How it began
Valdemar Poulsen, born in Copenhagen in 1869, worked in the technical section of the Copenhagen Telephone Company. In 1898 he recorded his own voice by feeding the signal from a telephone microphone to an electromagnet that he moved along a steel piano wire. He applied for a patent, and in 1899 he founded a company to build the machine, which he called the Telegraphone.
Before it existed
Sound recording meant Edison's mechanical phonograph. The American inventor Oberlin Smith had experimented with magnetic recording on steel wire and on threads loaded with steel dust in 1878, but he did not complete a working machine. In 1888 he offered the idea to the public in an article in the magazine Electrical World.
How it works
A microphone signal drives an electromagnet, which magnetizes a moving steel wire in a pattern that follows the sound. Britannica describes it as an electromagnetic phonograph that registers speech by alternating magnetization of a wire. One version held up to 30 minutes of audio on wire wound around a cylinder, and a simple version stored 2 minutes on a steel disk about 5 inches across. It was conceived as a telephone answering machine.
How it spread
A working model drew great interest at the 1900 Paris exposition, where it won a Grand Prix and recorded Emperor Franz Josef of Austria. The American Telegraphone Company took up Poulsen's design for a dictating machine in the following years. Wire recorders found limited acceptance until vacuum tube amplifiers were developed.
What lasted
From the 1920s companies in Germany, Britain and the United States built generations of magnetic recorders for radio broadcasting and military use. Steel tape developed in the 1930s improved sound quality and stayed in use at the BBC and other broadcasters into the 1950s, when lower-cost tape replaced it.
