Patent Publication Number: US-8538055-B2

Title: Semi-permanent canal hearing device and insertion method

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 11/115,907, filed Apr. 26, 2005, titled “Semi-Permanent Canal Hearing Device” which is a continuation of U.S. patent application Ser. No. 09/199,669, filed Nov. 25, 1998, titled “Semi-Permanent Canal Hearing Device” (now U.S. Pat. No. 6,940,988), both of which are fully incorporated herein by reference. 
     This application is related to U.S. patent applications: Ser. No. 09/181,533, filed Oct. 28, 1998, titled “Remote Magnetic Activation of Hearing Devices” (referred to herein as the &#39;533 application”); and Ser. No. 09/190,764, filed Nov. 12, 1998, titled “Battery Enclosure for Canal Hearing Devices” (referred to herein as the &#39;764 application”), now U.S. Pat. No. 6,208,741, all of which are fully incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     a. Technical Field 
     The present invention relates to hearing devices, and, more particularly, to hearing devices that are semi-permanently positioned in the ear canal for improved energy efficiency, sound fidelity, and inconspicuous wear. 
     b. Description of the Prior Art 
     (1) Brief Description of Ear Canal Anatomy and Physiology 
     The external acoustic meatus (ear canal) is generally narrow and tortuous as shown in the coronal view in  FIG. 1 . The ear canal  10  is approximately 23-29 millimeters (mm) long from the canal aperture  17  to the tympanic membrane  18  (eardrum). The lateral-part, a cartilaginous region  11 , is relatively soft due to the underlying cartilaginous tissue. The cartilaginous region  11  of the ear canal  10  deforms and moves in response to the mandibular (jaw) motions, which occur during talking, yawning, eating, etc. Hair  12  is primarily present in the cartilaginous region. The medial part, a bony region  13  proximal to the tympanic membrane, is rigid due to the underlying bony tissue. The skin  14  in the bony region  13  is thin (relative to the skin  16  in the cartilaginous region) and is sensitive to touch or pressure. A characteristic bend  15  roughly occurring at the bony-cartilaginous junction  19  separates the cartilaginous and bony regions  11  and  13 , respectively. The magnitude of this bend varies significantly among individuals. 
     A cross-sectional view of the typical ear canal  10  ( FIG. 2 ) reveals generally an oval shape with a long diameter DL in the vertical axis and a short diameter DS in the horizontal axis. Canal dimensions vary significantly among individuals as shown below in the section titled Experiment-A. The long/short ratio (DL/DS) ranges from 1:1 to 2:1. The diameter ranges from as little as 4 mm (DS in the bony region  13  in small canals) to as much as 12 mm (DL in the cartilaginous region  11  in large canals). 
     Physiological debris  4  in the ear canal is primarily produced in the cartilaginous region  11 , and includes cerumen (earwax), sweat, and oils produced by the various glands underneath the skin in the lateral portion of the cartilaginous region. Cerumen is naturally extruded from the ear canal by the process of lateral epithelial cell migration (see, e.g., Ballachanda, The Human Ear Canal, Singular Publishing, 1950, pp. 195). There is no cerumen production or hair  12  in the bony part of the ear canal. The ear canal  10  terminates medially with the tympanic membrane  18 . Externally and lateral to the ear canal are the concha cavity  2  and the auricle  3 . 
     Several types of hearing losses affect millions of individuals. Hearing loss naturally occurs beginning at higher frequencies (4000 Hz and above) and increasingly spreads to lower frequencies with age. 
     (2) The Limitations of Conventional Canal Hearing Devices 
     Conventional hearing devices that fit in the ear of individuals generally fall into one of 4 categories as classified by the hearing aid industry: (1) the Behind-The-Ear (BTE) type which, as the designation indicates, is worn behind the ear and is attached to an ear mold which fit mostly in the concha; (2) the In-The-Ear (ITE) type which fits largely in the auricle and concha areas, extending minimally into the ear canal; (3) the In-The-canal (ITC) type which fits largely in the concha area and extends into the ear canal (see, e.g., Valente M., Strategies for Selecting and Verging Hearing Aid Fittings, Theme Medical Publishing. pp. 255-256, 1994), and (4) the Completely-In-the-Canal (CIC) type which fits completely within the ear canal past the aperture (see, e.g., Chasin, M. CIC Handbook, Singular Publishing, 1997 (referred to hereinafter as “Chasin”), p. 5). 
     The continuous trend for the miniaturization of hearing aids is fueled by the demand for invisible hearing products in order to alleviate the social stigma associating hearing loss with aging and disability. In addition to the cosmetic advantage of a CIC device  20  ( FIG. 3 ), there are actual acoustic benefits resulting from the deep placement of the device within the ear canal. These benefits include improved high frequency response, less distortion, reduction of feedback and improved telephone use (e.g., Chasin, pp. 10-11). 
     However, even with these significant advances leading to the advent of CIC technology, there remain a number of fundamental limitations associated with the underlying design and configurations of conventional CIC technology. They include: (a) frequent device handling, (b) acoustic feedback, (c) custom manufacturing &amp; impression taking, (d) limited energy efficiency, (e) size limitation due to space inefficiency of enclosure, and (f) occlusion related problems. These limitations are discussed in more detail below. 
     (a) Frequent Device Handling 
     Conventional CIC devices require frequent insertion and removal from the ear canal. Manufacturers often recommend daily removal for cleaning and maintenance of the CIC device (see, e.g., Users&#39;s Instructions, SENSO CIC and Mini Canal, Widex Hearing Aid Co. Feb. 97, pp. 11, 16; and General Information for Hearing aid Users, Siemens Hearing Instruments, Inc. Mar. 98, p. 8). Frequent removal of conventional CICs is also required for relieving the ear from the pressures of the device occluding the cartilaginous region. Furthermore, CIC hearing aid removal is also required in order to replace its battery, typically lasting from 1 to 2 weeks. The manual dexterity required to handle a CIC hearing device frequently poses a serious challenge to the many hearing impaired persons represented by the elderly. These individuals typically suffer from arthritis, tremors, or other neurologic problems that limit their ability to handle a miniature hearing aid. 
     (b) Acoustic Feedback 
     Acoustic feedback occurs when a portion of the sound output, typically from a receiver (speaker), leaks to the input of a sound system such as a microphone of a hearing aid. This leakage often causes a sustained oscillation, which is manifested by “whistling” or “squealing”. Feedback is not only annoying to hearing aid users but also interferes with their communication. Feedback is typically alleviated by occluding (sealing) the ear canal tightly, particularly at the cartilaginous region  11 , as illustrated with the CIC hearing device in  FIG. 3 . 
     (c) Custom Manufacturing &amp; Impression Taking 
     Conventional CIC devices are custom made according to an impression taken from the ear of the individual. The device housing  22  ( FIG. 3 ), known as a shell, is custom fabricated according to the impression, to accurately assume the shape of the individual ear canal. Customizing a conventional CIC is required in order to minimize feedback and to improve comfort of wear. But custom manufacturing is time consuming and results in considerable cost overhead for the manufacturer, ultimately reflected in the price of the CIC device to the consumer (user). Furthermore, impression taking is often uncomfortable for the user. 
     (d) Limited Energy Efficiency 
     The efficiency of a hearing device is generally inversely proportional to the distance or residual volume  25  ( FIG. 3 ) between the receiver (speaker) end  23  and the tympanic membrane  18 ; the closer the receiver is to the tympanic membrane, the less air mass there is to vibrate, and thus, less energy is required. However, due to concerns related to discomfort and difficulty of insertion, CIC products are typically tapered at their medial end  23  (e.g., Chasm, pp. 9-10) and relatively shallow in their placement in order to avoid substantial contact with the bony portion of the ear canal as shown in  FIG. 3 . 
