microphone

microphone, device for converting sound into electrical energy, used in radio broadcasting, recording, and sound amplifying systems. Its basic component is a diaphragm that responds to the pressure or particle velocity of sound waves. The microphone, various forms of which were developed independently c.1877 by inventors Emile Berliner, David E. Hughes, and Thomas A. Edison, was first used as a telephone transmitter. The carbon microphone, which was used in the first telephones and was very popular in telephones until about 1970, contains loosely packed carbon grains. Sound makes the diaphragm vibrate, causing the grains to be compressed and released, thus changing the resistance of the microphone. That can be exploited by an associated electric circuit. Electrostatic microphones, also called condenser microphones, consist of a fixed electrode (the backplate) and a movable electrode (the diaphragm), with an air gap between them. Sound waves impinge on the diaphragm, making it vibrate, and changing the capacitance formed by the two electrodes. Electret microphones, which are the most widely used microphones, have a permanently charged dielectric between the two electrodes and thus generate voltages when the electrodes vibrate. Crystal microphones generate minute voltages by the piezoelectric effect. Both the dynamic microphone and the rarely used ribbon microphone generate voltages by electromagnetic induction. For example, in the dynamic microphone, the diaphragm is attached to a light movable coil that generates a voltage as it moves back and forth between the poles of a permanent magnet.

Bibliography

See G. M. Ballou, Handbook for Sound Engineers (1991).

---

microphone

In a moving-coil microphone, sound waves cause the diaphragm to vibrate, and this oscillating …

(credit: © Merriam-Webster Inc.)

Device for converting sound waves into electric power that has wave characteristics essentially similar to those of the sound. By proper design, a microphone may be given directional characteristics so that it will pick up sound primarily from a single direction, from two directions, or more or less uniformly from all directions. In addition to their use in telephone transmitters, microphones are most widely applied in hearing aids, sound-recording systems (principally magnetic and digital tape recorders), and public-address systems.

---

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 changes 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.

---

(hardware, audio)

microphone - Any electromechanical device designed to convert sound into an electrical signal. A microphone converts an acoustic waveform consisting of alternating high and low air pressure travelling through the air into a voltage. To do this it uses some kind of pressure or movement sensor. The simplest kind of microphone is actually very similar in construction to a loudspeaker. The analogue electrical signal can be fed into a computer's sound card where it is amplified and sampled to convert it into a digital waveform for storage or transmission.