Cindy Clark, age 15, of Spokane, Wash., for her question:
HOW DOES A TAPE RECORDER WORK?
There are three main types of audio tape recorders: the reel to reel, the cassette and the cartridge. A stereophonic tape recorder may be any one of the three main kinds.
Most tape recorders can both record and play back tape recordings. The tape on which the recordings are made is a thin plastic ribbon coated on one side with particles of iron oxide or some other substance that is easily magnetized.
When electric audio waves are fed into a tape recorder, they magnetize the particles of iron oxide on the tape in varying patterns. When the tape is played back, the magnetic patterns produce electric signals that are changed back into sounds.
A basic tape recorder has nine parts: (1) a supply reel, (2) a take up reel, (3) a capstan, (4) a pinch roller, (5) an erase head, (6) a recording head, (7) a recording amplifier, (8) a playback head and a (9) playback amplifier.
One end of a tape is taken from the supply reel and is attached to the take up reel. Between the two reels is a soft rubber roller called the pinch roller which presses the tape tightly against a metal rod called the capstan. As a motor turns the capstan, tape is pulled from the supply reel. The take up reel gently pulls on the tape and winds it up. Before it reaches the capstan, however, it touches the erase head which clears it, and then it touches the recording head.
A tape recorder’s recording head is an electromagnet. Here you’ll find a small gap between the poles of the magnet. The electromagnet is magnetized by electric waves from a microphone, and the waves are then strengthened by a recording amplifier. A magnetic field is created in the gap between the magnet’s poles.
As the tape crosses the recording head, it touches the head at the gap. The changing magnetic field magnetizes the particles on the tape in a pattern like that of the sound waves entering the microphone. As soon as the recording,is completed, it can be played back. The magnetic recording on the tape lasts until it is erased.
For playback, the tape is run through the recorder again but this time a playback head is switched on. It picks up the tape’s magnetic pattern which creates electric waves in an electromagnet inside the head. The playback amplifier strengthens these waves enough to operate a loudspeaker which changes them into sound.
Cassette tape recorders are in most ways small copies of reel to reel recorders. But they are easier to operate because the tape does not have to be threaded through.
A cassette recorder uses a small plastic case called a cassette. Inside the cassette are a supply reel, which holds the tape, and a take up reel. The cassette is snapped into the recorder and is ready to use. Although cassettes use tape that is only an eighth of an inch wide, they can carry up to four tracks.