     (e) Size Limitation Due to Space Inefficiency of Enclosure 
     Since a conventional CIC is frequently handled by a wearer, the enclosure  22  ( FIG. 3 ) must be made durably thick in order to protect the components contained within (battery  26 , microphone  27 , amplifier  28  and receiver  29 ). Therefore, a shell, or main housing, is typically made of rigid material such as plastic (e.g. acrylic). Typical thickness for this housing or enclosure of CIC devices is 0.5 to 0.7 mm, which adds considerable dimensions to the conventional CIC. Furthermore, conventional shells enclose the battery along with other components, which makes the overall housing large. This space inefficiency renders the device unsuitable for many individuals with small or highly contoured ear canals who would not be able to comfortably tolerate insertion and wear of a CIC device deep in the ear canal. 
     (f) Occlusion Related Problems 
     (i) Discomfort, irritation and even pain may occur due to canal abrasion caused by frequent insertion and removal of a CIC hearing aid. A removal strand  24  ( FIG. 3 ) is generally provided with CIC devices to assist the wearer in the daily removal process. Due to the resultant discomfort and abrasion, hearing devices are frequently returned to the manufacture for improvement of the custom fit and comfort (e.g., Chasin, p. 44). “The long term effects of the hearing aid are generally known, and consist of atrophy of the skin and a gradual remodeling of the bony canal. Chronic pressure on the skin lining the ear canal causes a thinning of this layer, possibly with some loss of skin appendages” (Chasin, p. 58). 
     (ii) Moisture produced in the cartilaginous ear canal causes damage to the ear canal and the hearing device therein. “The humidity in the occluded portion of the canal increases rapidly. This is worse during hot and humid weather, following exercise” (Chasin, pp. 57-58). It is often recommended that the CIC device should be removed from the ear canal daily to reduce the damaging effects of moisture in the canal. 
     (iii) Cerumen impaction (blockage of the ear canal by earwax) may occur when cerumen, produced in the cartilaginous region, is pushed and accumulated deeper in the bony region of ear canal by the frequent insertion of a CIC hearing device (e.g., Chasin, p. 27, pp. 56-57). Cerumen can also build up on the receiver of the hearing device causing frequent malfunction. Cerumen contamination due to frequent insertion is probably the most common factor leading to hearing aid damage and repair (see, e.g., Oliveira, et al, The Wax Problem: Two New Approaches, The Hearing Journal, Vol. 46, No. 8). 
     (iv) The occlusion effect, a common acoustic problem attributable to occlusion of the ear canal by the hearing device, is manifested by the perception of the user&#39;s (wearer&#39;s) own voice (“self-voice”) being loud and unnatural compared to that with an open (unoccluded) ear canal. This phenomenon is sometimes referred to as the “barrel effect”, since it resembles the experience of talking into a barrel. The occlusion effect, which may be experienced by plugging the ears with fingers while talking, is generally related to self-voice resonating within the ear canal. For hearing aid users, the occlusion effect is inversely proportional to the residual volume  25  ( FIG. 3 ) of air between the occluding hearing device and the tympanic membrane. Therefore, the occlusion effect is considerably alleviated by deeper placement of the device in the ear canal. Incorporating a vent  21  across the CIC hearing device  20  can also alleviate this effect. 
     The above limitations in conventional CIC devices are highly interrelated. For example, when a CIC is worn in the ear canal, movements in the cartilaginous region “can lead to slit leaks that lead to feedback, discomfort, the occlusion effect, and pushing of the aid from the ear” (Chasin, pp. 12-14). The relationship between the limitations is often adverse. For example, occluding the ear canal tightly is desired on one hand to prevent feedback. On the other hand, however, tight occlusion leads to various adverse side effects as mentioned above. Attempts to alleviate the occlusion effect by a vent  21  provide an opportunistic pathway for leakage and feedback. For this reason, the vent  21  diameter is typically limited in CIC devices to 0.6-0.8 mm (e.g., Chasin, pp. 27-28). 
     (3) Review of State-of the-Art in Related Hearing Device Technology 
     Ahlberg et al and Oliviera et al in U.S. Pat. Nos. 4,880,076 and 5,002,151 respectively, disclose a compressible polymeric foam assembly attached to an earpiece of a hearing device. The compressible foam assembly (FIG. 1 of both Ahlberg and Oliviera) is inserted in to the ear canal to couple sound and seal acoustically therein. The foam seal is attached serially to the earpiece, which adds a considerable dimension to overall length of the hearing device. Therefore, the application of such compressible foam assembly is limited to BTE and ITE devices which have housings positioned external to the ear canal. 
     Cirillo in U.S. Pat. No. 4,830,139 discloses means for holding a speaker mold (16 in Cirillo&#39;s FIG. 1) in the ear canal via a sealant made of flexible gelatinous water-soluble material. The mold is attached to a wire ( 18 ) extending to the outside of the ear canal, and therefore, Cirillo&#39;s proposal is presumably also for hearing devices that are positioned outside the ear canal. It does not deal with devices that are completely positioned in the ear canal. Furthermore, since the sealant is water-soluble, it can also be assumed to be suitable only for short-term use as it will deteriorate with moisture exposure (e.g., as will occur when the wearer is taking a shower or is caught in the rain). 
     Sauer et al in U.S. Pat. No. 5,654,530 disclose an insert associated with an ITE device (Sauer&#39;s FIG. 1) or a BTE device (Sauer&#39;s FIG. 2). The insert is stated to be a “sealing and mounting element” made of “soft elastic material having slotted outer circumference divided into a plurality of fan-like circumferential segments”. The sealing element is positioned at the lateral portion of the ear canal as shown in Sauer&#39;s figures. According to the patent, the insert is for ITEs and BTEs only, not for inconspicuous hearing devices that are deeply and completely inserted in the ear canal. The insert as disclosed is used in the cartilaginous area, thus occluding the ear canal in the region of hair, cerumen and sweat production. Clearly, long term use (without daily removal) will interfere in the natural production of physiologic debris. 
     Garcia et al. in U.S. Pat. No. 5,742,692 disclose a hearing device (10 in Garcia&#39;s FIG. 1) attached to a flexible seal  30  which is fitted in the bony region of the ear canal. The device  10  comprises hearing aid components (i.e., microphone  12 , receiver  15  and battery  16 , etc., as shown by Garcia) which are contained within a single “unitary” housing  20 . The device  10  is not likely to fit deeply and comfortably in many small and contoured canals due to the space inefficiency associated with the unitary housing  20 . In addition to the size disadvantage, the device  10  occludes the ear canal in the cartilaginous region as shown in Garcia&#39;s FIG. 2. 
     Henneberger and Biermans in U.S. Pat. Nos. 4,680,799 and 4,937,876, respectively, also disclose hearing aids with conventional housings, which occlude the ear canal and comprise a unitary enclosure for microphone, battery and receiver components therein. 
     Weiss et al. in U.S. Pat. Nos. 3,783,201 and 3,865,998 disclose an alternate hearing device configuration which fits partially in the ear canal (FIG. 1 in both the Weiss &#39;201 and &#39;998 patents) with a separate microphone  14  and receiver  18 . The main housing, enclosing battery and amplifier, is designed to fit in the concha area outside the ear canal as shown. The microphone  14  is positioned in the pima completely outside the ear canal. The device is clearly visible to the casual observer. 
