The ‘Audion Piano’ and Audio Oscillator. Lee De Forest. USA, 1915

 “Audion Bulbs as Producers of Pure Musical Tones” from 'The Electrical Experimenter' December 1915
“Audion Bulbs as Producers of Pure Musical Tones” from ‘The Electrical Experimenter’ December 1915

Lee De Forest , The self styled “Father Of Radio”  (the title of his 1950 autobiography) inventor and holder of over 300 patents, invented the triode electronic valve or ‘Audion valve’ in 1906- a much more sensitive development of John A. Fleming’s diode valve.

The immediate application of De Forest’s triode valve was in the emerging radio technology of which De Forest was a tenacious promoter. De Forest also discovered that the valve was capable of creating audible sounds using the heterodyning or beat frequency technique: a way of creating audible sounds by combining two high frequency signals to create a composite lower frequency within audible range – a technique that was used by Leon Termen in his Theremin and Maurice Martenot in the Ondes Martenot some years later. In doing so, De Forest inadvertently invented the first true audio oscillator and paved the way for future electronic instruments and music.

Lee De Forest's Triode Valve of 1906
Lee De Forest’s Triode Valve of 1906

In 1915 De Forest used the discovery of the heterodyning effect in an experimental instrument that he christened the ‘Audion Piano’ . This instrument – based on previous experiments as early as 1907 – was the first vacuum tube instrument and established the blueprint for most future electronic instruments until the emergence of transistor technology some fifty year later.

The Audion Piano, controlled by a single keyboard manual, used a single triode valve per octave, controlled by a set of keys allowing one monophonic note to be played per octave. This audio signal could be processed by a series of capacitors and resistors to produce variable and complex timbres and the output of the instrument could be sent to a set of speakers placed around a room giving the sound a novel spatial effect. De Forest planned a later version of the instrument that would have separate valves per key allowing full polyphony- it is not known if this instrument was ever constructed.

De Forest described the Audio Piano as capable of producing:

“Sounds resembling a violin, Cello, Woodwind, muted brass and other sounds resembling nothing ever heard from an orchestra or by the human ear up to that time – of the sort now often heard in nerve racking maniacal cacophonies of a lunatic swing band. Such tones led me to dub my new instrument the ‘Squawk-a-phone’….The Pitch of the notes is very easily regulated by changing the capacity or the inductance in the circuits, which can be easily effected by a sliding contact or simply by turning the knob of a condenser. In fact, the pitch of the notes can be changed by merely putting the finger on certain parts of the circuit. In this way very weird and beautiful effects can easily be obtained.”
(Lee De Forest’s Autobiography “The Father Of Radio”)

And From a 1915 news story on a concert held for the National Electric Light Association

“Not only does de Forest detect with the Audion musical sounds silently sent by wireless from great distances,but he creates the music of a flute, a violin or the singing of a bird by pressing button. The tune quality and the intensity are regulated by the resistors and by induction coils…You have doubtless heard the peculiar, plaintive notes of the Hawaiian ukulele, produced by the players sliding their fingers along the strings after they have been put in vibration. Now, this same effect,which can be weirdly pleasing when skilfully made, can he obtained with the musical Audion.”

Advert for De Forest wireless equipment
Advert for De Forest wireless equipment

De Forest, the tireless promoter, demonstrated his electronic instrument around the New York area at public events alongside fund raising spectacles of his radio technology. These events were often criticised and ridiculed by his peers and led to a famous trial where De Forest was accused of misleading the public for his own ends:

“De Forest has said in many newspapers and over his signature that it would be possible to transmit human voice across the Atlantic before many years. Based on these absurd and deliberately misleading statements, the misguided public … has been persuaded to purchase stock in his company. “
Lee De Forest, August 26, 1873, Council Bluffs, Iowa. Died June 30, 1961
Lee De Forest, August 26, 1873, Council Bluffs, Iowa. Died June 30, 1961

De Forest collaborated with a sceptical Thadeus Cahill in broadcasting early concerts of the Telharmonium using his radio transmitters (1907). Cahill’s insistence on using the telephone wire network to broadcast his electronic music was a major factor in the demise of the Telharmonium. Vacuum tube technology was to dominate electronic instrument design until the invention of transistors in the 1960’s. The Triode amplifier also freed electronic instruments from having to use the telephone system as a means of amplifying the signal.


Lee De Forest “Father Of Radio” (Autobiography).

Wireless: From Marconi’s Black-Box to the Audion (Transformations: Studies in the History of Science and Technology) 2001 author(s) Sungook Hong

Lee de Forest: King of Radio, Television, and Film 2012. Mike Adams (auth.).

Theremin: Ether Music and Espionage. By Albert Glinsky

Electronic Music. Nicholas Collins, Margaret Schedel, Scott Wilson

Media Parasites in the Early Avant-Garde: On the Abuse of Technology and Communication. Arndt Niebisch 2012

Electric Relays: Principles and Applications. Vladimir Gurevich

5 thoughts on “The ‘Audion Piano’ and Audio Oscillator. Lee De Forest. USA, 1915”

  1. FYI: The transistor was invented in 1947. Transistor equipment gained in practicality and commercial potential through the ’50’s (for example an all-transistor car radio was introduced in 1955) and by the 60’s it was much more commercially viable (as compared to vacuum tube equipment) than before.

    Your statement “Vacuum tube technology was to dominate electronic instrument design until the invention of transistors in the 1960′s” is substantially true except I’d suggest “widespread commercial viability” instead of “invention.”

    Love your site! Thanks for the cool retro gizmos!

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