Valdemar Poulsen

The Danish inventor and engineer Valdemar Poulsen is largely unknown amongst the general public, yet his invention of the telegraphone – telegrafoon in Danish – has laid the foundation of today’s recording industry. This makes him the founding father of the audio cassette, the CD and DVD, the computer disk and diskette, the credit card, the iPod and every other piece of equipment today that records sound or data.

Poulsen was born on November 23, 1869, in Copenhagen, Denmark, as the son of a judge in the Danish High Court. At school he was more interested in physics and drawing than mathematics. Despite his technical interests, his father wanted him to become a medical doctor, so he enrolled at the University of Copenhagen to study medicine. As this was largely unsuccessful he dropped out of university after four years and in 1893 he joined the Copenhagen Telephone Company as a technician.

There he became interested in the magnetic recording of sound. He used a steel piano-wire which he stretched between two walls at a slight angle so an electromagnet could slide down the wire at a uniform speed. To record the sound, the electromagnet was connected to a battery operated microphone while the electromagnet slid downwards. To replay the sound, the battery and microphone were replaced by a telephone’s earpiece and the electromagnet was replaced at the top of the wire again and let go. Remarkably, the experiment worked.

Poulsen had proven that sound could be recorded magnetically and set to work on a machine incorporating his invention. In 1898 he registered a patent in Denmark for his new machine which he called a telegraphone. His first telegraphone consisted of a spirally grooved cylinder around which was wound a thin (.01ӯ) steel wire in its groove. When recording the sound the cylinder would be stationary while the electromagnet connected to a microphone rotated around the drum. To replay the sound the microphone was replaced with a telephone earpiece and the cylinder was rotated. It was an ingenious piece of equipment at that time and those who heard it commented on the "naturalness of the reproduction".

Following his success, Poulsen resigned from the Copenhagen Telephone Company to concentrate on his inventions and to improve his telegraphone for which he had registered patents in many countries. One of his patents read: "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 a 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 covered 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."

Reading this phrase carefully, it is clear that even recording information on a computer disk or a magnetic strip on a credit card was already covered by Poulsen. He even came up with a device consisting of a 4.5’ diameter steel disk with a raised spiral on the surface which was traced by the electromagnet as the disk rotated. It could be said to be the forerunner of today’s computer hard disk.
His next version was a more effective reel-to-reel machine with a static recording head which passed the steel wire at a speed of 7ft/min. The machine could record about 30 minutes of speech.

In 1900 Poulsen demonstrated his telegraphone at the World Exposition in Paris where he managed to record the voice of Emperor Franz Joseph of Austria. This recording still exists and is the oldest magnetic sound recording surviving today. His invention created considerable interest and he was awarded a Grand Prix for his machine. Despite this success he battled to find sufficient financial backing for the manufacture and sale of his machines.

One of his other inventions was the Arc Transmitter, developed in 1903, which enabled speech to be transmitted up to a radius of 150 miles. By 1920 the Poulsen Arc transmitter had a range of up to 2,500 miles – a great improvement in wireless radio and telegraphy. This technology was widely adopted by the US Navy.

One of the ways Denmark has honoured its great son, was a postage stamp commemorating the centenary of his birth. The stamp does not feature his portrait (he’s not portrayed on any stamp) but shows a stylized representation of his famous telegraphone.

Poulsen died in July 1942 in Copenhagen, Denmark.

From steel wire to magnetic tape to magnetic disk

In 1927, the American inventor J.A. O'Neill replaced Poulsen’s steel wire with a magnetically coated ribbon resulting in the magnetic tape recorders we know today. They’ve been used for audio recording and (in computers) for the recording of information.

                                                                                                                                    computer tape deck

In the early days of computers magnetic tape has been used to record information which was formerly held in punched cards and perforated paper tape. Together with magnetic tape the magnetic disk was used for the same purpose.

When the mini and micro computers arrived in the seventies, one would often use audio cassette tapes to store programs and data for these small machines. This was well-proven technology and one could even send the little cassettes by mail using a special envelope like this cassette mailer from Egypt.


When in the eighties the Personal Computer arrived on the scene, technology had advanced from tape cassette to floppy disk and stiffy disk for the digital storing of information.

In 1982 the Compact Disk (CD) came to the market and took over from the floppy/stiffy disk. A CD, which is read by a laser, can hold 700 Mb of data which surpasses the much more limited capacity of the older stiffy disk. Similar digital recording technology is used in DVDs, memory sticks (or USB-sticks) or the memory card in your digital camera.

Over the past few decades, digital recording has all but completely supplanted analog recording, i.e. magnetic recording has become virtually outdated technology. But it was Valdemar Poulsen who showed us the way.

© Wobbe Vegter, 2007

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