Abstract:
An exemplary method includes an electro-acoustic stimulation (EAS) system associated with a user 1) processing sounds sensed by a first microphone coupled to a cochlear implant portion of the EAS system, 2) applying electrical stimulation representative of the sounds sensed by the first microphone by way of a plurality of electrode contacts located in a basal region of a cochlea of the user, 3) processing sounds sensed by a second microphone coupled to a hearing aid portion of the EAS system, 4) broadcasting, way of a speaker, amplified sound signals representative of the sounds sensed by the second microphone into an ear canal of the user, and 5) acoustically separating the second microphone from the speaker to avoid feedback within the hearing aid portion of the EAS system. Corresponding methods and systems are also disclosed.

Description:
RELATED APPLICATIONS 
     The present application is a continuation application of U.S. patent application Ser. No. 12/584,306 by Matthew I. Haller, filed on Sep. 3, 2009, and entitled “Dual Microphone EAS System That Prevents Feedback,” which application is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND INFORMATION 
     The present invention relates to hearing aid systems, and more particularly to a hybrid or Electro Acoustic Stimulation (EAS) hearing aid system that combines a cochlear stimulator and a hearing aid to provide a hearing aid system that relies primarily on the cochlear stimulator portion of the system for being able to sense high frequency sounds, and that relies primarily on normal hearing processes, assisted as required by a hearing aid, for being able to sense lower frequency sounds. A representative hybrid or EAS hearing system is described, e.g., in U.S. Pat. No. 6,754,537, incorporated herein by reference in its entirety. 
     A hybrid or EAS hearing aid system, such as is disclosed in U.S. Pat. No. 6,754,537, is best suited for use with a short cochlear electrode array of the type described in U.S. Pat. No. 6,889,094 entitled “Electrode Array for Hybrid Cochlear Stimulator”, or equivalent short, atraumatic lead. U.S. Pat. No. 6,889,094 is incorporated herein by reference. 
     A hybrid or EAS cochlear stimulation system provides electrical stimulation only to the basal end of the cochlea to stimulate ganglion cells responsible for sensing higher-frequency sounds, and relies on normal or assisted hearing (activation of hair cells through fluid motion within the cochlea), which may occur with or without the assistance of a conventional or a custom hearing aid, to sense middle-to-lower frequency sounds. 
     A common problem that plagues hearing aid users is feedback. Feedback occurs in an acoustic amplification system, such as a hearing aid system, when the amplified sound is picked up by the microphone, causing the amplification system to become unstable and squeal. The best way to eliminate feedback is to acoustically separate the microphone from the hearing aid “speaker”, or electrical-to-acoustic transducer used to broadcast amplified audio signals against the user&#39;s ear drum. However, despite efforts to seal the ear canal (e.g., by preparing an ear mold designed to fit tightly in the ear canal with the microphone held on the side of the mold facing the outside of the ear, and the speaker held on an opposite side of the mold facing the ear drum, with the intent of acoustically separating the speaker from the microphone), some acoustic sound waves broadcast from the speaker always seem to leak back to the microphone, where they are sensed by the microphone, causing the hearing aid system to become unstable and squeal. 
     Thus, it is seen that there is a need in the art for eliminating feedback in a hearing aid system, and more particularly for eliminating feedback in an EAS hearing prosthesis system utilizing both a cochlear implant for allowing a user to perceive high frequency sound, and a conventional hearing aid for allowing the user to hear low frequency sound. 
     SUMMARY 
     The present invention addresses the above and other needs by providing an electro-acoustic stimulation (EAS) system that includes both a hearing aid adapted to sense and amplify low frequency acoustic sound signals and a cochlear implant (CI) adapted to sense high frequency acoustic sound signals. The hearing aid portion of the EAS system has a first microphone adapted to sense low frequency acoustic sound signals, amplify these sensed low frequency acoustic sound signals, and present the resulting amplified low frequency acoustic sound signals in the ear canal of a user, thereby enabling the user to better hear these amplified sounds using his or her normal hearing processes. The cochlear implant portion of the EAS system includes a second microphone adapted to sense the high frequency acoustic sound signals and selectively stimulate the inner ear with electrical stimulation that will be perceived as high frequency acoustic sound signals. 
