A device called the carbon transmitter was needed in both the early telephone and the early electric hearing aid. This transmitter was first commercially available in 1898 and was used to electrically amplify sound. In the 1920's, the carbon transmitter was replaced by the vacuum tube, and later by a transistor. Transistors allowed electric hearing aids to become small and efficient.
Old Advertisement for a Mechanical Hearing Aid
Hearing Aids Through the Ages
Hearing aids in their various forms have provided needed amplification of sound for many persons experiencing hearing loss.
Hearing Aid Museum
Since hearing loss is one of the oldest of the known disabilities, attempts to amplify sound go back several centuries.
