Electrical audio signal processing systems and devices – Sound effects – Reverberators
Patent
1991-03-05
1993-04-06
Ng, Jin F.
Electrical audio signal processing systems and devices
Sound effects
Reverberators
181130, 181135, H04R 2500
Patent
active
052010074
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to hearing aids and, more particularly, to earmolds that convey amplified sound from the hearing aid to the ear.
Audiologists have long sought to provide an earmold for a hearing aid that prevents the amplified sound from feeding back and interfering with the operation of the hearing aid and, simultaneously, to provide an earmold that is comfortable to wear. The hearing aid art is replete with devices that are able to meet one, but not both, of these objectives.
Feedback is the distortion of amplified sound caused by conduction of the amplified sound back to the microphone that receives the unamplified sound. Conduction occurs through the air pathway between the microphone and receiver in the hearing aid (acoustic feedback), and through the contact between the receiver and the surrounding housing (mechanical feedback). For hearing aid users with a profound hearing loss at several or all frequencies, the acoustic feedback problem is exacerbated by the need to generate abnormally loud sounds in the ear canal. For users with a partial hearing loss (for example, loss of hearing at high frequencies), resolution of the acoustic feedback problem is complicated by the need to amplify sound at some frequencies and to leave other frequencies unamplified.
The parts of the ear's anatomy pertinent to this invention are shown in FIG. 1. The ear canal 10 extends from the ear aperture 20 to the tympanic membrane 30. While canal size and shape may vary from person to person, it is generally about 24 millimeters long and has an S-shape. In cross section it is an oval with the major axis in the vertical direction near the aperture 20 and in the horizontal direction near the tympanic membrane 30. The cross-sectional area of the canal decreases at the isthmus 40 approximately 18 millimeters from the aperture. The canal is formed from cartilage 12 and bone 16 and is lined with skin. The cartilaginous portion is nearest the aperture 20 and is about 8 millimeters long. The osseous portion, formed from the temporal bone 16, is about 16 millimeters long. The temporal bone 16 also contains the cavities of the middle and inner ear. The region outside the ear canal adjacent the aperture 20 forms a bowl known as the concha 50.
Both the ear's anatomy and an incomplete understanding of the hearing process contribute to the failure to produce a hearing aid for both profound and partial hearing loss that comfortably reduced acoustic feedback. It is known, however, that the bones in the skull play an important role in hearing. The ear receives sound waves through the mechanisms of air conduction and bone conduction. Sound waves in the air move through an air conduction pathway (the ear canal) to the tympanic membrane, where they are conveyed to the inner ear. Sound waves also are received by the temporal bone of the skull and conveyed directly to the inner ear. In the inner ear sounds from both sources are joined to produce the full frequency spectrum of hearing. It is believed that the process of hearing may also include the reception of the pressure of acoustic waves on various neural receptors in the body which are relayed to the brain for interpretation along with the inner ear's signals.
Even if the body's methods for receiving and interpreting the various sensory signals which produce hearing were completely understood, and they are not, the hearing process is further complicated by the fact that the major signal source, the inner ear, receives acoustic signals which are complex waveforms dependent upon the size, shape, porosity, et cetera of the ear canal and its surrounding tissue. Sounds received within the ear canal are reflected, refracted and, in part absorbed by the ear canal and its surrounding structure. The sound which arrives at the ear drum has been altered by the various wave reflections and refractions within the ear canal and the head. Thus, the normal open-ear hearing process includes complex and little understood phase relationships among sounds arriving from
REFERENCES:
patent: 2939923 (1960-06-01), Henderson
patent: 3209082 (1965-09-01), McCarrell et al.
patent: 4375016 (1983-02-01), Harada
patent: 5031219 (1991-07-01), Ward et al.
MacAllister M. Duncan
Ward Gary L.
Epic Corporation
Lefkowitz Edward
Ng Jin F.
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