     In most instances, both the cochlear implant portion and the hearing aid portion of the EAS system operate on the same ear of the user. For a bilateral EAS system, a respective cochlear implant portion and hearing aid portion could be used in each ear. In some situations, it may be desirable to configure the cochlear implant portion to operate in one ear, and to configure the EAS system to operate in the other ear. 
     Advantageously, in accordance with the teachings provided herein, feedback within the hearing aid portion of the EAS system is eliminated by positioning the first microphone at a location that is acoustically remote from the ear canal where the amplified low frequency acoustic sound signals are presented. In contrast, high frequency acoustic sound signals are better sensed through the CI portion of the EAS system by placing the second microphone at a location that is in or near the ear canal where the amplified low frequency acoustic sound signals are presented. 
     It is a feature of the present invention to provide a dual microphone EAS system wherein undesirable feedback is eliminated in the hearing aid portion of the EAS system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features and advantages of the present invention will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings wherein: 
         FIG. 1  is a functional schematic diagram of the ear, showing the manner in which an implantable cochlear stimulator and short cochlear electrode array in the basal region of the cochlea may be used to aid a user to better perceive high frequency sound while preserving residual hearing for perceiving low frequency sound; 
         FIG. 2  is a functional schematic diagram of the ear as in  FIG. 1 , and further shows the manner in which a conventional in-the-ear hearing aid may be used to supplement the manner in which low frequency sounds are perceived; 
         FIG. 3A  shows the external components of one preferred embodiment of an EAS system wherein two microphones are used; 
         FIG. 3B  is a functional block diagram of the sound processing portion of a two microphone EAS system; 
         FIG. 3C  is a functional schematic diagram of the ear as in  FIGS. 1 and 2  and further shows one embodiment of an EAS system wherein two microphones are employed; 
         FIG. 4A  is a block diagram that depicts an EAS system using multiple microphones, wherein the microphone(s) associated with the hearing aid portion are positioned to eliminate feedback, and further wherein the speaker associated with the hearing aid portion is positioned near the front end of the ear canal; and 
         FIG. 4B  is a block diagram that depicts an EAS system using multiple microphones, as in  FIG. 4A , but wherein the speaker associated with the hearing aid portion is positioned in the ear canal of the user, closer to the ear drum. 
     
    
    
     Corresponding reference characters indicate corresponding components throughout the several views of the drawings. 
     DETAILED DESCRIPTION 
     The following description is of the best mode presently contemplated for carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of describing the general principles of the invention. The scope of the invention should be determined with reference to the claims. 
     Turning first to  FIG. 1 , a system is depicted that uses electrical stimulation of the inner ear to enhance the perception of high frequency sounds, and residual hearing to sense low frequency sounds. The description of this hybrid system (using both electrical stimulation and residual hearing) is presented as background to better understand the operation of the dual microphone EAS system described in more detail below. 
     As seen in  FIG. 1 , the major relevant components of the outer, middle and inner ear are illustrated. To better understand the present invention, it will first be helpful to briefly review the normal operation of a fully functional ear. Thus, as seen in  FIG. 1 , the outer ear includes the auricle  14  and the ear canal  16 . An acoustic pressure wave, or sound wave, represented in  FIG. 1  by short, spaced-apart, arc lines  12 , is collected by the auricle  14  and funneled into the ear canal  16 . At the end of the ear cannel  16  is the “ear drum”  18 , or in medical terms, the tympanic membrane  18 . In a person who is not significantly hearing impaired, the received acoustic wave  12  causes the tympanic membrane  18  to vibrate, which vibration is coupled through three tiny bones, the malleus (“hammer”)  20 , the incus (“anvil”)  22  and the stapes (“stirrup”)  24 , to the fenestra  30 . (In anatomical terms, the fenestra comprises an opening resembling a window. The fenestra ovalis, or oval window, is the opening between the middle ear and the vestibule of the inner ear. It is closed by a membrane to which the stapes is attached. The fenestra rotunda, or round window, is the opening between the scala tympani of the cochlea and the middle ear. The round window is also closed by a membrane, which for purposes of the present application, may be referred to as the basal membrane. For purposes of the schematic diagram shown in  FIG. 1 , as well as the other figures presented herein, the function of both the oval window and round window is represented by the single membrane  30 .) 
