Stereophonic sound system, often called a stereo, is electronic equipment that reproduces lifelike sound using at least two speaker channels. Stereo sound is contrasted with monaural sound, which has only one channel. Unlike monaural sound, stereo sound seems to have depth and come from a wide area. Most devices designed for listening to recorded sound—from expensive home theater systems to tiny digital music players—can play stereo sound.
Types of systems
Stereos vary widely in shape and size. Some consist of many parts spread over a large room. A portable stereo, on the other hand, may be smaller than a credit card.
Home stereo systems.
The most advanced stereos are called component systems. They consist of individual components (parts) that are purchased separately and connected by the consumer. Component stereo systems often form part of a home theater system, along with a large-screen television. Many component systems use speakers arranged around a room to envelop the listener with sound, an effect called surround sound.
Mini stereo systems have the same basic parts as component systems, preassembled into a single frame or cabinet. They typically cost less than component systems but produce sound that is poorer in quality.
Other stereo systems.
Computers typically include a stereo system, with speakers either built in or connected through an output jack. Many automobiles equipped with a stereo system have two or more sets of speakers mounted throughout the interior. Pocket-sized digital music players can store thousands of songs as computer files and play them through headphones. Some mobile phones function as digital music players.
Parts of a stereo system
Every stereo system has three basic types of parts: (1) a program source, (2) an amplifier, and (3) speakers or headphones. In a large component system, these parts may exist as separate, large units wired together across a room. In most portable systems, the program sources and amplifier are contained in a single, tiny device that connects to headphones.
Program sources
provide electric signals that will be turned into sound. Many program sources “play” sound from various types of recordings, including compact discs (CD’s), DVD’s, and computer files. Program sources produce electric signals from the recordings’ encoded (stored) sound. These electric signals, in turn, represent the shape of sound waves that eventually reach a listener’s ear.
Compact disc (CD) players read sound that has been recorded on a small, round disc in digital (numeric) code. The disc consists of hard plastic with a reflective metal coating. A laser beam shines on the disc, which is spun by the player. The beam reflects off the spinning disc as pulses of light. The CD player uses the pulses, which correspond to the code on the disc, to create an electric signal.
Loading the player...Compact disc
DVD and Blu-ray players serve as common program sources for home theater systems. DVD’s and Blu-ray discs look and work much like a compact disc but usually contain video as well as multiple channels of audio.
Phonographs, also called record players, read recorded sound from plastic discs called records. Jagged waves within a spiral groove on the record form an analog (likeness) of the original sound waves. The record is placed on a circular turntable. As the turntable spins the record, a needle called a stylus rides along the groove. The waves in the groove cause the stylus to vibrate. The phonograph converts the vibrations into electric signals.
Tuners receive signals broadcast from radio stations and convert them into electric signals. Each radio station broadcasts its program signals at a specific frequency (rate of vibration). The user adjusts the tuner to receive a radio signal of a particular frequency. In many stereo systems, the tuner and amplifier combine to form a single unit called a receiver.
Computers and digital music players produce sound from digital audio files. Such files can easily be transferred across multiple devices or over the Internet. A computer program translates the code from such files into electric signals. Most computers and digital music players have amplifiers of their own. But they can also plug into more complex stereo systems, functioning only as a program source.
Amplifiers
strengthen the electric signals from a program source. Stereo systems require at least two amplifier channels—one for each speaker. In general, amplifiers with greater power provide better sound, by lessening distortion. However, speakers are designed to use only a certain range of power. For this reason, the amplifier in a system must be coordinated with the speakers. Too much power from an amplifier can damage speakers. Volume controls adjust the amount of amplification applied to a program source, making it louder or softer.
In addition to amplification, most stereo systems offer various ways of adjusting the sound before it reaches the speakers. Balance controls adjust the relative strength of a stereo’s audio channels, making the right speaker louder or softer than the left. An equalizer controls the tone of sound. There are three basic types of tone controls: bass, midrange, and treble. Bass controls cut or boost low-frequency audio signals, which produce low-pitched, deep and rumbling sounds. Midrange controls alter audio frequencies around the pitch of the human voice. Treble controls affect high-pitched sounds, such as cymbals.
Speakers
convert electric signals from the amplifier into vibrations. These vibrations create the sound waves that people can hear. Stereophonic systems require at least two speakers—one for each channel of recorded sound. The location of speakers in a room also affects the quality of the sound they produce.
Speakers are usually mounted in wooden or plastic cabinets. It is difficult for one speaker element to reproduce the entire range of frequencies. High-quality speaker cabinets thus often contain three separate speakers—one each for bass, midrange, and treble. The size and shape of the cabinet affects the tone quality of the sound from the speakers. Component systems usually include a separate unit, called a subwoofer, for reproducing deep bass sounds. A home theater system may have five or more speakers surrounding a listening area, in addition to a subwoofer.
Headphones are small speakers that fit in or around a person’s ears for private listening. Each earpiece carries one sound channel. Earpieces are often cushioned for comfort. Headphones that fit inside a person’s ears are called earphones or earbuds.
History
Stereophonic phonographs and discs first appeared on the market in 1958. Previously, records and phonographs were monophonic or _monaural—_that is, they reproduced sounds through only one channel. Radio stations began broadcasting programs in stereo on a large scale in 1961. By the late 1960’s, almost all new recorded music was stereophonic.
Until the mid-1980’s, phonographs were the most common program source. Some music fans continue to use phonographs today. Tape decks, which used magnetic cassette tapes as a program source, became more popular in the 1980’s. Unlike phonograph records, many tapes could be easily erased and rerecorded, enabling tape deck users to create custom listening experiences. By the late 1990’s, CD players largely replaced tape decks. Digital music players and audio files became widespread in the 2000’s.
