Mother's Under-$30 Hearing Aid

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Most of us will no doubt agree that hearing and sight are our two most precious senses . . . so when something goes awry with either, our lives are deeply affected. Indeed, if it becomes severe enough, an impairment of sight or hearing can become a serious disability. You might be surprised to learn, though, that hearing impairment is by far the more prevalent of the two. There are 16,000,000 people in the U.S. alone with admitted deafness . . . and an estimated 16,000,000 more who have a hearing disorder but are unaware of the problem!

In many cases, the hearing impaired can be helped by a device that makes sound louder: a hearing aid. Hearing aids are, in the most general sense, electronic amplifiers that boost sound level to the point where people who are hard of hearing can understand what's being said. It's estimated that about half of all people suffering hearing disorders can gain at least some relief through the use of a hearing aid.

Unfortunately, such devices don't come cheap: It's not unheard-of for certain designs to run into the thousands of dollars. To many of you, that may seem like an awful lot of money to pay for a small amplifier. Well, MOTHER and I agree-to a point-so we've gotten together to show you how to assemble our "volks" hearing aid . . . one that can be built almost entirely from parts available at a local Radio Shack for less than $30. Before you get involved in this project, though, y ou need to know if you can actually benefit from using an amplifier.

HEARING

The manner in which humans perceive sound is a marvelous example of natural engineering. The ear is divided into three areas: the outer, the middle, and the inner ear. The outer ear funnels sound to the drum, a vibrating membrane that transforms those sound pressures into mechanical movement. Attached to the eardrum itself, in the middle ear, is an extremely intricate linkage of three tiny bones that acts as a lever—similar to a piston—to stimulate the hair endings of the cochlea. Inside the cochlea, deep in the inner ear, that mechanical sound is changed into electrical impulses that are then transmitted to the brain through the auditory nerves.

Damage or disease in any of the three areas of the ear can result in hearing loss. There are four basic types of disorders. The first, conductive hearing loss, is caused by disease or obstruction in the outer or middle ear. Conductive hearing impairment usually isn't severe and can often be corrected through surgery or medical treatment.

A sensorineural hearing disorder is caused primarily by damage to the sensory hair cells of the cochlea or to the nerves of the inner ear. The disability may range from mild to profound. Sensorineural damage is usually the result of prolonged exposure to highintensity sounds, such as explosions or factory noises. It's a progressive disease—the degeneration is proportional to the length of exposure—and the impairment generally affects a particular sound frequency range. When losses are greater in some frequency ranges than in others, distortion often results.