     The bones of the middle ear serve to filter and amplify the perceived acoustic wave  12 , causing the fenestra membrane  30  to articulate, or vibrate, in response to the acoustic wave  12 . Vibration of the membrane  30  sets up waves of fluid motion within the fluid contained within the snail-shaped cochlea  36 . Such fluid motion, in turn, activates tiny hair cells (not shown in  FIG. 1 ) that line the inside of the cochlea  36 . Activation of the hair cells causes appropriate nerve impulses to be transferred through the spiral ganglion  40  to the brain, where they are perceived as sound. 
     The spiral ganglion cells that are responsible for the perception of high frequency sounds are generally located at the basal end of the cochlea  36 , i.e., that end of the cochlea closest to the membrane  30 . For those individuals who suffer from high frequency hearing loss, the hair cells in the basal region of the cochlea are ineffective or otherwise damaged to the point where it is not possible to activate them with fluid motion within the cochlea. Hence, to overcome this high-frequency hearing deficiency, an implantable cochlear stimulator (ICS)  50  may be implanted near the ear, and a short cochlear electrode array  52 , having a plurality of spaced apart electrodes  54  thereon, is inserted into the cochlea  36  through the membrane  30 . (In practice, the electrode array  52  may be inserted directly through a slit made in the round window, or it may be inserted through tissue near the round window.). 
     The ICS  50  is coupled to external components  39 , which include a microphone  40 , a speech processor  42  and a headpiece  43 . Coupling with the ICS may occur through various means, but is usually achieved through an rf and/or electromagnetic coupling link  44  established between an implanted coil located in the ICS, and a coil located in the external head piece  43 , connected to the wearable sound processor  42  (or a behind-the-ear (BTE) processor). Such link  44  also provides a way for power to be coupled into the implanted ICS  50 . In practice, control signals are typically coupled through the link  44  via radio frequency waves transmitted from an antenna coil in the headpiece  43  to a receiving coil located in the ICS  50 . Power is typically coupled through the link  44  via inductive coupling that occurs between the antenna coil located in the headpiece  43  and an implanted coil located in the ICS  50 . It is to be noted, that in some embodiments, it is possible for the processor and power source to be implanted, either as an integral part of the ICS  50  or in a separate housing coupled to the ICS. (See, e.g., U.S. Pat. No. 6,272,382 or U.S. Pat. No. 6,308,101, incorporated herein by reference.) 
     In operation, the speech processor  42  functions as a signal processing means for processing the electrical signals received from the microphone  40  and for generating high frequency control signals therefrom representative of the higher frequency content of the sensed acoustic sounds. These control signals are then coupled to the ICS  50  through the link  44 . The ICS  50  has means responsive to the high frequency control signals for selectively generating electrical stimuli and applying the electrical stimuli to the electrode contacts  54  located at or near the distal end of the electrode  52 . In this manner, the basal region of the scala tympani duct is stimulated with electrical stimuli representative of the higher frequency content of the sensed acoustic sounds. 
     In accordance with the configuration depicted in  FIG. 1 , the sounds sensed by the microphone  40  are processed and filtered to separate out the high frequency sounds. These high frequency sounds are then converted to appropriate electrical stimuli that are selectively applied to the electrode contacts  54  of the electrode array  52  positioned in the basal region of the cochlea. Such electrical stimuli bypass the defective hair cells in the basal region of the cochlea and directly activate the nerves within the of the spiral ganglion, causing nerve impulses to be transferred to the brain, where they may be perceived as high frequency sounds. 
