TM directional microphone cartridge available from Knowles Electronics. 
     Directional microphone assembly  37  further comprises a hollow tube  47 . Tube  47  may be, for example, #15 hypodermic tubing having an inner diameter of 0.054 inches, and may have, for example, an overall length of approximately 0.23 inches. Tube  47  has saddle notch  49  cut or formed therein, forming a front sound inlet tube portion  51  on the front end of the tube  47 , and a rear sound inlet tube portion  53  on the rear end of tube  47 . Saddle notch  49  may be, for example, 0.070 inches long (see dimension A in FIG.  4 ), front sound inlet tube portion  51  may be, for example, 0.110 inches long (see dimension B in FIG.  4 ), and rear sound inlet tube portion  53  may be, for example, 0.050 inches long (see dimension C in FIG.  4 ). While a notch  49  is shown in single tube  47  to form the tube portions  51  and  53  (for ease of assembly), it should be understood that two separate tubes could be attached on either side of microphone cartridge  39  to form front and rear sound inlets. 
     During assembly of the microphone assembly  37 , the microphone cartridge  39  is placed in the saddle notch  49  so that the front sound inlet port  41  communicates with the front sound inlet tube portion  51  of the tube  47 , and the rear sound inlet port  43  communicates with the rear sound inlet tube portion  53  of the tube  47 . Rear sound inlet tube portion  53  may also have an acoustic resistor  55  placed therein for determining, for example, the polar pattern of the directional microphone assembly  37 . Epoxy may also be used on surface(s) in the saddle notch  49  to seal around edges of tube portions  51  and  53  that mate with microphone cartridge  39 , to solidify the microphone assembly  37 . 
     In the embodiment of FIG. 4, front sound inlet tube portion  51  of the tube  47  is shown as an open tube. In an alternate embodiment, the microphone assembly of FIG. 4 may be modified by adding an acoustical impedance into the front sound inlet tube portion  51  to reduce its diameter and improve the polar performance of the directional microphone assembly. For example, a single sleeve, plural vinyl tubes, pieces of enameled wire, or rods may be placed in the front tube portion  51 . FIG. 5 is an end view of the front tube portion of the microphone assembly of FIG. 4 having  11  rods  57  placed longitudinally in the front tube portion  51 . The rods  57  may be, for example, 0.014 inch monofilament fishing line. 
     FIG. 6 is a plot of the frequency response for each of the embodiments of FIGS. 4 and 5. Curve  59  is the response for the embodiment of FIG. 4 (i.e., having an open front tube portion), and curve  61  is the response for the embodiment of FIG. 5 (i.e., having an acoustic impedance located in the front tube portion). A value of 1200 Ω was used for the acoustic resistor  55  in both embodiments. In the case of curve  61 , the  11  rods  57  of FIG. 5 are 0.014 inch monofilament fishing line. As can be seen in FIG. 6, the response curve  61  at 3-4 KHz is lower than response curve  59  by about 5 dB, and at 10 KHz is lower than response curve  59  by about 11 dB. Thus, the peak generated by the open tube arrangement is flattened or is rolled off by the addition of an acoustic impedance. While such a roll-off may not be desirable, the addition of the acoustic impedance improves the polar response of the directional microphone assembly. 
     More specifically, FIG. 7 illustrates plots of the polar response of the directional microphone assembly having an open tube arrangement as in FIG. 4, while FIG. 8 illustrates plots of the polar response of the directional microphone assembly of FIG. 4 having the rods of FIG.  5 . Again, a value of 1200 Ω was used for the acoustic resistor  55  in both embodiments. A comparison of FIGS. 7 and 8 shows that the directional microphone assembly having the acoustic impedance maintains its directionality better (longer) as the frequency increases. In addition, the directional microphone assembly having the acoustic impedance has a higher overall AIDI value (5.99 as compared to 5.33). In either embodiment, however, the AIDI values achieved are comparable to those achieved by prior art ITE hearing aids (mentioned above). 
     FIG. 9 depicts an upper mounting portion  63  and a tube portion  65  of the link  19  of FIG. 2 for mounting the directional microphone assembly of FIG.  4 . Upper mounting portion  63  may be formed by flattening and shaping a single tube (and thus creating the upper mounting portion  63  and tube portion  65 ). Upper mounting portion  63  comprises notches  67  that receive the front sound inlet tube portion  51  and the rear sound inlet tube portion  53  of the tube  47  when, upon assembly, the microphone cartridge  39  is seated within the upper mounting portion  63 . Tube portion  65  is hollow, so that electrical connection between the microphone cartridge  39  and the hearing aid amplifier can be made by wires running through the link  19 . 
