Hearing aid

Hearing aid, device to improve hearing by amplifying sound waves. The first hearing aid was a tube called the ear trumpet, a flared tube held up to the ear. The early electronic hearing aid consisted of a small battery-powered amplifier, housed with a microphone in a small case. Signals picked up by the microphone were amplified, then fed via a flexible cord to a small earphone fitting over the ear. Transistors made it possible to reduce the size of hearing aids and to increase efficiency. Modern devices employ advanced microcircuitry and are small enough to be built into spectacle frames or hair slides. Some fit behind the ear and transmit sounds through the bones of the skull, while others are small enough to fit inside the ear.

See also: Ear.