     The other hair cells in the cochlea, i.e., those in the apical and mid regions of the scala tympani duct, retain their functionality. That is, these hair cells are able to sense the fluid waves set up by vibrations of the membrane  30  corresponding to low-to-mid frequency sounds. Hence, the patient (or user of the hybrid system shown in  FIG. 1 ) is able to sense high frequency sounds through the ICS portion of the system, and is able to sense lower frequency sounds through the normal hearing processes of the ear. 
     In  FIG. 2 , another configuration of an EAS system is depicted. The configuration shown in  FIG. 2  is the same as the configuration shown in  FIG. 1  except for the addition of an in the canal hearing aid  15 . The in the canal hearing aid  15 , which may be of conventional design, senses the acoustic waves  12  through a microphone  17 , amplifies the signal, and rebroadcasts the signal through an electrical-to-acoustic transducer (or “speaker”)  19  as amplified acoustic waves  13 . These amplified acoustic waves  13  are directed to the tympanic membrane (or eardrum)  18  located at the end of the ear canal  16 . The amplified acoustic waves  13  are thereby able to increase the magnitude of the vibrations that pass through the middle ear and articulate the membrane  30 , thereby increasing the magnitude of the fluid waves within the cochlea, which higher magnitude fluid waves may be more effective at activating the hair cells throughout the cochlea. Typically, however, the high frequency hair cells at the basal end of the cochlea remain defective and unresponsive to the higher magnitude fluid waves. Thus, the cochlear stimulator portion (ICS  50  and electrode array  52 ) of the hybrid system must still be used if high frequency sounds are to be perceived. 
     Next, with reference to  FIG. 3A , the external components of one preferred embodiment of an EAS system are depicted. These external components include a first microphone  40  and a second microphone  41 . The first microphone  40  is located at the end of a flexible boom  48  attached to an ear hook of a behind-the-ear (BTE) unit  49 . When the BTE unit  49  is placed over the ear, the boom  48  advantageously positions the microphone  40  at a location where sound collected by the auricle  14  (see  FIG. 1 ) is focused, near the opening of the ear canal  16 . 
     Also located near the opening of the ear canal  16  is a speaker  19  that is oriented to direct the sound emitted therefrom towards or in the ear canal  16 . 
     A key feature of the EAS system described herein is that the sounds sensed by the microphone  40  are not the same sounds that are processed and amplified and then emitted from the speaker  19 . Rather, the sounds sensed by the microphone  40  are limited to the higher frequency sounds, e.g., sounds associated with frequencies above a frequency f H , where f H  is typically in the range of 800-1000 Hz. These higher frequency sounds are processed by the BTE unit  49 , which includes a speech processor  42  as described elsewhere herein. 
     The speech processor  42  converts the sensed higher-frequency signals to corresponding control signals that are coupled to a cochlear implant (not shown in  FIG. 3A , but described in connection with the other figures). The cochlear implant, responsive to these control signals, generates electrical stimulus signals which are selectively applied to electrode contacts  54  of an implantable electrode array  52 , as described previously in connection with  FIG. 1 . These stimulus signals, in turn, activate spiral ganglion cells located near the electrodes, thereby allowing the user to perceive these stimulus signals as the higher-frequency sound which the user otherwise would not be able to perceive. 
