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Communications

Making Steel Speak

Lessons from Innovations Past

This year marks the centennial of the invention that brought down Richard Nixon and caused complications for Bill Clinton: magnetic recording. It was 100 years ago that Valdemar Poulsen, an engineer with the Copenhagen Telephone Company, applied for a patent on his “telegraphone,” a device that recorded the human voice magnetically on a steel piano wire.

Using the 1898 model of the Poulsen telegraphone (shown above), one could capture a 45-second message on a 100-meter wire wound on a rotating cylinder; the playback sound was free from the characteristic scratching of the phonograph. Poulsen’s invention earned a grand prize at the Paris Exhibition of 1900, but a half-century would pass before magnetic recording found wide-spread application.

There were several technical and business reasons for this delay, but foremost among them was Poulsen’s choice of recording material: solid steel. In early recorders, an electromagnetic head translated the electrical signal from a microphone into a magnetic signal-a steel wire or tape passing by the head picked up a magnetic history of the sound. But steel has poor magnetic properties, so the recorders had to move several feet of steel tape or wire per second, a cumbersome and sometimes dangerous proposition. A crucial step in the evolution of magnetic recording was German chemist Fritz Pfleumer’s 1927 development of a paper tape coated with powdered steel particles. This soon evolved into a plastic tape coated with particles of iron oxide and became the recording medium for AEG’s “magnetophon,” a superior German machine brought to the United States as booty by soldiers returning from World War II.

In 1947, the Bing Crosby radio show was recorded on a captured magnetophon, and magnetic sound recording quickly became a staple of the radio, music and motion picture industries. Magnetic data recording was an important part of the earliest electronic computers, and magnetic video recording, introduced in 1956, rapidly became important to the television industry. In its second half-century, magnetic recording in various forms, now including even ATM cards and hotel room keys, has grown to be ubiquitous in modern society.

Poulsen had originally intended his telegraphone to be used as a telephone answering machine, but for years AT&T executives opposed this application, fearing that many people would not use telephones if they thought their conversations might be recorded. Perhaps they had a point-just ask Monica Lewinsky.

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