Alan Blumlein

Alan Dower Blumlein was an electronics engineer who made a great many inventions in telecommunications, sound recording, stereo, television and radar. He received 128 patents.

File:Alan Blumlein.jpg

Front cover of Blumlein biography

Introduction

Alan Dower Blumlein was born on June 29, 1903 in Hampstead, London. His future career seems to have been determined by the age of seven, when he presented his mother with an invoice for repairing the doorbell, signed "Alan Blumlein, Electrical Engineer".

After matriculating at Highgate School in 1921, he studied at City and Guilds College (part of Imperial College). He won a Governor's scholarship and joined the second year of the course. He graduated with a first class honours B.Sc two years later.

He died on June 7, 1942, during a trial of airborne radar, when the Halifax bomber he was flying in crashed, killing everyone on board.

Career and inventions

Telecommunications

In 1924 Blumlein started his first job at International Western Electric, a division of Bell Labs. The company subsequently became International Standard Electric Corporation and then Standard Telephones and Cables (STC).

During his time there, he measured the amplitude/frequency response of human ears, and used the results to design the first weighting networks.

In 1924 he published (with Professor Edward Mallett) the first of his only two IEE papers, on high-frequency resistance measurement. This won the IEE's 'Premium' award for innovation. The following year he wrote (with Norman Kipping) a series of seven articles for Wireless World.

In 1925 and 1926, Blumlein and John Percy Johns designed an improved form of loading coil which reduced crosstalk in long-distance telephone lines. These were used until the end of the analogue telephony era. The same duo also invented an improved form of AC measurement bridge which became known as the Blumlein Bridge. These two inventions were the basis for Blumlein's first two patents.

His inventions while working at STC resulted in another five patents, which were not awarded until after he left the company in 1929.

Sound recording

In 1929 Blumlein handed in his notice at STC and joined the Columbia Graphophone Company, where he reported directly to general manager Isaac Shoenberg.

His first project was to find a method of disc cutting that circumvented a Bell patent in the Western Electric moving-iron cutting head then used, and on which substantial royalties had to be paid. He invented the moving-coil disc cutting head, which not only got round the patent, it offered greatly improved sound quality. He led a small team which developed the concept into a practical cutter. The other principal team members were Herbert Holman and Henry 'Ham' Clark. Their work resulted in several patents.

Early in 1931, the Columbia Graphophone Company and the Gramophone Company merged and became EMI. New joint research laboratories were set up at Hayes and Blumlein was officially transferred there on 1st November the same year.

During the early 1930s Blumlein and Herbert Holman developed a series of moving-coil microphones, which were used in EMI recording studios and by the BBC at Alexandra Palace.

Stereo

Blumlein developed his ideas on what he called 'binaural sound', now known as stereo, during this same period.

In early 1931, Blumlein and his wife were at a local cinema. The sound reproduction systems of the early 'talkies' invariably only had a single set of speakers - which could lead to the somewhat disconcerting effect of the actor being on one side of the screen whilst his voice appeared to come from the other. Blumlein declared to his wife that he had found a way to make the sound 'follow' the actor across the screen.

The genesis of these ideas is uncertain, but he explained them to Shoenberg in the late summer of 1931. His earliest notes on the subject are dated 25 September 1931, and his patent was applied for on 14 December 1931 ("Improvements in and relating to Sound-transmission, Sound-recording and Sound-reproducing systems", No. 394325).

Whereas work led by Harvey Fletcher at Bell Labs at about the same time considered sound systems using multiple channels, Blumlein always aimed at a system with just two channels.

The patent covered many ideas in stereo, some of which are used today and some not. Some 70 claims include:

A 'shuffling' circuit, which aimed to preserve the directional effect when sound from a spaced pair of microphones was reproduced via a pair of loudspeakers instead of stereo headphones;
The use of a coincident pair of velocity microphones with their axes at right angles to each other, which is still known as a 'Blumlein pair';
Recording two channels in the single groove of a record using the two groove walls at right angles to each other and 45 degrees to the vertical;
A stereo disc-cutting head;
Using hybrid transformers to matrix between left and right signals and sum and difference signals;

Binaural experiments began in early 1933, and the first stereo discs were cut later the same year.

Much of the development work on this system for cinematic use did not reach completion until 1935. In a few short test films (most notably, 'Trains At Hayes Station' and, 'The Walking & Talking Film'), Blumlein's original intent of having the sound 'follow' the actor was realised fully.

Television

Television was developed by many individuals and companies throughout the 1920s and 1930s. Blumlein's contributions, as a member of the EMI team, started in earnest in 1933 when his boss, Isaac Shoenberg, assigned him full-time to TV work.

His ideas included:

Resonant flyback scanning (the use of a tuned circuit in the creation of a sawtooth deflection waveform). (British Patent No. 400976, application filed April 1932.)
Use of constant-impedance network in power supplies to obtain voltage regulation independent of load frequency, extending down to DC (421546, filed 16 June 1933).
Black-level clamping (422914, filed 11 July 1933 by Blumlein, Browne and Hardwick). This is an improved form of DC restoration, compared to the simple DC restorer (consisting of a capacitor, diode and resistor) which had been patented by Peter Willans three months earlier.

Radar

External links

References

Alexander, Robert Charles[1] (1999). The Inventor of Stereo: The Life and Works of Alan Dower Blumlein. Focal Press. ISBN 0240516281.
Burns, Russell W (2000). The Life and Times of A. D. Blumlein. IEE History of Technology series. ISBN 085296773X

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