     The second microphone  41  is positioned at a location that is acoustically remote from the speaker  19 . One preferred location for the microphone  41  is on the headpiece  43 . However, it is to be understood that the microphone  41  may be positioned at other locations as well. The headpiece  43 , in turn, is connected to the BTE unit  49  by way of a cable  47 . The sounds sensed through the second microphone  41  are limited to the lower and mid-range frequency sounds. Lower frequency sounds, for purposes herein, are sounds having a frequency less than f L , where f L  is typically in the range of 200-400 Hz. Mid-range frequency sounds, for purposes herein, are those sounds having a frequency f M , where f M  is between f L  and f H . These sounds are amplified by a suitable amplifier and/or other sound processing circuits contained with the BTE unit  49  and are presented to the speaker  19  located in or near the opening of the ear canal  16 . Because the sounds being emitted by the speaker  19  are different sounds than those sensed by the microphone  40 , no undesirable feedback is created. Thus, in this manner, the user is able to perceive and hear both low-to-mid range frequency sounds (as sensed through microphone  41  and amplified and presented to the user through his or her ear canal via speaker  19 ) as well as high frequency sounds (as sensed through microphone  40  and presented to the user through a cochlear implant system). 
     The signal processing that takes place in the BTE unit  49  is preferably done using digital circuits that allow a very sharp and precise frequency separation between the low-to-mid range frequency signals that are sensed through microphone  41  and those that are sensed through microphone  40 . This prevents undesirable feedback from occurring between the microphone  40  and the speaker  19 , which are in close proximity to each other. 
     Turning next to  FIG. 3B , one preferred embodiment of the functional signal processing portions of the EAS system described herein is shown. As seen in  FIG. 3B , there are at least two signal processing channels associated with the EAS system. Each channel employs a separate microphone (MIC). 
     As seen in  FIG. 3B , a first microphone  40  (MIC1) is coupled to a first pre-amplifier  60  (Pre-Amp1), the output of which is directed as an input signal to a first analog-to-digital converter  61  (A/D1). The output digital signals from A/D1 are then directed to a first digital filter  64  (DF1), where only the higher frequency signals, i.e., those above frequency f H , are selected for further processing by Processor  66 . These higher frequency signals are processed by the Processor  66  and converted to appropriate control signals. These control signals are directed to the cochlear implant (CI) in order to allow the CI to electrically stimulate the appropriate areas of the basal region of the cochlea, thereby allowing the user to better perceive these higher frequency sound signals. As depicted in  FIG. 3B , these control signals are functionally directed to the CI over signal line  67 . 
     As further seen in  FIG. 3B , a second microphone  41  (MIC2) is coupled to a second pre-amplifier  62  (Pre-Amp2), the output of which is directed as an input signal to a second analog-to-digital converter  63  (A/D2). The output digital signals from A/D2 are then directed to a second digital filter  65  (DF2), where only the mid-to-low frequency signals, i.e., those having a frequency less than f H , are selected for further processing by Processor  66 . These mid-to-low frequency signals are processed by the Processor  66  and converted to appropriate output signals. These output signals are functionally directed to a speaker (e.g., speaker  19  shown in  FIG. 3A ) over signal line  68 . 
     Advantageously, all of the circuits A/D1, A/D2, DF1, DF2, and Processor  66  may be largely digital circuits, and the processing performed thereby may be carried out using programmable digital signal processing (DSP) techniques as are generally known in the art. More significantly, all or most of these circuits may be implemented on the same DSP chip  68 , thus making the overall size of the DSP circuits very small. 
     Moreover, because DSP circuit operation allows, e.g., the cut-off frequencies associated with the DF1 and DF2 digital filters to be precisely set, a sharp separation between the frequencies processed by the first processing channel, comprising MIC1, Pre-Amp1, A/D1, DF1 and a portion of Processor  66 , and the second processing channel, comprising MIC2, Pre-Amp2, A/D2, DF2 and a portion of Processor  66 , to be defined and maintained. Where this sharp separation occurs will vary from user to user, but will typically be in the 500-2000 Hz range. That is, for some users, any frequencies below a first frequency F1, where F1 may be 500 to 2000 Hz, will be considered as a mid-to-low frequency signal that is processed by the second processing channel; whereas any frequencies above this frequency F1 will be considered a high frequency signal that is processed by the first processing channel. 
