A device that converts sound waves into analogous electrical waves. Usually called a "mike," it contains a flexible diaphragm composed of film or foil that vibrates as it makes contact with the sound. The diaphragm movement modulates an electrical current by various methods. In a carbon mike, used in telephones for more than a hundred years, the diaphragm alters the pressure in carbon grains, changing its resistance.
Condenser Microphones
In a condenser mike, also called an "electrostatic mike" or "capacitor mike," the diaphragm changes the capacitance between itself and a metal plate, both acting as electrodes. The widely used electret mike has a charged dielectric between the electrodes that generates voltage.
Crystal and Dynamic Microphones
Crystal microphones use a piezoelectric diaphragm that produces voltage when subjected to the sound waves (mechanical pressure).
Dynamic mikes, which are like speakers in reverse, use a diaphragm attached to a movable coil that generates voltage as air moves the coil between the poles of a magnet.
