Alan Blumlein

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Alan Dower Blumlein
Born	29 June 1903 Hampstead, London
Died	7 June 1942 (aged 38) Welsh Bicknor, Herefordshire
Education	Imperial College London
Spouse(s)	Doreen Lane
Children	Simon Blumlein David Blumlein
Parents	Semmy Blumlein Jessie Dower
Work
Employer(s)	EMI
Significant projects	H2S radar
Significant design	Ultra–Linear amplifier
Significant advance	Stereophonic sound Television

Alan Dower Blumlein (29 June 1903 – 7 June 1942) was an English electronicsengineer, notable for his many inventions in telecommunications, sound recording, stereo,television and radar. He received 128 patents and was considered as one of the most significant engineers and inventors of his time.^[1][2]

He died during World War II on 7 June 1942, aged 38, during the secret trial of an H2S airborne radar system then under development, when all on board the Halifax bomber he was flying in were killed when it crashed at Welsh Bicknor in Herefordshire.^[2]

[edit]
Alan Dower Blumlein was born on 29 June 1903 in Hampstead, London to Semmy Blumlein, a German-born naturalised British subject of Jewish descent,^{[Note 1]} and Jessie Dower, a Scottish missionary's daughter. He was christened as a Presbyterian, though he later married in a Church of England parish. His future career seems to have been determined by the age of seven, when he presented his father with an invoice for repairing the doorbell, signed "Alan Blumlein, Electrical Engineer" (with "paid" scrawled in pencil). His sister claimed that he could not read proficiently until he was 12. He replied "no, but I knew a lot of quadratic equations!"Early life

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.

In mid-1930, Blumlein met Doreen Lane, a Preparatory school teacher five years his junior. After two-and-a-half years of courtship the two were married in 1933. Lane was warned by acquaintances before the wedding that, "There was a joke amongst some of his friends, they used to call it 'Blumlein-itis' or 'First Class Mind'. It seems that he didn't want to know anyone who didn't have a first class mind." Recording engineer, J.B. Kaye, who was Blumelin's closest friend and best man at the wedding,^[3] thought the couple were well matched.^[4]

[edit]Career and inventions

[edit]Telecommunications

In 1924 Blumlein started his first job at International Western Electric, a division of the Western Electric Company. The company subsequently became International Standard Electric Corporation and then, later on, 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 weightingnetworks.

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

In 1925 and 1926, Blumlein and John Percy Johns designed an improved form of loading coil which reduced loss and 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.

[edit]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 headthen used, and on which substantial royalties had to be paid. He invented the moving-coil disc cutting head, which not only got around the patent but 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 1 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.

[edit]Ultra-linear amplifier

In June 1937, Blumlein patented one of his most important audio inventions, the Ultra-Linear amplifier (Patent 496,883, dated 5 June 1937). A deceptively simple design, the circuit provided a tap on the primary winding of the output transformer to provide feedback to the second grid, which improved the amplifier's linearity. With the tap placed at the anode end of the primary winding, the tube (valve) could be connected as a triode, and if the tap was at the supply end, it could be connected as a pure pentode. Blumlein discovered that if the tap was placed at a distance 15-20% down from the supply end of the output transformer, the tube or valve would combine the positive features of both the triode and the pentode design.

[edit]Stereophonic sound

In 1931, Blumlein developed what he called "binaural sound", now known as stereophonic sound (stereo).^[5]

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 Isaac Shoenberg in the late summer of 1931. His earliest notes on the subject are dated 25 September 1931, and his patent had the title "Improvements in and relating to Sound-transmission, Sound-recording and Sound-reproducing Systems". The application was dated 14 December 1931, and was accepted on 14 June 1933 as UKpatent number 394,325.^[6]

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 stereo headphones instead of a pair of loudspeakers;
• 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 fully realised.

[edit]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 research.

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.
• The slot antenna. (515684, filed 7 March 1939.)

Blumlein was also largely responsible for the development of the waveform structure used in the 405-line Marconi-EMI system - developed for the UK's BBC Television Service at Alexandra Palace, the world's first scheduled "high definition" (240 lines or better) television service - which was later adopted as the CCIR System A.