How Does a Tape Recorder Work?
Introduction
Tape recorders are devices used to record and play back audio signals stored on tape inside of plastic cassettes. Sound vibration causes movement of the diaphragm in the microphone, which creates electrical pulse patterns. The pulses flow through electromagnets that touch a moving tape encased in a plastic cassette. The tape is coated with a metal powder, which changes with fluctuations of the magnetic field. Each fluctuation represents a sound that is recorded on the tape permanently unless erased or overwritten. Playing back a tape works in the opposite way, with tape signals flowing to the tape head, creating electrical pulses that are boosted before being sent to the speakers.
History
The first recording tape was created by Friedrich Matthias of IG Farben/BASF in Germany in 1935. Magnetic tape recorders were developed in the 1940s by the Brush Development Company, and magnetic tape media was developed by the Minnesota Mining and Manufacturing Company.
The Tape
Tape is comprised of a thin plastic film that is coated with a metallic and magnetic powder, usually ferric oxide powder. The powder is combined with a binder material to attach it to the tape and a dry lubricant to protect the recorder. Different qualities are produced, depending on the metal coating; from standard to best, there is ferric-oxide, ferric-oxide particles mixed with chromium dioxide, and metallic particles rather than metal-oxide particles are used in the tape. Metal tapes offer the best sound quality but need special recorders to record; they can be played back on any player. Tape can be encased in a variety of media formats, from reel-to-reel and 8-track to cassette tapes, which were patented in 1964. Cassette tapes are flat, rectangular shells with the tape wrapped around two spools of tape that are spun. Small felt pads provide a backstop for the record and playback head in tape recorders.
Tape Recorder
The outside of tape recorders come in many sizes and shapes, but the internal mechanisms operate on the same principles. Tiny electromagnets add a magnetic flux, or charge, to the surface of the metal-coated tape as it slides over the electromagnets, which are iron cores wrapped in wire. An audio signal is sent through the wire, creating a magnetic field in the core that magnetizes the metal coating on the tape. During playback, the tape creates a magnetic field in the core and a signal in the coil is amplified through speakers. Usually tape recorders have two tiny electromagnets that are each a quarter the width of the tape for stereo sound. When the tape is turned over, the other half of the tape touches the electromagnets. The cassette is snapped into the tape recorder so that the two sprockets of the recorder fit into the two holes on either side of the cassette. The sprockets are spindles with square edges that fit snugly against the teeth of the spools of tape within the cassette, so when the sprockets spin in the same direction, the cassette spools both turn and pull the tape from one reel to the other across the electromagnets. Two heads below the two sprockets, one used to erase the tape clean of signals before recording and the other contains the record and playback electromagnets.
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