Canal hearing device with tubular insert

Details Canal hearing device with tubular insert Canal hearing device with tubular insert

1999-04-29

2004-04-20

Kuntz, Curtis (Department: 2643)

Electrical audio signal processing systems and devices

Hearing aids, electrical

Specified casing or housing

C600S025000, C607S056000, C607S057000, C381S322000, C381S325000, C381S323000, C381S329000, C381S324000

Reexamination Certificate

active

06724902

ABSTRACT:

BACKGROUND OF THE INVENTION
A. Technical Field
The present invention relates to hearing devices, and, more particularly, to miniature hearing devices that are deeply positioned in the ear canal for improved energy efficiency, sound fidelity, and inconspicuous wear.
B. Description of the Prior Art
Brief Description of Ear Canal Anatomy
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 25 mm in length from the canal aperture
17
to the tympanic membrane
18
(eardrum). The lateral (away from the tympanic membrane) 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. The medial (towards the tympanic membrane) 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 more sensitive to touch or pressure. There is a characteristic bend
15
that roughly occurs at the bony-cartilaginous junction
19
, which separates the cartilaginous
11
and the bony
13
regions. The magnitude of this bend varies significantly among individuals. The internal volume of the ear canal between the aperture
17
and tympanic membrane is approximately 1 cubic centimeter (cc).
A cross-sectional view of the typical ear canal
10
(
FIG. 2
) reveals generally an oval shape and pointed inferiorly (lower side). The long diameter (D
L
) is along the vertical axis and the short diameter (D
S
) is along the horizontal axis. Canal dimensions vary significantly among individuals as shown below in the section titled Experiment A.
Physiological debris
4
in the ear canal is primarily produced in the cartilaginous region
11
, and includes cerumen (earwax), sweat, decayed hair, and oils produced by the various glands underneath the skin in the cartilaginous region. There is no cerumen production or hair in the bony part of the ear canal. The ear canal
10
terminates medially with the tympanic membrane
18
. Laterally and external to the ear canal is the concha cavity
2
and the auricle
3
, both also cartilaginous.
Several types of hearing losses affect millions of individuals. Hearing loss particularly occurs at higher frequencies (4000 Hz and above) and increasingly spreads to lower frequencies with age.
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) Behind-The-Ear (BTE) type which is worn behind the ear and is attached to an ear mold which fits mostly in the concha; (2) In-The-Ear (ITE) type which fits largely in the auricle and concha cavity areas, extending minimally into the ear canal; (3) In-The-canal (ITC) type which fits largely in the concha cavity and extends into the ear canal (see Valente M.,
Strategies for Selecting and Verifying Hearing Aid Fittings
. Thieme Medical Publishing. pp. 255-256, 1994), and; (4) Completely-In-the-Canal (CIC) type which fits completely within the ear canal past the aperture (see Chasin, M.
CIC Handbook
, Singular Publishing (“Chasin”), p. 5, 1997).
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 canal devices (ITC and CIC devices are collectively referred to herein as canal devices), 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 (Chasin, pp. 10-11).
However, even with these significant advances leading to the advent of canal devices, there remains a number of fundamental limitations associated with the underlying design and configurations of conventional canal device technology. These problems include: (1) oscillatory (acoustic) feedback, (2) custom manufacturing and impression taking, (3) discomfort, (4) occlusion effect and, (5) earwax. These limitations are discussed in more detail below.
(1) Oscillatory feedback occurs when leakage (arrows
32
and
32
′ in
FIG. 3
) from sound output
30
, typically from a receiver
21
(speaker), occur via a leakage path or a vent
23
. The leakage (
32
′) reaches a microphone
22
of a canal hearing device
20
causing sustained oscillation. This oscillatory feedback is manifested by “whistling” or “squealing” and is not only annoying to hearing aid users but also interferes with their communication. Oscillatory feedback is typically alleviated by tightly occluding (sealing) the ear canal. However, due to imperfections in the custom manufacturing process (discussed below) or to the intentional venting incorporated within the hearing device (also discussed below) it is often difficult if not impossible to achieve the desired sealing effect, particularly for the severely impaired who require high levels of amplification. Oscillatory feedback primarily typically occurs at high frequencies due to the presence of increased gain at these frequencies.
(2) Custom manufacturing and impression taking: Conventional canal devices are custom made according to an impression taken from the ear of the individual. The device housing
25
(FIG.
3
), known as shell, is custom fabricated according to the impression to accurately assume the shape of the individual ear canal. Customizing a conventional canal device is required in order to minimize leakage gaps, which cause feedback, and also to improve the comfort of wear. Custom manufacturing is an imperfect process, time consuming and results in considerable cost overheads for the manufacturer and ultimately the hearing aid consumer (user). Furthermore, the impression taking process itself is often uncomfortable for the user.
(3) Discomfort, irritation and even pain frequently occur due to canal abrasion caused by the rigid plastic housing
25
of conventional canal devices
20
. This is particularly common for canal devices that make contact with the bony region of the ear canal. Due to the resultant discomfort and abrasion, hearing devices are frequently returned to the manufacture in order to improve the custom fit and comfort (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).
(4) The occlusion effect is a common acoustic problem caused by the occluding hearing device. It is manifested by the perception of a person's “self-sounds” (talking, chewing, yawning, clothes rustling, etc) being loud and unnatural compared to the same sounds with the open (unoccluded) ear canal. The occlusion effect is primarily due to the low frequency components of self-sounds and may be experienced by plugging the ears with fingers while talking for example. The occlusion effect is generally related to sounds resonating within the ear canal when occluded by the hearing device. The occlusion effect is demonstrated in
FIG. 3
when “self-sounds”
35
, emanating from various anatomical structures around the ear (not shown), reach the ear canal
10
. When the ear canal is occluded, a large portion of self-sounds
35
are directed towards the tympanic membrane
18
as shown by arrow
34
. The magnitude of “occlusion sounds”
34
can be reduced by incorporating an “occlusion-relief vent”
23
across the canal device
30
. The occlusion-relief vent
23
allows a portion of the “occlusion sounds”
35
to leak outside the ear canal as shown by arrow
35
′. The occlus

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