     Geib in U.S. Pat. No. 3,527,901 discloses a hearing device with housing made of soft resilient material, which encloses the entire body of the device. This approach eliminates conventional rigid enclosures, and is presumably more comfortable to wear. However, the unitary flexible enclosure provides no improvement in space efficiency and also poses serious concerns regarding the reliability of interconnects, and of the device in general, during frequent handling. The disclosed hearing device was not designed to fit entirely in the ear canal, Geib stating that “the hearing aid makes a much better fit within the concha and ear canal of the user thereby providing a more effective seal and reducing the problems of direct acoustic feedback” (col 2, lines 40-43). 
     Hardt in U.S. Pat. No. 4,607,720 discloses a hearing device which is mass-producible with a soft sealing plug that is serially attached to the receiver. Although the problem of custom manufacturing is addressed, the unitary enclosure (containing major hearing aid components; battery, microphone and receiver) is, as with other prior art proposals, space-inefficient for deep canal fittings. 
     Voroba et al in U.S. Pat. No. 4,870,688 also disclose a mass-producible hearing aid, which includes a solid shell core (20 in Veroba&#39;s FIGS. 1 and 2) with a flexible covering  30  affixed to its exterior. Similarly, the rigid core represents a unitary enclosure for all major hearing aid components, and thus, is space-inefficient for deep canal fittings. 
     Hartl et al. in U.S. Pat. No. 4,639,556 disclose a hearing aid with a flexible printed circuit board attached to a face-plate. The flexible circuit board and major hearing aid components are also enclosed in a unitary housing (1 in Hartl&#39;s FIG. 1). Similarly, this leads to a space-inefficient design for deep canal fittings. 
     McCarrel et al, Martin, Geib et al, and Adelman, in U.S. Pat. No. 3,061,689, U.S. Pat. No. RE 26,258, U.S. Pat. Nos. 3,414,685 and 5,390,254, respectively, disclose miniature hearing devices with a receiver portion flexibly separate from a main part. The receiver portion insertable into the ear canal with the main part occupying the concha (McCarrel&#39;s FIG. 2, Geib&#39;s FIG. 10, and Adelman&#39;s FIG. 3B). This placement facilitates access to the device for insertion and removal. In each of these disclosures, the aforementioned main part contains all the major components of the hearing device, including among others the battery, amplifier and microphone, except the receiver. Therefore, this main part is not sufficiently space-efficient to fit past the aperture of the ear canal for most individuals. 
     Shennib et al in U.S. Pat. No. 5,701,348 disclose an articulated hearing device with flexibly connecting modules, stating that “the main module  12  includes all of the typical components found in hearing devices, except for the receiver” (col. 6, lines 64-66). The main module includes a battery  16 , a battery compartment  15 , circuit  17  (amplifier) and microphone  14 . Because if its articulated design and assorted soft acoustic seal  43 , the hearing device disclosed by Shennib is suitable to fit a variety of ear canals without resorting to custom manufacturing, and thus can be mass-producible as disclosed. Although a CIC configuration is disclosed (see Shennib&#39;s FIG. 23), the depth of insertion, particularly for small and contoured ear canals, is severely limited by the design of the main module  12  which contains the power source (battery) along with other major components (e.g., the microphone). Furthermore, in each of its disclosed configurations, the device substantially occludes the ear canal in the cartilaginous region, which would interfere with hair and the natural production of physiologic debris. In addition, the disclosed CIC configuration is designed for insertion and removal by a wearer with good dexterity (col. 11, lines 18-20). Therefore, the disclosed CIC device would be unsuitable for continuous long-term use in the ear canal, particularly for persons lacking such dexterity. 
     It is the principal objective of the present invention to provide a highly space-efficient hearing device, which is suitable to be completely positioned in the ear canal. 
     Another objective is to provide a design for a hearing device which is mass-producible, and which requires neither custom manufacture nor the taking of individual ear canal impressions. 
     A further objective of the invention is to provide a hearing device which occludingly seals the ear canal in the bony region, but not at the cartilaginous region, and thus does not interfere with hair and the natural production and elimination of physiologic debris in the ear canal. 
     Yet another objective is to provide a semi-permanent hearing device which is inserted by a physician, or by other professionals under the supervision of a physician, for long-term use in the ear canal. 
     Semi-permanent, or alternatively long-term use, is defined herein as continuous placement and use of the hearing device within the ear canal without any removal, daily or otherwise, for at least a month. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention provides a semi-permanent hearing device which is completely positioned within the ear canal of an individual for long-term use. The device comprises a sealing retainer substantially positioned in the bony region of the ear canal and a core assembly comprising a receiver assembly coaxially positioned within the sealing retainer. 
     The core assembly extends from the sealing retainer to the cartilaginous region in a non-occluding fashion, thus minimizing interference with hair and earwax production present in the cartilaginous part of the ear canal. In a preferred embodiment of the invention, the core assembly includes a battery assembly including a battery and a thin enclosure having substantially the shape and dimensions of the battery which is encapsulated therein. A connector having the shape of thin ribbon film provides electrical and flexible mechanical connectivity between the receiver assembly, centrally positioned battery assembly, and microphone assembly positioned in the cartilaginous region. The invention is characterized by the absence of a unitary enclosure or main housing which typically encloses the battery and other components in prior art hearing device designs. 
     In the preferred embodiment, the hearing device is mass-producible and accommodates a variety of canal shapes and sizes without need for custom manufacturing or canal impressions. This desirable objective is accomplished by virtue of the flexibility of the universal core assembly and conformity of the assorted sealing retainer. 
     The hearing device of the invention is preferably inserted by a physician, or by another professional under the supervision of a physician, for placement entirely within the ear canal and exceptionally close to the eardrum. The space and energy efficient design allows for a comfortable continuous use within the ear canal for extended periods of time, exceeding one month, without the requirement of daily removal as with conventional CICs. In the preferred embodiments, the device is remotely switched on/off by a remote control for optionally conserving the battery energy while the device remains in the ear canal during sleep or non-use. 
     The invention eliminates the need for manual insertion and removal by the wearer and is therefore particularly suited for hearing impaired persons of poor manual dexterity. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and still further objectives, features, aspects and attendant advantages of the present invention will become apparent from the following detailed description of certain preferred and alternate embodiments and method of manufacture and use thereof constituting the best mode presently contemplated of practicing the invention, when taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a side view of the external ear canal, described above; 
         FIG. 2  is a cross-sectional view of the ear canal at the bony-cartilaginous junction for (a) small canal, (b) average size canal and (c) large canal, showing the relative dimensions of standard button cell hearing aid batteries, sizes 10A and  312 ; 
         FIG. 3  is a side view of the ear canal occluded by a conventional CIC hearing aid positioned therein, described above; 
