Thaddeus Cahill (1867–1934) was an American inventor who completed one of the most ambitious electronic music projects ever created. The advanced design of his hard-wired instrument came fifteen years before vacuum tube availability, and his unique idea of selling live electronic music over a telephone network foreshadowed Muzak, radio broadcasting and cable TV concepts decades earlier. Cahill was the first man to foresee the commercial use of electronic music, and also had the means and persistence to make his dreams come true. He built the first electronic music synthesizer with several effects and the ability to shape the sound, used a polyphonic keyboard with touch-sensitive (dynamic) keys. He improved the sound-generating technique of the rotating tone wheel, what Laurens Hammond (1895–1973) used later in his famous electronic organ. Also he broadcasted his electronic music via telephone wires.
Cahill obtained a patent in 1896. His instrument became known under two different names: Dynamophone and Telharmonium. It consisted of electrical tone-generating devices, dynamics control devices for building and shaping individual tones, a keyboard for activating the tone-generating circuits, and a speaker.
The complexity of Cahill's musical invention is surprising. The sound generating mechanism consisted of twelve "pitch rollers" or axles with a series of "rheotomes" or cogged metal tone wheels mounted on them. Turning the pitch rollers made the tone wheels rotate quickly to bring each wheel into contact with a metal brush that was part of an electrical circuit. The on-and-off contact between the grooves in a tone wheel and a brush produced an electrical oscillations of a certain frequency.
Each of the twelve pitch rollers corresponded to one note of the chromatic scale. All of them were rotated simultaneously by a single motor using a complicated wheel and belt system, keeping the rotation speed constant and all the rollers rotating at a constant rate. This way all the pitch rollers would remain in line with each other.
Each of the tone wheels produced a single pure sine tone and harmonics were created by using additional tone wheels, each one for different harmonic component of the corresponding fundamental frequency. So that each note had overtones provided by five additional tone wheels.
The first five octaves used six harmonics, the sixth four and the seventh only two. This resulted from the fact that the higher frequency sounds consist of fewer overtones. The original Telharmonium instrument had 84 notes corresponding to the 84 notes of a seven-octave piano. These notes used 408 individual tone wheels to get all the necessary harmonics.
Each group of tone wheels corresponding to one note of the scale was connected to an individual key with an electrical circuit. Key was pressed to close the circuit and then produce a note. The keys were finger pressure sensitive thanks to the use of a coil in the closing process. When a key was pressed harder, the closer it got to the coil and the louder the sound was.
The tones being played were first combined in a "mixer", in which it was possible to control and balance the individual components of the whole sound. By shaping the sound through mixing and filtering, the Telharmonium could be used to synthesize the timbres of orchestral instruments. The sound was then routed through regular telephone wires to telephone headsets equipped with large paper tubes for sound projection. Cahill's patent covered also the design of a speaker with wooden soundboard – a unique prototype of the modern speakers.