microphone

Primary component in a sound-reproducing system, whereby the mechanical energy of sound waves is converted into electrical signals by means of a transducer. In one type, a diaphragm is attached to a coil of wire placed between two poles of a permanent magnet. Sound waves cause the diaphragm to vibrate, which in turn causes the coil of wire to move in the magnetic field of the permanent magnet. An induced electrical current, matching the pattern of the sound waves, flows through the coil and is fed to an amplifier. The amplified signals are either stored or sent to a loudspeaker.

One of the simplest microphones is the telephone receiver mouthpiece, invented by Scottish-US inventor Alexander Graham Bell in 1876; other types of microphone are used with broadcasting and sound-film apparatus.

Telephones have a carbon microphone, which reproduces only a narrow range of frequencies. For live music, a moving-coil microphone is often used. In it, a diaphragm that vibrates with sound waves moves a coil through a magnetic field, thus generating an electric current. The ribbon microphone combines the diaphragm and coil. The condenser microphone is most commonly used in recording and works by a capacitor.

microphone

Receiver which turns sound into electrical signals. The signals, transmitted and amplified, can also be used for radio, television, or recording purposes, or in theatres and public halls for the relaying of speech, song, and taped sound to amplifiers placed at various points of the building.