         FIG. 4  is a side view of the ear canal showing an embodiment of the semi-permanent canal device of the present invention positioned completely therein, in which the cartilaginous region is unoccluded and the bony region is occluded with a sealing retainer; 
         FIG. 5  is a detailed side view of the semi-permanent canal device of  FIG. 4 , further illustrating replaceable debris guards for the microphone and receiver; 
         FIGS. 6   a  and  6   b  are cross-sectional views of the ear canal showing the non-occlusive microphone assembly of an embodiment of the canal device of the present invention positioned in the cartilaginous region, providing substantial air-space and no contact with the walls of the ear canal ( FIG. 6   a ), and substantial air-space and minimal contact with the walls or physiologic debris of the ear canal ( FIG. 6   b ); 
         FIGS. 7   a  and  7   b  are cross-sectional views of the ear canal showing the receiver assembly and sealing retainer of an embodiment of the canal device of the invention positioned in the bony region with occlusion thereof ( FIG. 7   a ), and with venting incorporated in the sealing retainer ( FIG. 7   b ); 
         FIG. 8  is an electrical schematic diagram of a prototype embodiment of the canal device of the invention; 
         FIG. 9  is a graph of the acoustic response of the prototype embodiment of  FIG. 8  showing the acoustic effect with and without the moisture-proof debris guards placed on the microphone and the receiver of the prototype embodiment; 
         FIG. 10  is a detailed exploded side view of the flexible connector, battery, microphone and receiver parts of an embodiment of the canal device of the present invention, showing the parts unassembled; 
         FIG. 11  is a cross-sectional view of the ear canal showing the battery assembly of an embodiment of the canal device of the invention positioned therein, with flexible connector, battery and battery enclosure; 
         FIG. 12  is a side view of the ear canal showing a programmable embodiment of the canal device of the invention positioned in the ear canal with sealing retainer extending substantially over the battery, and also illustrating a probe tube system with probe tube and external amplifier according to the invention; 
         FIG. 13  is a side view of the ear canal showing an embodiment of the canal device of the invention positioned in the ear canal with a latchable magnetic switch and an external control magnet; 
         FIG. 14   a  is a detailed view of a moisture-proof debris guard in the form of an adhesive pad showing the adhesive layer and receiver sound port for an embodiment of the canal device of the invention; and  FIG. 14   b  is a perspective view of the moisture-proof adhesive pad of  FIG. 14   a  showing the adhesive layer and adhesive-free area; 
         FIG. 15  is a side view of the ear canal showing an alternate embodiment of the canal device of the invention positioned entirely in the ear canal and substantially in the bony region thereof; 
         FIGS. 16   a  and  16   b  are perspective views of a preferred embodiment of the sealing retainer of the canal device, taken respectively from the side ( FIG. 16   a ) and from the lateral end ( FIG. 16   b ), showing a lateral cavity which partially accommodates the battery assembly indicated by the dotted circle; and 
         FIG. 17  is a side view of the ear canal showing the central location of the three regions representing the cartilaginous region (C), the bony-cartilaginous junction region (J) and the bony region (B). 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention provides a semi-permanent hearing device which is adapted to be entirely positioned in the ear canal for long term use. For the sake of additional clarity and understanding in the ensuing detailed description, the disclosures of the aforementioned related co-pending &#39;533 application and &#39;764 application (see section titled “Cross-Reference to Related Applications”, above) are incorporated herein by reference. 
     The canal hearing device  30  of the invention will be described with reference to  FIGS. 4-16 , in which the same reference numbers are used throughout to indicate elements which are common to the several Figures. Hearing device  30  generally comprises a core assembly  35  and a sealing retainer  70  constructed and adapted to be positioned substantially in the bony region  13  of the ear canal. The core assembly  35  includes a receiver (speaker) assembly  60 , which is coaxially positioned within the sealing retainer  70 . 
     The core assembly  35  extends to the cartilaginous region  11  in a non-occluding fashion, thus minimizing interference with hair and earwax production present in the cartilaginous part of the ear canal  10 . The core assembly  35  also includes a battery assembly  50  having a shape and dimensions substantially equivalent to those of the enclosed battery  51 , recognizing that battery assembly  50  has a slightly larger size to accommodate snug enclosure of the battery  51  therein. A connector  53 , in the shape of thin circuit film or ribbon cable, provides electrical and mechanical connectivity between the receiver assembly  60 , the battery assembly  50 , and a microphone assembly  40 , the latter being positioned in the cartilaginous region  11  when the hearing device is fully inserted and seated in the ear canal for normal use. The connector  53  is enclosed within the thin enclosure  52  of the battery assembly  50  and extends to the microphone assembly  40  and receiver assembly  60  for connection thereto. 
     In a preferred embodiment, shown in  FIGS. 4-7 , the sealing retainer  70  is adapted to be positioned, as shown, substantially in the bony region  13  concentrically or coaxially over the receiver assembly  60 . The sealing retainer  70  is configured to provide the primary support for the device  30  within the ear canal  10 . To that end, sealing retainer  70  substantially conforms to the shape of walls  14  of the ear canal in the bony region  13  and retains the device securely within the ear canal  10 . The microphone assembly  40 , including a microphone  43  therein, is non-occludingly positioned in the cartilaginous region  11  with little or no contact with the walls of the ear canal, thus allowing for a substantial air space  49  therebetween as shown in  FIGS. 4 ,  6   a  and  6   b . This minimal contact of the microphone assembly  40  allows for natural production and lateral migration of cerumen (earwax) and other debris in the cartilaginous region  11 . The receiver assembly  60 , in contrast, occludes the ear canal in the bony region  13  via the associated sealing retainer  70 , as shown in  FIG. 7 . 
     The microphone assembly  40 , battery assembly  50 , and receiver assembly  60  each having an individual thin encapsulation  45  ( FIGS. 6   a ,  6   b ),  52  ( FIG. 11) and 62  ( FIGS. 7   a ,  7   b ), respectively. The encapsulation preferably comprises a moisture-proof material or coating such as silicone, paralene or acrylic. The thin encapsulation may be made soft, such as soft silicone, or rigid, such as hard acrylic. Any exposed part of connector  53  extending from battery assembly  50  must be moisture-proofed in order to protect the hearing device from the damaging affects of moisture produced within or outside the ear canal. 
     The connector  53  and battery  51  are encapsulated by a thin disposable enclosure 52 according to the disclosure of the &#39;764 application. The battery assembly  50  minimally occludes the ear canal and is preferably positioned substantially at or beyond the bony-cartilaginous junction  19  ( FIG. 1 ; see, also, J of  FIG. 17 ). 
     In order to protect the microphone and receiver of the hearing device  30  from the damaging effects of moisture and debris, microphone debris guard  42  ( FIG. 5 ) and receiver debris guard  67  are placed on microphone and receiver ports  46  and  63 , respectively. The microphone guard  42  in the embodiments of  FIGS. 4 and 5  is in the form of a replaceable cap with a cap body  48  ( FIG. 5 ) fitted over the microphone port  46  (in the direction of arrow  31 ) and guard member  47  made of a thin membrane or screen material that is substantially transparent to sound. Similarly, receiver guard  67  ( FIG. 5 ) may also be in the form of a replaceable cap with cap body  65  fitted over the receiver in the direction of arrow  32  with guard member  65  positioned over receiver sound port  63 . The effect of the microphone and receiver guards  42  and  67 , respectively, on the acoustic response of the hearing device is detailed below in the section titled Experiment-C. 