     In some embodiments, it may be advantageous to overlap the frequency cut-off point between where mid-to-low frequency signals end, and the high frequency signals begin. This overlap amount, if used, will generally only be used in one channel, e.g., the CI channel (the first processing channel shown in  FIG. 3B ), in order to prevent undesirable feedback in the acoustic processing channel (the second processing channel shown in  FIG. 3B ). That is, for some patients, the CI processing channel, which starts with MIC1, may process all frequency signals (or a large subset of the available frequency signals) present within the incoming sound signal  12  that is sensed by MIC1, and use the information content of these frequency signals to help define the electrical stimuli to be applied to the electrode contacts  54  located at or near the distal end of the electrode  52  inserted into the user&#39;s cochlea (as described, e.g., in connection with  FIG. 2 ). However, the acoustic processing channel, which starts with MIC2, will process only those signals within the incoming sound signal  12  that are less than some cut-off frequency F1. The key is that MIC2 be located at a location that is acoustically remote, e.g., on the headpiece  43 , from the SPKR  19  (see, e.g.,  FIGS. 2 ,  3 A and  3 C) from which the mid-to-low frequency signals processed by the second processing channel are broadcast. 
     Next, with reference to  FIG. 3C , a functional schematic diagram of the ear as in  FIGS. 1 and 2  is illustrated that further shows one embodiment of an EAS system wherein two microphones are employed. In many respects, the embodiment shown in  FIG. 3C  is similar to the configuration shown in  FIG. 2 . However, there are critical differences. Foremost in these differences is the location of the microphone used with the hearing aid portion of the EAS system. In  FIG. 2 , the microphone  17  is located at a proximal end of the in-the-ear hearing aid  15 . This location disadvantageously makes the hearing aid very susceptible to feedback. In  FIG. 3C , a microphone  41  used with the hearing aid portion of the EAS system is located at a distance that is acoustically remote from the ear canal  16  or the speaker  19 . As shown in  FIG. 3C , the microphone  41  is located on or near the headpiece  43  of the ICS portion of the system. Such location is acoustically remote from the ear canal  16  or speaker  19  because the amplified sounds  13  emanating from the speaker (SPKR)  19  cannot be readily perceived at this location. Hence, because of this, no or minimal feedback will occur, and in general, the gain associated with the hearing aid amplifier (which may be located inside the BTE speech processor  42  or within the in-the-canal hearing mold casing  15 ′) can be turned up as loud as necessary. 
     In one preferred embodiment, the in-the-canal hearing mold  15 ′ shown in  FIG. 3C  need not be anything more than an ear bud which holds the SPKR  19 . In accordance with this embodiment, the amplifier and power circuits and batteries associated with the hearing aid function can be housed in the BTE speech processor  42 . 
     The SPKR  19  is coupled to its amplification and driving circuits via a coupling link  45 . In its simplest form, this link  45  may be a pair of wires, conveniently arranged in a single cable, as is commonly done with conventional ear buds connected to audio sources, such as an iPod or cell phone. More sophisticated coupling may occur through other means, such as wireless coupling, as is known in the art. When wireless coupling is used, then at least some amplification circuitry, along with wireless reception circuitry and a power source are housed within the ear canal mold  15 ′ along with the SPKR  19 . 
     Alternatively, the link  45  may be an acoustic link provided, e.g., through an acoustic tube that carries the sound wave signals to the ear drum  18 , as is commonly done with many types of hearing aids. In such instance, all of the processing circuits needed to amplify the sound signal are housed, e.g., within the BTE sound processor  42 . The acoustic tube may enter the ear canal from the outside, as is conventionally done with most hearing aids, or it can be inserted deep into the ear canal through an auxiliary tunnel, as described, e.g., in U.S. Pat. No. 6,786,860, incorporated herein by reference. 
     The embodiment shown in  FIG. 3C  senses acoustic sound waves  12  through either microphone  40 , located near the opening of the ear canal  16 , or through microphone  41 , located at an acoustically remote distance from the ear canal  16 . Microphone  40  may be located at the end of a boom  53  connected to an ear hook used with the BTE speech processor  42 . See, e.g., U.S. Pat. Nos. 7,106,873 and 7,167,572, incorporated herein by reference. 
