Hearing Aid Transducers

Abstract

This chapter contains a brief historical and descriptive review of the microphones, earphones, and bone vibrators that are the essential elements in a hearing aid. The dramatic reduction in size of microphones and earphones (receivers) is documented, as is their improved performance with time. A discussion of their theoretical performance (sensitivity, noise, and output) versus size is followed by a comparison of theory and practice. The practical effects of microphone location about the ear and ear-tip location in the ear canal, and recent improvements in the ability to measure hearing aids, end the section on microphones and receivers. The final sections, on bone vibration history and progress, cover the progress to direct-to-bone vibrators.