The simplest type of hearing aid is the ear trumpet, used by the hard of hearing since ancient times. Even a hand held behind the ear can assist hearing, as it assists the outer ear or pinna in collecting sound waves so that they enter the external ear canal. If you have read many hearing aid reviews, you would know that many aids can actually improve hearing by almost 80%.
The battery-operated hearing aid consists of three main components. A microphone picks up the sound waves and converts them into an electrical impulse. These impulses are amplified by an electrical circuit, and then converted back into sound by the ‘speaker’. The amplification circuit often includes a loudness control. In order to maximize efficiency, the amplified sound is directed into the ear canal by a simple earphone (as used in a transistor radio), or a specially molded earpiece that fits tightly into the inner part of the pinna. If the deafness is primarily conductive in nature, a special attachment which fits tightly over the bone behind the ear is used instead of an ear piece.
There was little development of hearing aid prior to the Second World War. The main limitation was the electronic parts needed to produce suitable amplification of sound. In the earliest hearing aids, small valves to be used, but they required large high voltage batteries in order to work. The microphone and electronic circuit were enclosed in a relatively large container (usually bigger than a packet of cigarette), normally worn in a coat or shirt pocket. Long cords conducted the amplified sound to the ears.
Advances in hearing aids With the development of transistors, the power supply and electronic circuit became miniaturized. Today hearing aid can be fitted into or behind the ear, with a tiny mercury battery providing the power source. These parts may be incorporated into a pair of spectacles, making the hearing aid almost unnoticeable. The development of ‘silicon chips’ will probably mean further advances which will enable models to be fitted totally in the ear.
Many types of hearing aids are available commercially. More elaborately designed models have special circuits to enhance sounds of which the pitch falls within the range of normal speech. There are also special ‘induction coils’ that can pick up and amplify the electrical impulses in a telephone, thus bypassing the microphone and resulting in less distortion.
Larger hearing aids are used during speech training of deaf children. They usually wear large headphones, ‘plugged in’ to the teacher.
The National Acoustic Laboratories run by the federal government, supplies hearing aids free of charge to all children and pensioners. When someone complains of hearing loss, hearing tests are undertaken to determine the type and degree of deafness. Treatable causes such as infection and wax blocking the ear canal are dealt with and those people whose hearing loss cannot be resolved are fitted with the type of aid best suited to their needs.