     FIG. 10 illustrates the directional microphone assembly of FIG. 4 mounted in the upper mounting portion  63  (FIG. 9) of the link  19  of FIG.  2 . The microphone assembly as depicted in FIG. 4 has been rotated 90 degrees and mounted with the upper mounting portion  63 . Microphone cartridge  39  is seated within the upper mounting portion  63 , such that rear sound inlet tube portion  53  rests partially within a notch  67 . Front sound inlet tube portion  51  (not shown) likewise partially rests within a notch  67  (not shown) on the opposite side of the upper mounting portion  63 . Glue may be used to rigidly attach the directional microphone assembly and the upper mounting portion  63 . Each of the three electrical terminals  45  on the microphone cartridge  39  is connected to a wire, and the three wires  69  run through the tube portion  65  for electrical connection to the hearing aid amplifier or other hearing aid component(s) (not shown). 
     FIG.  11 . illustrates a side cross-sectional view of one embodiment of connection of the link (or mounting arm)  19  of FIG. 2 with a hearing aid faceplate  71  via an elbow  73 . For a right ear hearing aid model with mounting in the notch between the helix and tragus, the elbow  73  is, for example, approximately 90 degrees, and the link  19  is mounted generally parallel with the faceplate  71 . In addition, the microphone assembly  37  is mounted, for example, approximately 45 degrees to the faceplate  71 . 
     The link  19  is mounted within an opening in the elbow  73 . The length of the link  19  may be adjusted by moving the link  19  further into or out of the opening in the elbow, and the link  19  may then be glued in place. The length of the link  19  may also be adjusted further by bending it once it has been glued in place. The microphone assembly  37  may also be oriented by rotating the link  19  within the opening of the elbow  73  prior to application of the glue. 
     Elbow  73  is mounted on an outer surface  74  of faceplate  71  and includes a threaded stem  75  that passes through an opening  77  in the faceplate  71 . The threaded stem  75  mates with a nut  79 . When tightened, the nut  79  rests against an inner surface  80  of the faceplate  71  to firmly mount the elbow  73 , and thus the link  19 , on the hearing aid faceplate  71 . The threaded stem  75  is also hollow to allow the microphone wires to pass from the link  19  to the hearing aid amplifier or other hearing aid component(s) (not shown). 
     Elbow  73  may also include an omni-directional microphone  81  mounted in a recess in the elbow  73 . Wires from the omni-directional microphone  81  can likewise pass through the threaded stem  75  to the hearing aid amplifier or other hearing aid component(s) (not shown). Omni-directional microphone  81  may be, for example, a Model FG microphone from Knowles Electronics. 
     FIG. 12 is a top view of one embodiment of the elbow  73  and nut  79  of FIG.  11 . Elbow  73  includes an opening  83  for receiving the link or mounting arm  19 , as well as a recess  85  for receiving the omni-directional microphone  81 . Opening  83  may have, for example, a diameter of approximately 0.065 inches. From the location of the opening  83  and the recess  85  in FIG. 12, it appears that an interference may occur between the link  19  and omni-directional microphone  81  when they are respectively placed in the opening  83  and the recess  85 . However, this apparent interference may be resolved by notching the end of the link  19  inserted into the opening  83 . 
     As mentioned above, threaded stem  75  is hollow to enable wires to pass therethrough. The threaded stem may have, for example, an outer diameter of approximately 0.087 inches and an inner diameter of approximately 0.038 inches. Such an inner diameter enables  6  wires to fit through the threaded stem  75  (3 from the directional microphone cartridge and 3 from the omni-directional microphone). 
     Also as mentioned above, the threaded stem  75  mates with a nut  79  which, when tightened, rests against an inner surface  80  of the hearing aid faceplate  71 . To conserve space within the hearing aid, the nut  79  may be modified by cutting off portions  87  and  89  of the nut  79 . 
     FIG. 13 illustrates one embodiment of the hearing aid assembly of the present invention inserted into the ear canal of a wearer. As can be seen, when the hearing aid is seated in the ear canal, the directional microphone is located in the notch between the helix and tragus of the ear. It should be understood that the cable  91  and wire  93  shown in FIG. 13 exist solely for test and hearing aid removal purposes, respectively, and are not a necessary part of the operable device. The mounting arm  19  may instead be used as a lever for insertion and removal of the hearing aid. 
     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.