     When the hearing device  30  is fully inserted in its normal position in the ear canal  10 , the microphone assembly  40  is positioned at the cartilaginous region  11  with a substantial air-space  49  all around the microphone assembly ( FIGS. 6   a ,  6   b ), between the enclosure  45  of the microphone assembly and the canal skin  16  (walls). The microphone assembly  40  is positioned substantially clear from hair  12  and physiologic debris  4  produced in the cartilaginous region  11 . 
     The alternate ear canal  10 ′ of  FIG. 6   b  is depicted as being relatively narrow, and although a substantial air-space  49  is also present, the microphone assembly  40  makes minimal contact with the wall of the canal or with physiologic debris  4  therein at the contact area  5 . However, connector  53 , which is flexibly connected to battery assembly  50  in the preferred embodiment, allows microphone assembly  40  freedom to move along the cross-section of the ear canal in response to pressure from physiologic debris  4  production or canal deformations associated with jaw movements. 
     As shown in  FIGS. 7   a  and  7   b , the receiver assembly  60  is positioned in ear canal  10  at bony area  13 , with sealing retainer  70  in direct contact with canal skin  14  (walls), thus occluding the bony area of the canal. A vent  61  ( FIGS. 5 and 7   a ) is provided for pressure equalization during insertion and removal or during changes in atmospheric pressure. The vent may alternatively be provided across the sealing retainer  70  ( FIG. 7   b ). The vent  61  is also provided to minimize occlusion effects described above. 
     The microphone assembly  40  in the preferred embodiment of  FIGS. 4-6 , comprises a microphone  43 , a control element  41  (i.e., volume trimmer as shown in  FIG. 5 ) and switch assembly  44 . The switch assembly  44  comprises a latchable read-switch assembly (RS in  FIG. 8 ), which is remotely activated by a remote magnet (e.g.,  120  in  FIG. 13 ) according to the disclosure in the &#39;533 application. The microphone  43  comprises a microphone transducer with an integrated signal processing amplifier (for example, series FI-33XX manufactured by Knoweles Electronics of Itasca, Ill.). This integration reduces the size of the microphone assembly, which further reduces occlusion effects within the ear canal at the cartilaginous region. Alternatively, the signal processing amplifier may be a separate component, as shown at  28  in the embodiment of  FIG. 12 . 
     A schematic diagram of an electroacoustic circuit of the embodiment in  FIGS. 4-7  is shown in  FIG. 8 . The microphone M, comprising a microphone transducer and signal processing amplifier integrated therein, picks up acoustic signals S.sub.M entering the ear canal and produces amplified electrical signal at terminal OUT of microphone M. The electrical signal is then delivered to input (IN) terminal of the receiver R via coupling capacitors C 1  and C 2 . The receiver R then produces amplified acoustic signal S.sub.R for delivery to the tympanic membrane  18  ( FIG. 4 ). Volume trimmer R.sub.G, connecting the output (OUT) and feedback (Fit) terminals of the microphone M, is adjusted to set the gain (volume) of the electroacoustic circuit. Jumper JI (also shown in  FIG. 5 ) may be removed (by cutting for example) to reduce the coupling capacitance, thus altering the frequency response of the hearing device as known to those skilled in the art of electronics. Other jumpers (not shown) may also be incorporated in order to increase the range of adjustable parameters of the hearing device. A capacitor CR is employed to stabilize the supply voltage (V+) across the supply terminals (+and−) of the receiver R. 
     The acoustic response of a device fabricated according to the embodiment of  FIGS. 4-7  and the electroacoustic circuit of  FIG. 8  was measured and plotted in  FIG. 9  with and without moisture-proof guards as detailed below in the section titled Experiment-C. 
     The connector  53 , in the preferred embodiment shown in more detail in  FIG. 10 , comprises a flexible film  54  with circuit wires  55 ,  56 ,  57  and  58 , which electrically interconnect the microphone  43 , receiver  64 , battery  51 , volume trimmer  41 , and other components (which are not shown, for the sake of clarity), such as switch assembly  44  (shown in  FIG. 5 ) and capacitors. The microphone  43  (shown unassembled) is soldered to the connector  53  via solder terminals  81  on the lateral section  83  of the flexible film  54  and solder terminals  81 ′ on the microphone  43 . Similarly the receiver  64  is soldered to the connector  53  via solder terminals  82  on the medial section  85  of the flexible film  54  and solder terminals  82 ′ on the receiver  64 . Conductive pads  91  and  92  on the connector provide power connectivity from the positive  94  and negative  97  ( FIG. 11 ) terminals, respectively, of the battery  51 . Volume trimmer  41  is also connected to solder terminals  81  via trimmer solder terminals  41 ′. 
     The lateral and medial sections  83  and  85  respectively of film  54  are flexibly bendable with respect to the main section  87 , thus allowing the connected microphone assembly  40  and receiver assembly  60  to articulate within the ear canal during insertion and removal of the hearing device. A crossing section  88  of the connector  53  also bends in the direction of arrow  93  (into the paper) in order to connect conductive pad  92  to the negative terminal  97  ( FIG. 11 ) of the battery. The flexible film  54  is provided with relief notches  84 ,  86  and  89  which increase the flexibility of the sections  83 ,  85  and  88 , respectively. The battery  51 , main section  87 , and crossing section  88 , are encapsulated by thin disposable battery encapsulation  52  ( FIG. 11 ) for securing the connector  53  and the associated conductive pads  91  and  92  to the battery. The main section  87  includes a vent hole  95  for allowing air circulation to battery hole  96 , typically available in air-zinc hearing aid batteries. Similarly, the battery encapsulation  52  must allow for the necessary aeration of the battery enclosed therein. 
       FIG. 11  shows a cross sectional view of the battery assembly  50  in the ear canal  10  showing main section  87  of connector  53 , battery  51  and battery encapsulation  52 . The crossing section  88 , extending from main section  87  is also shown crossing to the negative terminal  97  of the button cell battery  51 . Circuit wires  55 ,  56  and  57  are also shown. The battery encapsulation  52  is thin and substantially conforms to the shape of the battery, thus adding negligible dimensions to the enclosed battery. The battery enclosure should be less than 0.3 mm in thickness in order for the battery assembly to minimally occlude the ear canal and to fit comfortably in the vicinity of the bony-cartilaginous area for most individuals. 
     In another embodiment, shown in  FIG. 12 , the hearing device  100  has a microphone assembly  40 , which extends substantially laterally in the cartilaginous area  11  as shown. The sealing retainer  70 , although remaining substantially in the bony region  13 , is concentrically positioned over both the receiver assembly  60  and the battery assembly  50 . The receiver assembly  60  protrudes from the sealing retainer medially towards the tympanic membrane  18 . The hearing device  100  is also shown as being programmable with a programming receptacle  101  for receiving programming signals from a programming connector  102 . The programming connector comprises programming pins.  103  which are temporarily inserted into the programming receptacle  101  during the programming of the hearing device  100 . The capability to be programmable allows hearing device  100  to be electronically adjusted via an external programming device  105  (P) and its associated programming cable  106 . Other means for remotely programming or adjusting a hearing device are well known in the field of hearing aids and include the use of sound, ultrasound, radio-frequency (RF), infrared (IR) and electromagnetic (EM) signals. 
