The Singing Arc

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William Du Bois Duddell and the "Singing Arc"(1899)

William Du Bois DuddellBefore Thomas Alva Edison invented the electric light bulb electric street lighting was in wide use in Europe. A carbon arc lamp provided light by creating a spark between two carbon nodes. The problem with this method of lighting, apart from the dullness of the light and inneficient use of electricity was a constant humming noise from the arc.

The British physicist William Duddell was appointed to solve the problem in London in 1899 and during his experiments found that by varying the voltage supplied to the lamps he could create controllable audible frequencies

By attaching a keyboard to the arc lamps he created one of the first electronic instruments and the first electronic instrument that was audible without using the telephone system as an amplifier/speaker.

When Duddell exhibited his invention to the London institution of Electrical Engineers it was noticed that arc lamps on the same circuit in other buildings also played music from Duddell's machine this generated speculation that music deliverd over the lighting network could be created.

Duddell didn't capitalise on his discovery and didn't even file a patent for his instrument.

William Du Bois Duddell and the 'Singing Arc' (1899) carbon arc lamp
A carbon arc streetlamp of the type used in Victorian Britain

Prior to the invention of the incandescent light bulb, Arc lamps were used to light the streets. They created light using an electrical arc between two carbon electrodes. These lamps often produced audible humming, hissing, or even howling sounds. In 1899 Duddell, a student of William Ayrton at London Central Technical College, was asked by Ayrton to look into this problem. The sounds were created by instabilities in the current caused by the arc's negative resistance.
Singing Arc Schematics
Duddell connected a tuned circuit consisting of an inductor and capacitor across an Arc.

The negative resistance of the arc excited audio frequency oscillations in the tuned circuit at its resonant frequency, which could be heard as a musical tone coming from the arc. Duddell used his oscillograph to determine the precise conditions required to produce oscillations.

Singing ArcTo demonstrate his invention before the London Institution of Electrical Engineers, he wired a keyboard to produce different tones from the arc, and used it to play a tune, God Save the Queen making it one of the first examples of electronic music.

This device, which became known as the "singing arc", was one of the first electronic oscillators.

Duddell toured the country with his invention which unfortunately never became more than a novelty. It was later recognised that if an antena was attached to the singing arc and made to 'sing' at radio frequencies rather than audio it could be used a continuous radio wave transmitter. The carbon arc lamp's audio capabilities was also used by Thadeus Cahill during his public demonstrations of his Telharmonium ten years later.

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