loudspeaker or speaker, device used to convert electrical energy into sound. It consists essentially of a thin flexible sheet called a diaphragm that is made to vibrate by an electric signal from an amplifier . The vibrations create sound waves in the air around the speaker. In a dynamic speaker, the most common kind, the diaphragm is cone-shaped and is attached to a coil of wire suspended in a magnetic field produced by a permanent magnet. A signal current in the suspended coil, called a voice coil, creates a magnetic field that interacts with the already-existing field, causing the coil and the diaphragm attached to it to vibrate. To provide a faithful reproduction of music or speech, a loudspeaker must be able to reproduce a wide range of audio frequencies (i.e., 20 Hz to 20 kHz). Since it is difficult for a single speaker to do that adequately, many quality sound systems employ speakers of three different sizes. The largest ones, or woofers, reproduce low frequencies; the medium-sized ones, or midrange speakers, reproduce middle frequencies; the smallest ones, or tweeters, reproduce high frequencies. The three sizes were traditionally contained in the same cabinet, with a pair of such speakers used for stereophonic sound , but increasingly in the late 1980s and early 1990s home sound systems used smaller pairs of speakers enclosures containing only the midrange speakers and tweeters and a single woofer cabinet designed to be placed in an out-of-the-way location. This design takes avantage of the fact that the human ear is not good at determining the direction of low-frequency sound, and thus stereo perception is not adversely affected by the location of the woofer. A crossover network is a filter in a speaker system that ensures that each speaker receives only signals in the frequency range it is designed to reproduce. A properly designed enclosure can reduce unwanted resonances and extend the frequency range of a speaker system. Along with dynamic speakers, other speaker types include electrostatic and piezoelectric.
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.
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