       FIG. 12  also shows a probe tube system  10  for the measurement of sound pressure level (SPL) produced by the hearing device  100  in the ear canal. The probe tube system comprises a probe tube  111 , a microphone  112  and amplifier (A)  113 . Electrical cable  116  connects the microphone  112  to the amplifier  113 . The probe tube  111  is inserted in the ear canal with its tip  115  past the receiver assembly  60  near the tympanic membrane  18 . Probe tube measurements in the ear canal are employed during the fitting process for the in-situ (while in the ear canal) electroacoustic adjustment and verification of the fitted hearing device. 
     Removal handle  107  may be provided for the removal of the hearing device  100 , particularly during an emergency situation, such as infection of the ear canal or irritation therein. 
     In a preferred embodiment of a remote control, shown in  FIG. 13 , the hearing device  30  comprises a latchable reed-switch assembly  44  (RS) for remotely powering the hearing device ON/OFF via an external control magnet  120  which is positioned by the wearer (user) at the vicinity of the concha  2 . The control magnet  120  in the preferred embodiment has two opposing polarities; a north (N) pole  121  and south (S) pole  122 , across the length of the control magnet  120  as shown. The flux lines  123  emanating from the north pole towards the south pole affect the lateral (nearer) lead  44 ′ of latchable reed-switch assembly  44 . Flux lines  123  either latch on or off the reed-switch assembly  44  according to the polarity of the control magnet  120  nearest to lead  44 ′. The read-switch assembly  44  comprises a latching magnet (not shown) as disclosed in greater detail in the aforementioned &#39;533 application, and allows hearing device  30  to be turned off to conserve battery power during sleep and other non-use periods while the device remains in the ear canal for long-term use. 
     The encapsulations  45  and  62  of the microphone receiver assemblies  40  and  60 , respectively, are each made of thin protective material that substantially conforms to the shape of the components encapsulated therein. The thickness of each encapsulation is preferably less than 0.3 mm in order to minimize occlusion of the microphone assembly  40  (see  FIGS. 6   a  and  6   b ) in the ear canal and to maximize the relative dimension of the conforming sealing retainer  70  in the bony region  13  (see  FIGS. 7   a  and  7   b ). Since the semi-permanent hearing device of the invention is handled relatively infrequently, the thickness of the encapsulation can be safely made substantially thinner than conventional enclosures of CIC devices which are typically in the range of 0.5-0.7 mm. 
     In another embodiment of the moisture-proof debris guard, shown in  FIGS. 14   a  and  14   b  for a receiver assembly  60 , the debris guard  67  is made in the form of an adhesive pad. The receiver debris guard is composed of an acoustically-transparent material  65  with an adhesive layer  69  on its lateral surface for attachment to the medial surface  63 ′ of receiver assembly  60 . The receiver assembly&#39;s medial surface  63 ′ includes the receiver sound port  63  which emits receiver sound SR that passes through the debris guard  67  as illustrated by the arrow. The adhesive layer  69  is partially relieved from adhesive material in the adhesive-free area  65 ′ corresponding to or mating with receiver sound port  63 . The adhesive-free area  65 ′ is necessary since adhesives are generally not acoustically transparent, and thus will adversely alter the frequency response of the receiver  64  if applied directly over the sound port  63 . The adhesive pad configuration of the debris guard is equally applicable for both the microphone and receiver sound ports, as shown at  42  and  67 , respectively, in  FIGS. 12-15 . The adhesive pad is preferably replaceable and disposable. 
     The present invention, shown with button cell batteries in the above embodiments, is equally suited to accommodate other battery shapes and configurations as they are likely to be available in future hearing aid applications. The thin enclosure of the battery assembly of the present invention, regardless of the type of battery used, conforms substantially to the shape of the enclosed battery with encapsulation thickness not to exceed 0.3 mm for the preferred embodiments of the invention. 
     For example, in another embodiment of the present invention, shown in  FIG. 15 , a cylindrical battery  51  is employed with a hearing device  130  substantially positioned in the bony region  13  of the ear canal  10 . The microphone end  132  of the core assembly  35  extends laterally and non-occlusively in the cartilaginous region  11 . The receiver end  133  is coaxially positioned within sealing retainer  70 , which acoustically seals and conforms in the bony region  13 . A thin encapsulation  131 , not exceeding 0.3 mm, protects the entire core assembly  35 , which comprises the microphone  43 , battery  51  and receiver  64  therein. 
     The sealing retainer  70 , shown in greater detail in  FIG. 16 , comprises a soft compressible and conforming material such as polyurethane foam or like material (a polymer) or silicone or like material. The sealing retainer  70  must provide significant acoustic attenuation in order to seal and prevent feedback. In a preferred embodiment of the sealing retainer fabricated and tested within ear canals of individuals, a polyurethane foam sealing retainer was molded from a mixture of 1-part aqueous solution (Polymer component Type IA, manufactured by Hamshire Chemicals, Lexington, Mass.) and 2-part prepolymer (HYPOL™ 2002 also manufactured by Hamshire Chemicals). The mixture was poured into a silicone mold (REDU-IT.™ manufactured by American Dental Supply Co. of Easten, Pa.) and allowed to heat cure at approximately 195.degree. F for about 15 minutes prior to removing from the silicone mold at room temperature. 
     The molded sealing retainer  70  did not include any rigid core material therein in order to maximize the fit and comfort within the bony region of the ear canal. The sealing retainer  70  was made oval with long diameter DL approximately 1.6 times that of the short diameter DS. The inferior (lower) portion  74  is relatively pointed to match the shape of typical ear canals in the bony region. The sealing retainer  70  is substantially hollow with air-space  72  between the body  73  of the sealing retainer and the receiver assembly  60  when inserted therein. The medial opening  71  of the sealing retainer is stretchable and is made smaller than the diameter of the receiver assembly  60  in order to provide a tight fit for sealing and securing the receiver assembly and the associated hearing device within the ear canal. Vertical and horizontal cavities  75  and  76 , respectively, in the shape of a cross, extend medially from the lateral end of the sealing retainer  70 . These cavities, in conjunction with the internal air-space  72 , increase the compressibility and conformity of the sealing retainer so that it can be worn more comfortably in the bony region  13  which is known for being extremely sensitive to pressure. Furthermore, the cavities  75  and  76  allow for partial enclosure of the battery assembly (dotted circle)  50  therein as shown in  FIG. 16   a.    
     The sealing retainer  70 , made of polyurethane foam material for example as described above, is compressible and subsequently expandable with time, thus allowing for a temporary compression state prior to and during insertion into the ear canal and a subsequent expansion to conform to the ear canal and seal therein. 
     In a preferred embodiment according to the invention, the sealing retainer  70  was fabricated in an assortment of four sizes (small, medium, large and extra-large) to accommodate the broadest range of ear canals among the population studied. The dimensions of such fabricated assortment are tabulated in Table 1 below. The dimensions were partially derived from measurements of actual ear canal dimensions obtained from cadaver impressions as explained below in the section titled Experiment-A. The sealing retainer may be produced in an assortment of other sizes and shapes as needed to accommodate an even wider diversity of ear canals when studied. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                 Short Diameter 
                 Large Diameter 
               
