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Electrophones: A Quick Historical Survey

Electricity has been used in connection with musical instruments since the 18th century. One example is the Clavecin électrique, described by Jean-Baptiste de Laborde in 1761, a carillon electrically controled from a keyboard. Here, in fact, the electrical element is not directly related to sound production, but as a means of control only. Other instance is the Musical Telegraph, invented by Elisha Gray in 1876.

Rather than instruments really useful for musical purposes, many early instances of instruments involving the use of electricity mainly scientific curiosities. However, in the last years of the 19th century, Thaddeus Cahill conceived an instrument with real musical potential, called Dynamopnone or Telharmonium. An instrument of huge dimensions (one of the versions was 18 m long, weighing around 200 tons), its keyboards controlled electric circuits which, for each note, mixed very strong electrical alternate currents, with frequencies corresponding to harmonics 1-6 of that note. Such currents were generated or controlled by rotating dented wheels or electrical alternators (generators), set to rotate at carefully controlled speeds, in order to produce the intended frequencies. When mixed in due proportions, such currents would have different waveforms, corresponding to different timbres. The instrument was thus supposed to synthesize the sounds of different instruments.

The Telharmonium didn't directly produce sounds. Instead, it created electrical currents representing the intended sounds, which could be heard by applying these currents to what was then known as a telephone receiver. In fact, Cahill's idea was to create a service whereby music was distributed to subscribers by means of telephone lines, something which he put into practice, although with a short-lived success. Long term faillure resulted from of the instrument's huge size, the amount of electrical energy necessary to put it into motion, and interferences of the very strong currents that needed to cross the (dedicated) telephone lines, which interfered with the audio signals in the regular telephone lines.

Such strong currents were necessary because at that time there was no practical way to amplify an electrical signal. But in the 1930's such resources were readily available, and by that time a number of other instruments used a similar process of rotating wheels (tone wheels) which controlled (now much weaker) electrical currents at the rates necessary to produce a number of partials for each note. The most successful of these instruments was the Hammond Organ, but the same principle was used in the Coralcello.

Amplification by electronic means had been made possible thanks to a thermionic valve (or vacuum tube) patented in 1907 by Lee De Forest. This valve would later be known as as triode (because it has three electrodes) and was a development of De Forest's . Another use of these valves, found around 1915, was to create electronic oscillators, which would be the basis of De Forest's own Audion Piano (a very unstable instrument which never really worked properly) and René Bertrand's Dynaphone. This later instrument, about which very little information subsists, is important because around 1928 Edgard Varèse's was very much interested in its potential for creating new sounds for composers to explore and for research purposes. Apparently, it was an electronic audio oscillator controlled from a large, rotating dial.

A more successful way of using valve-controlled electronic oscillator was used in Lev Termen's Thereminvox, or Theremin, and Maurice Martenot's Ondes Musicales, or Ondes Martenot. In both cases the oscillators produce inaudible, high-frequency oscillators: around 80,000&nbs;Hz for the Theremin and 150,000&nbs;Hz for the Ondes. Each instrument has a pair of oscillators, one with a fixed frequency, the other with a variable one, and it is the interference between these two oscillators (the difference tone they produce) that is transformed into sound by a loudpeaker. The frequency of the variable oscillator is produced by different means in both instruments:

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