The hearing aid system

Abstract

A hearing aid is simply a miniature public address system (Figure 5.1). Sound waves strike a microphone, which converts energy into a weak electrical signal. The signal is fed into an amplifier. The amplifier signal is used to drive a loudspeaker, which converts the electrical signal back into acoustic energy. The sound waves generated are then `piped' into the external ear canal. The acoustic energy delivered to the ear is always greater than that received by the microphone. This additional energy is provided by the battery.