Headphones , also called earphones, are a device used for listening in private to various types of equipment that reproduce sound. Such equipment includes cellular telephones, compact disc players, digital music players, radios, and tape recorders. Headphones typically provide one earpiece for each ear and can reproduce stereophonic sound (see Stereophonic sound system (Speakers) ). Most headphones fall into one of three categories. Circumaural headphones have earpieces that form an airtight seal around the ears. Supra-aural headphones have earpieces that rest loosely on top of the ears. Intra-aural headphones, also called earbuds, have small earpieces that fit inside the ears.
All headphones receive electrical signals from some type of sound-reproduction equipment and convert the signals into sound. Thus, headphones serve as miniature speakers (see Speaker ). Various kinds of headphones work by means of different mechanisms. But nearly all such mechanisms function in much the same way.
Most headphones have three main parts: (1) a coil of wire called a voice coil, (2) a cone-shaped piece of plastic called a diaphragm, and (3) a permanent magnet. The voice coil is attached to the diaphragm. The permanent magnet is near the voice coil. When electrical signals pass through the voice coil, they produce varying magnetic forces in the coil that interact with the magnetic forces of the permanent magnet. These forces drive the coil alternately back and forth along the permanent magnet. The coil moves back and forth so rapidly that it vibrates. The motion of the coil moves the diaphragm. The diaphragm’s motion, in turn, produces vibrations in the air, which the ear hears as sound.
The famous American inventor Alexander Graham Bell made the first earphone in 1876. It formed part of the first telephone.
See also Telephone (The speaker ) .
