"Method of, and apparatus for, effecting the storing up of speech or signals by magnetically influencing magnetisable bodies"
Valdemar Poulsen, son of a Danish High Court judge was born 23rd November 1869. He was not a good scholar; the only subjects he was interested in were physics and drawing. He had no interest in mathematics, a trait he shared with many other great inventors. His father wanted him to become a doctor but after an unsuccessful time at medical school, at the age of 24, he obtained a position in the technical section of the Copenhagen Telephone Company. His work was mainly troubleshooting which allowed him a fair amount of time for experimenting.
There seems to be no record of what gave Poulsen the idea of magnetising steel wire to make sound recordings. Maybe he had read an article written in 1888 by American scientist Oberlin Smith for the magazine Electrical World. In his article Smith discussed the possibility of permanent magnetic impressions for recording sound and suggested, as a medium, cotton or silk thread, in which steel dust was suspended. Smith also considered steel wire but didn't think it would be possible 'that it would divide itself up properly into a number of short magnets" to establish a magnetic pattern as a replica of currents produced by a microphone. Smith never built a machine or proved his theory practically.
In an early experiment Poulsen stretched a steel wire between two parallel walls, inclined at such an angle that a small electromagnet suitably attached to the wire could, assisted by gravity, slide down the wire at a uniform speed. Wires attached to the electromagnet energised it from the voltage of a battery modulated by a microphone. For replay the battery was disconnected, and the microphone replaced by a telephone earpiece, the electromagnet returned to the top and let go. The experiment worked and Poulsen set about putting magnetic recording to use in the shape of a telephone answering machine.
On 1st December 1898, he filed a patent in Denmark for the Telegraphone, the first device in history to use magnetic sound recording. An extract from this patent reads:
"The invention based upon the fact that when a body made of magnetisable material is touched at different points and at different times by an electromagnet included in a telephonic or telegraphic circuit, its parts are subject to such varied magnetic influences that conversely by the action of the magnetisable body upon the electromagnet the same sounds or signals are subsequently given out in the telephone or recording instrument as those which previously caused the magnetic action upon the magnetisable body."
The original Telegraphone consisted of a spirally grooved brass cylinder around which, embedded in the groove, was wound a .01" diameter steel wire. The two poles of an electromagnet, energised by the voice currents from the microphone, rested against the wire wound round the cylinder. The cylinder remained stationary while the electromagnet rotated around the coil, the wire being magnetised by amounts corresponding to the strength of the voice currents. When the recording was complete the microphone was switched out of circuit and a telephone receiver connected in its place. The electromagnet now returned to the start and on rotating this time the recorded message was heard back.
By the standards then prevailing it worked quite well. Reports by those who heard it remarked on the "naturalness of the reproduction" and the "freedom from noise". These comparisons were of course based on the quality of acoustically recorded Phonograph cylinders of the period.
Patents were taken out throughout the world and Poulsen continued to improve the Telegraphone along with an associate Peder Olaf Pedersen, also an excellent engineer. The next development was a reel-to-reel machine using steel wire passing over a static recording head at 7ft per minute.
In 1903 the American Telegraph Company was incorporated with a capital of $5,000,000, the intention being to manufacture Telegraphones as office dictation machines and telephone recorders. Despite the fact that the Telegraphone had a number of advantages over the wax cylinder Dictaphone - better quality, longer playing time, reuse of the media - the company eventually went into receivership. This was probably due more to bad business practice and scandal surrounding the president of the company than to the limitations of the Telegraphone - the low sound output, length of rewind time before replay possible and the wire often tangling.
Another of Poulsen's devices may be said to be the original version of the hard disk. It consisted of a 4.5 inch diameter steel disk with a raised spiral on the surface which was traced by the electromagnet as the disk rotated.
Poulsen is also known for his work in improving wireless transmission. In 1903 he developed an arc transmitter which increased the frequency range of Duddell's Singing Arc (1900) from 10kHz to 100 kHz, enabling speech to be transmitted up to a radius of 150 miles. By 1920 the Poulsen Arc transmitter was as powerful as 1000kW with ranges of up to 2,500 miles.
Although he never graduated from university we was well acclaimed by his fellow inventors and scientists. He held the Gold Medal of the Royal Danish Society of Science, the Danish Government Medal of Merit, was a Fellow of the Danish Academy of Technical Science, a Fellow of the Swedish Institute for Engineering Research, and an Honorary Doctor of the University of Leipzig.
That the idea of recording sound magnetically was Poulsen's alone is proven by the fact that nobody else has ever claimed credit for the invention, unlike the situation surrounding most other electrical devices such as the telephone, phonograph, cinema, sound-on-film and television.
Wire recording, tape recording, hard disk, floppy disk, credit cards and train tickets - Poulsen had them all covered as shown in the following extract from his 1899, UK Patent No 8961.
Instead of a cylinder with a helical steel wire there may be uses as a receiving device a steel band, supported if necessary on an insulating material and brought under the action of an electromagnet. Such an arrangement has the advantage that a steel band of an desired length may be used. Instead of a cylinder there may be used a disk of magnetisable material over which the electromagnet may be conducted spirally; or a sheet or strip of some insulating material such as paper may be cover with a magnetisable metallic dust and may be used as the magnetisable surface. With the aid of such a strip which may be folded, a message received at any place provided with the new apparatus may be sent to another place where it may be repeated by passing the strip through the apparatus at that place.
He died in 1942.
In 1928, a German engineer, Fritz Pfleumer, demonstrated, to journalists in Berlin, a magnetic recorder of his own design which used paper tape coated with steel dust. He was granted a German patent for his invention. In 1932 AEG took up his idea and began manufacture of the machine calling is the Magnetophon while (what was to later become) BASF produced the tape. In 1936 the German National Court declared that Pfleumer's patent was nul and void because his idea of coating paper tape with iron dust was covered in Poulsen's original patents of 1898 and 1899 - further proof that Valdemar Poulsen stands alone as the inventor of all magnetic recording.
BOB ALLEN