       FIG. 4A  shows a functional block diagram of one preferred embodiment of the EAS system described herein.  FIG. 4A  is very similar to  FIG. 3C , except that the physiological components of the ear are shown in a more schematic fashion in  FIG. 4A  than in  FIG. 3C . Also,  FIG. 4A  illustrates that the microphone  41  used with the hearing aid portion of the EAS system may be located at any location that is acoustically remote from the ear canal  16 , not just at a location that is on or near the headpiece  43 . That is,  FIG. 4A  depicts a microphone  41 ′ that may be positioned in any suitable location. Microphone  41  shown in  FIG. 3C , in contrast, is shown connected to the headpiece  34 , and from there it is coupled through cable  47  to an external housing  49 . The external housing  49  may be a BTE housing, or a body-worn housing. The circuitry associated with both the hearing aid amplifier  15 ″ (of the hearing aid portion of the EAS system) and the speech processor  42  (of the ICS portion of the EAS system) may be housed within the housing  49 . The output of the amplifier  15 ″ is coupled to the SPKR  19  located in the ear canal  16  by a suitable link  45 . As described previously, the link  45  may be of numerous kinds, e.g., wires, wireless, or acoustic. (If an acoustic link is used, the SPKR  19  would actually be located in the housing  49 , not in the ear canal  16  as shown in the drawing, and the amplified sound waves  13  would emanate from an acoustic tube, not shown in  FIG. 4A , coupled at one end to the SPKR  19 , with the other end of the acoustic tube being positioned at a location in or near the ear canal  16  so as to be close to the ear drum  18 .) 
       FIG. 4B  shows a functional block diagram of another preferred embodiment of the EAS system. In most respects,  FIG. 4B  is the same as  FIG. 4A , and the description provided above with respect to  FIG. 4A  applies equally to  FIG. 4B . However, the one main difference between  FIG. 4B  and  FIG. 4A  is location of the SPKR  19 . In  FIG. 4B , the SPKR  19  is placed much closer to the ear drum  18 . The link  45  that couples the SPKR  19  to the AMP  15 ″ may again be of numerous kinds, e.g., wires, wireless, or acoustic. If wires are used, the wires may pass through the ear canal, or they may pass through a tunnel made in the soft tissue behind the auricle  14 . Placing the SPKR  19  deep into the ear canal  16 , as shown in  FIG. 4B , serves to further acoustically separate the SPKR  19  from MIC2 ( 41 ) or MIC3 ( 41 ′), thus preventing feedback. 
     As described above, it is thus seen that an EAS system is provided that includes both a hearing aid adapted to sense and amplify low frequency acoustic sound signals and a cochlear implant adapted to sense high frequency acoustic sound signals. The hearing aid portion of the EAS system has a first microphone  41  or  41 ′ adapted to sense low frequency acoustic sound signals, amplify these sensed low frequency acoustic sound signals, and present the resulting amplified low frequency acoustic sound signals  13  in the ear canal of a user, thereby enabling the user to better hear these amplified sounds using his or her normal hearing processes. The cochlear implant portion of the EAS system includes a second microphone  40  adapted to sense the acoustic sound signals and selectively stimulate the inner ear with electrical stimulation that will be perceived primarily as high frequency acoustic sound signals. Both the cochlear implant portion and the hearing aid portion of the EAS system are coupled to operate on the same ear of the user. 
     As further described herein, it is seen that feedback associated within the hearing aid portion of the EAS system is eliminated by positioning the microphone  41  or  41 ′ at a location that is acoustically remote from the ear canal  16  where the amplified low frequency acoustic sound signals are presented. In contrast, high frequency acoustic sound signals are better sensed through the cochlear implant portion of the EAS system by placing the microphone  40  at a location in or near the ear canal  16 . 
     While the invention herein disclosed has been described by means of specific embodiments and applications thereof, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims.