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hearing aid,device used in some forms of deafness to amplify sound before it reaches the auditory organs. Modern hearing aids are electronic. They contain a tiny receiver and a transistor amplifier, and are usually battery powered. Some are small enough to fit into an arm of a pair of eyeglasses, or into the outer ear. The bone-conduction hearing aid, placed behind the ear, channels sound waves to the adjacent bony part of the skull, which then transmits the vibrations to the auditory nerve of the cochlea. The air-conduction hearing aid amplifies sounds and directs them into the ear toward the tympanic membrane. In recent years, a number of advancements have been made to hearing aids, improving the comfort, sensitivity, and aesthetic quality of the devices. Today, many hearing aids are customized to amplify only those noises (e.g., high frequency) that the user has difficulty hearing. Cochlear implants have been developed for use by certain totally deaf people. They consist of mechanical replacements for ineffective hair cells in the inner ear, which transform sound vibrations into electronic impulses that stimulate the auditory nerve.
a sound-amplifying device used by persons afflicted with deafness or impaired hearing. The earliest hearing aids were purely acoustic devices, such as ear trumpets, whose narrow end was inserted into the ear. Modern hearing aids are electroacoustic devices consisting of a microphone, an amplifier, and an earphone. The sound enters the microphone, where it is converted into electric voltage. Amplified by electronic tubes or transistors, this voltage enters the earphone, where it is reconverted into amplified sound.
Hearing aids differ in design according to the nature of the auditory impairment. The standard earphone, inserted into the ear, transmits amplified sound into the external ear, and the bone conduction receiver, pressed against the mastoid process of the temporal bone, transmits sound into the inner ear.
Miniature hearing aids have a miniature earphone that is attached to an individually molded insert in the external ear. Some hearing aids are built into eyeglass frames or hair clips. Pocket hearing aids are manufactured as well. Hearing aids are prescribed by a physician and individually fitted in specialized laboratories after exhaustive hearing tests.