               
                   
                 Size 
                 (DL in mm) 
                 (DL in mm) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Small 
                 4.5 
                 7.25 
               
               
                   
                 Medium 
                 5.75 
                 9.35 
               
               
                   
                 Large 
                 7.3 
                 12 
               
               
                   
                 Ex-Large 
                 9.0 
                 15 
               
               
                   
                   
               
            
           
         
       
     
     The sealing retainer is preferably disposable and must be biocompatible and hypoallergenic for a safe prolonged wear in the ear canal. The sealing retainer may incorporate a vent  6  as shown in  FIG. 7   b . This vent may created by inserting or molding a narrow-diameter silicone tube therein, for example. 
     Certain individuals may have difficulty wearing the sealing retainer due to the sensitivity of their ear canal, medical condition, or other concerns. Therefore, the sealing retainer may be separately inserted, without the core assembly, for a period of time sufficient to assess comfort and appropriateness of wear prior to inserting the entire hearing device semi-permanently. This may represent a “trial wear” for an individual who may be reluctant to wear or purchase the device for whatever reason. 
     The semi-permanent hearing device of the present invention comprises a disposable battery, disposable battery enclosure, or alternatively a disposable battery assembly with combined battery and enclosure. However, as energy efficiency improvements in battery, circuit and transducer technologies continue to improve, the preferred embodiment may be that of a disposable core assembly with assorted sealing retainers as described above. 
     EXPERIMENT A 
     In a study performed by the applicants herein, the cross-sectional dimensions of ear canals were measured from 10 canal impressions obtained from adult cadaver ears. The long (vertical) and short (horizontal) diameters, DL and DS respectively, of cross sections at the center of three regions in the ear canal (see  FIGS. 2 and 17 ) were measured and tabulated. These regions represent the cartilaginous (C), the bony-cartilaginous junction (J), and the bony (B) regions. The diameters where measured across the widest points of each cadaver impression at each region. All measurements were taken by a digital caliper (model CD-6″CS manufactured by Mitutoyo). The impression material used was low viscosity Hydrophilic Vinyl Polysiloxane (manufactured by Densply/Caulk) using a dispensing system (model Quixx manufactured by Caulk). Measurements are set forth in Table 2, below. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 2 
               
             
            
               
                   
                   
               
               
                   
                 C-Region 
                 J-Region 
                 B-Region 
               
               
                   
                 Diameters in mm 
                 Diameters in mm 
                 Diameters in mm 
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 Short  
                   
                 Short  
                   
                 Short 
                   
               
               
                 Sample # 
                 (DS) 
                 Long (DL) 
                 (DS) 
                 Long (DL) 
                 (DS) 
                 Long (DL) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 1-R 
                 7.8 
                 10.3 
                 8.1 
                 10.7 
                 8.0 
                 10.5 
               
               
                 1-L 
                 7.8 
                 11.9 
                 8.3 
                 12.2 
                 8.1 
                 11.2 
               
               
                 2-R 
                 3.8 
                 8.9 
                 4.0 
                 8.9 
                 4.2 
                 8.9 
               
               
                 2-L 
                 5.3 
                 8.1 
                 4.4 
                 8.8 
                 4.3 
                 8.6 
               
               
                 3-R 
                 5.5 
                 6.3 
                 4.7 
                 6.7 
                 5.0 
                 7.7 
               
               
                 3-L 
                 4.9 
                 6.5 
                 4.9 
                 6.5 
                 4.9 
                 7.3 
               
               
                 4-R 
                 6.9 
                 9.2 
                 6.5 
                 9.6 
                 6.7 
                 10.4 
               
               
                 5-R 
                 6.9 
                 9.2 
                 7.2 
                 8.4 
                 7.5 
                 9.5 
               
               
                 5-L 
                 6.8 
                 8.2 
                 7.6 
                 9.4 
                 7.5 
                 8.7 
               
               
                 7-L 
                 6.3 
                 7.0 
                 5.1 
                 6.7 
                 4.9 
                 6.7 
               
               
                 Average 
                 6.2 
                 8.6 
                 6.1 
                 8.8 
                 6.1 
                 9.0 
               
               
                   
               
            
           
         
       
     
     Results and Conclusion 
     The diameter dimensions of the ear canal vary significantly among adult individuals. In general, variations occur more so across the short (horizontal) diameters. Furthermore, the ear canal is slightly narrower (long/short ratio) in the bony region than in the other two regions. Although not apparent from the above measurements, the cartilaginous region is expandable which facilitates insertion of wider objects through it towards the deeper region, if necessary. 
     EXPERIMENT B 
     A test of insertion fit of the semi-permanent canal device was performed using the battery assembly of the invention. The battery assembly was selected because it represents the largest of all assemblies in the hearing device according to the present invention. 
     Using the 10 cadaver impressions described above in Experiment-A,  10  actual-size ear canal models were fabricated by dip-fanning clear acrylic material (Audacryl-acrylic manufactured by Esschem). Two battery assemblies according to the embodiment of  FIGS. 10-11  were fabricated and inserted in each of the 10 ear canal models up to the bony-cartilaginous junction area. The first assembly comprised a size-10A battery and the second comprised size-312 battery (each is a standard button cell hearing aid battery; see  FIG. 2 ). Each battery assembly included a thin flexible connector and was encapsulated with silicone conformal coating (model MED 10-6605 manufactured by NuSil). The thickness of the coating measured approximately 0.05 mm, thus adding negligible dimensions to the battery assembly and flexible connector thereof. The diameter (D) and height (H) of each assembly was measured across the widest points as tabulated in Table 3, below. 
       FIG. 2  is a cross-sectional view of the ear canal at the bony-cartilaginous junction for (a) the smallest canal, (b) an average size canal and (c) the largest canal. The relative dimensions of standard 10A and 312 batteries are also shown. 
     The thickness of several shells of conventional hearing devices were also measured for comparison analysis (measuring between 0.5 mm and 0.7 mm). For a conventional hearing device enclosing size-10A battery, the added dimensions of (1) the shell (0.5 mm or more, adding a minimum of 1 mm to the dimensions) and (2) other enclosed components, prohibit insertion of the device at the bony-cartilaginous junction (J) area for at least 5 of the above ear canals (2-R, 2-L, 3-R, 3-L and 7-L). This is further exacerbated by the fact that ear canals are often tortuously contoured, thus making it painful if not impossible to insert the conventional CIC device too deeply in seeking to gain access to the bony region of the ear canal. For conventional CIC devices with size-312 battery (larger than 10-A), deep fitting is only likely for very large ear canals, such as 1-R and 1-L. 
     
