Magnetic Recording/Audiocassette - The Discovery Of Electromagnetism, Recording On Tape With An Electromagnet, Operation Of The Playback Head
information recorded signal
Audiocassette tape recorders are widely used to record and play back music or speech. Information is stored on a narrow ribbon of plastic tape that has one side coated with a magnetic material, such as iron oxide. An electromagnet aligns individual magnetic particles in a pattern that corresponds to the loudness and frequency of incoming sounds. In order to play back the recorded information, the magnetic tape moves past a pickup coil that generates an electrical output signal. After being amplified, this signal causes a speaker to vibrate which produces sound waves for the listener. A tape recording can be erased by using a rapidly changing magnetic field that scrambles previously recorded patterns of particle alignment.
Additional Topics
Before 1820, magnetism and electricity were two completely separate fields of science. Magnetism was associated with the attraction of magnets for iron objects and the use of a compass needle to locate north and south. Electricity was of practical interest in connection with the hazards of lightning. Some scientists experimented with static electricity in the laboratory by rubbing a wool cloth aga…
Information becomes stored on magnetic tape as it passes by the so-called recording head, which is a small electromagnet. There must be a narrow gap in this electromagnet so that its magnetic field will extend over the nearby section of tape. The signal coming from the audio input is an alternating, back-and-forth current. An audio sound with a frequency of 1,000 cycles per second, for example, re…
How can the information, which was stored in a pattern of magnetically aligned particles on tape, be converted
Figure 2. Cassette and heads. Illustration by Hans & Cassidy. Courtesy of Gale Group.
back into sound waves? The magnetic pattern must be transformed into an electric current, which then can be amplified and cause a speaker to vibrate. The operation of the playback is bas…
In an audiocassette player, the tape must move from the supply reel to the take-up reel at constant speed. Otherwise the sound becomes distorted. It would not work to pull the tape along simply by rotating the take-up reel, because each successive revolution would pull a longer section of tape past the heads, causing the tape speed to increase. To obtain a constant tape speed, a motor is used to t…
The first working model of a magnetic recording device was demonstrated in 1898 by a Danish engineer named Valdemar Poulson. He used the mouthpiece from a telephone to convert speech into an electric current. The current went to an electromagnet which recorded the signal on a thin steel wire. The wire moved past the electromagnet very rapidly, a hundred times faster than modern cassette tapes. Rec…
Citing this material
Please include a link to this page if you have found this material useful for research or writing a related article. Content on this website is from high-quality, licensed material originally published in print form. You can always be sure you're reading unbiased, factual, and accurate information.
Highlight the text below, right-click, and select “copy”. Paste the link into your website, email, or any other HTML document.
User Comments