Valdemar Poulsen (23 November 1869 – 23 July 1942) was a Danish engineer who developed a magnetic wire recorder.
- Telegraphone, a magnetic wire recorder (1899)
As early as 1888, Oberlin Smith, at one time president of the American Society of Mechanical Engineers, proposed that sound could be recorded by magnetizing iron particles that adhered to a carrier. He was too busy to implement his idea, however, and the ball passed to Valdemar Poulsen, a young Danish engineer who accidentally discovered that patterns traced on the side of a magnetized tuning fork became visible when the fork was dipped in iron powder. When the fork was demagnetized, the patterns were erased. He saw in the imprinting and erasure of these patterns the possibility of a recording device for sound, using iron wire as the carrier. Its immediate commercial use, he imagined, would lie in providing tangible records of telephone conversations. He called the device a "Telegraphone," which he understood to signify "writing the voice at a distance."
Poulsen obtained a Telegraphone Patent in 1899, and with his assistant, Peder O. Pedersen, later developed other magnetic recorders that recorded on steel wire, tape, or disks. None of these devices had electronic amplification, but the recorded signal was easily strong enough to be heard through a headset or even transmitted on telephone wires.
At the 1900 Paris Exposition, he won the Grand Prix for his invention. Despite extensive publicity, however, he was not able to raise the necessary capital in Europe for its development. By 1903 the patents had passed to the American Telegraphone Company (ATC), which raised a huge amount of money ($5,000,000) by selling stock. Five years later the owners of ATC had still not built a single machine. Their main business, in fact, turned out to be raising money for the machines rather than actually producing the ma- chines. When they did finally tum out a few operational devices in 1911, using the famous model Phoebe Snow to advertise them as dictation ma- chines, the sound quality was so bad that the Dupont Company, after installing them in a central dictation system, ended up suing. The questionable status of the machines was exacerbated during World War I, when the Telefunken Company of America was accused of using them to encode and transmit secret messages to Germany.
- Arc converter (1902)
In 1902, Poulsen improved an arc converter developed by William Du Bois Duddell (1899), which was widely used in radio (in Germany by Lorenz A.G. company) before the advent of vacuum tube technology (by Alexander Meißner in 1913).
- A notice about Poulsen in Popular Mechanics, June 1907.
- F.J. Mann, "Federal Telephone and Radio Corporation. A Historical Review 1909-1946", Electrical Communication, Vol. 23, Dec 1946, pp 377-405.
- Absalon Larsen, Telegrafonen og den traadløse og Opfinderparret Valdemar Poulsen og P.O. Pedersen, 1950.
- K. Dannefelt Bøthner, "Valdemar Poulsen, 1969. (Danish)
- Hugh Aitken, The Continuous Wave, Princeton, 1985.
- Dave Fowler, "Ocean Beach Wireless Transmitting Station", 15 June 1996.
- Louis Nielsen, "Valdemar Poulsen og telegrafonen: Opfindelsen af magnetisk lagring", December 2003. (Danish)
- Hayles, N. Katherine (1999). How We Became Posthuman: Virtual Bodies in Cybernetics, Literature, and Informatics. University of Chicago Press. pp. 350.
- Aaron Foisi Nmungwun, "The Origin of Magnetic Recording", in Video Recording Technology: Its Impact on Media and Home Entertainment, Routledge, 2012.