Hearing aid is an electronic device used by those who are hard of hearing, to amplify sounds particularly speech. It’s essential components are a microphone, an electronic amplifier and a receiver, all operated by a battery. In simple terms, the hearing aid can be likened to a miniature public address system. Sounds are amplified by the amplifier and the output is fed to the receiver.
The gain and amplification of the device is determined by the amplifier. In fact, there are low gain, moderate gain and high gain hearing aids. We know that sound signals are wave patterns in which air molecules vibrate, and waves representing different sounds differ in their wave length (and frequency).
As the human ear can selectively respond to certain frequencies very well and not so well to others, manufacturers vary the frequency response of hearing aids with electronic filters, based on the audiometric configurations (low frequency, high frequency or flat loss of hearing) of the user.
Externally most of the aids are provided with a battery compartment, on- off switch, tone control (to adjust the frequency response) and a volume control (to adjust amplification).
In some aids the on-off switch will be provided with a telephone setting to enable the individual to use the telephone. This is made possible with a telecoil in the aid which selectively picks up telephone signals.