       
         
           
               
               
               
             
               
                   
               
               
                 Battery Assembly 
                 Height (H) in mm 
                 Diameter (D) in mm 
               
               
                   
               
             
            
               
                 10A Bat. 
                 4.4 (H) 
                 6.5 (D) 
               
               
                 312 Bat. 
                 4.5 (H) 
                 8.0 (D) 
               
               
                   
               
            
           
         
       
     
     Results and Conclusion 
     The first battery assembly (size-10A) was successfully inserted up to the bony-cartilaginous junction (J) region in 9 of the 10 ear canal models, excepting 2-R which has dimensions of 4.0.times.8.9 mm (D.sub.S.times.D.sub.L) as shown in  FIG. 2 . 
     The second battery assembly (size-312) was successfully inserted up to the bony-cartilaginous junction in 5 of the 10 ear canal models. This is particularly significant, since size-312 batteries are virtually excluded from conventional CIC devices due to their excessive size in conjunction with conventional CIC designs. 
     The results confirm that the present invention is more space-efficient and would allow the battery assembly to fit in the bony-cartilaginous junction area and beyond for most adult individuals with size-10A batteries and a significant percentage of adult individuals with size-312 batteries. 
     EXPERIMENT C 
     A prototype of the semi-permanent hearing device according to the embodiment of  FIGS. 4-10  was fabricated and positioned by an otolaryngologist (ear-nose-throat physician) in the left ear canal of a 55 year old male subject who suffered a moderate level of high frequency hearing loss. 
     The circuit of  FIG. 8  was implemented with a miniature microphone/amplifier (model FI-3342 manufactured by Knowles Electronics of Itasca, Ill.), class-D receiver (model FS3379 also manufactured by Knowles Electronics), and miniature 250K ohm volume trimmer RG (model PI-62 manufactured by Microtronics A/S of Denmark). Miniature capacitors C 1 , C 2  and CR with values of 2.2 nF, 0.01 uF and 2.2 uF, respectively were employed. A reed switch assembly (RS) employing a miniature reed-switch (model HSR-003DT, manufactured by Hermetic Switch, Inc. of Chickasha, Okla.) and a miniature Neudymium Iron Boron (NdFeB) magnet for latching the reed-switch. 
     Two layers of thin Kapton tape (#042198 GUA distributed by Economic Packaging Corp. of Milpitas, Calif.) were employed to fabricate a thin flexible connector which embedded circuit wires made of 44 AWG Litz wire. 
     The microphone assembly, comprising microphone amplifier M, reed-switch assembly RS, volume trimmer RG, and lateral section  83  of flexible connector  53  were glued together using cyanoacrylate (#20269, manufactured by Loctite Corp. of Rocky Hill, Conn.). The microphone assembly was then encapsulated by thin moisture proofing silicone material (E4 I manufactured by Wacker, Werk Burghausen of Germany). The receiver assembly, comprising receiver and CR capacitor was similarly encapsulated by silicone material and was flexibly connected to the Kapton tape connector. 
     The moisture-proof debris guard for the microphone and receiver ports employed Gore-Tex™ material (# VE00105 manufactured by W. L. Gore &amp; Associates of Elkton, Md.) for guard member and polypropylene plastic (#100-8932 distributed by Henry Schein/ZAHN of Esschem of Port Washington, N.Y.) for the body of the guard cap. The guard member material was approximately 0.2 mm in thickness. 
     A large-sized sealing retainer was fabricated using the above mentioned polymer foam material and fabrication process. 
     The device, excluding the retainer seal, weighed 0.73 grams, including the 10A battery which weighed 0.29 grams alone. 
     The subject was provided with a control magnet, in the shape of a bar, for remotely switching the device on or off as desired. 
     The acoustic response of the prototype device was measured in a standard CIC coupler (Manufactured by Frye Electronics) and plotted in  FIG. 9 . The response was measured without debris guard (thick solid line labeled No Moisture Guard), with receiver guard (solid line labeled Moisture Guard on Receiver Only), and with debris guards on both receiver and microphone (dotted line labeled Moisture Guard on Receiver and Microphone). 
     Results And Conclusion 
     There was a slight sound degradation (approximately 4 decibels (dB)) at frequencies of 3000 and above compared to the No Moisture Guard condition. However, this represents a minimal acoustic impact which can be easily compensated for electronically or by the employment of thinner guard material. 
     The prototype device, including receiver and microphone debris guards according to the embodiment of  FIG. 5 , and the sealing retainer, was worn deeply and completely inconspicuously in the ear canal of the 55 year old subject. The tip of the receiver was approximately 2-3 mm from the tympanic membrane. The volume trimmer was adjusted in situ by a miniature screwdriver until the preferred volume level was reached for the subject who reported good sound fidelity and comfort of wear. The device was worn comfortably during sleep. The subject was also able to shower while the device was in the ear canal without adverse affects on the perceived quality of sound. 
     It should also be noted that the moisture-proofing provided by the debris guards and enclosures according to the invention can even afford the wearer the opportunity to engage in normal swimming without fear of damage to or loss of fidelity of the hearing device. It would not be recommended that the wearer engage in diving or prolonged underwater swimming, however. 
     It is also worth emphasis that the sealing retainer itself provides significant advantages for use with a semi-permanent hearing device adapted to be inserted entirely within the ear canal of a wearer past the aperture. The sealing retainer is configured for concentric positioning over a medial part of a core assembly of the hearing device so that the core assembly extends laterally within and makes minimal or no contact with the walls of the cartilaginous region of the ear canal. The core assembly is suspended within and snugly supported at the medial part by the sealing retainer, and is arranged and adapted to protrude medially beyond the sealing retainer in a preferred embodiment. The sealing retainer is further configured for seating securely within and occluding the bony region of the ear canal when the semi-permanent hearing device is fully inserted within the ear canal of the wearer. The sealing retainer is sufficiently soft and yielding to conform itself to the shape of the ear canal in the bony region. 
     Consequently, the sealing retainer provides acoustic sealing of the bony region to prevent feedback, and the lateral extension of the core assembly avoids substantial interference with hair and production of cerumen and debris in the cartilaginous region. 
     According to another aspect of the invention, in a method of testing a hearing-impaired individual&#39;s tolerance to long-term wearing of a semi-permanent hearing device inserted entirely within the ear canal past the aperture thereof, the testing is performed without requiring the individual to actually wear the entire hearing device. The method includes a first step of inserting the sealing retainer into the ear canal, with the air cavity of the retainer unoccupied by the core assembly, until the retainer is seated securely against the walls in the bony region. The sealing retainer is removed from the ear canal after having been worn by the individual for a period of sufficient length to determine the long-term tolerance. The individual is interviewed to assess his or her view of the level of comfort and sensitivity to the presence of the device in the ear canal. The ear canal is also examined after removal of the sealing retainer. 
     It is highly desirable to maintain an inventory of assorted sizes and shapes of the sealing retainer for selection of an appropriate fit for the ear canal of the individual. 
     Although a presently contemplated best mode of practicing the invention has been described herein, it will be recognized by those skilled in the art to which the invention pertains from a consideration of the foregoing description of presently preferred and alternate embodiments and methods of fabrication and use thereof, that variations and modifications of this exemplary embodiments and methods may be made without departing from the true spirit and scope of the invention. Thus, the above-described embodiments of the invention should not be viewed as exhaustive or as limiting the invention to the precise configurations or techniques disclosed. Rather, it is intended that the invention shall be limited only by the appended claims and the rules and principles of applicable law.