Most consist of a thin diaphragm, the mechanical vibration of which is converted to an electrical signal proportional to the sound pressure. A telephone mouthpiece usually consists of a carbon microphone in which the sound waves exert a varying pressure on carbon granules, so varying their electrical resistance. In capacitor microphones, commonly used in music recording, the diaphragm forms one plate of a capacitor, across which the sound waves produce a fluctuating potential difference. Crystal microphones rely on the piezoelectric effect . Other types use magnetic induction, magnetostriction, or other electromagnetic effects.
Ribbon microphones have a highly directional response.
They consist of a strip of aluminium alloy in a strong magnetic field. The ribbon vibrates in the sound waves, inducing in itself an electromotive force proportional to its velocity. The New Penguin Dictionary of Science 2. The Macmillan Encyclopedia 2001 3. All rights reserved.