The singing Tesla coil, sometimes called a zeusaphone, thoramin or musical lightning, is a form of plasma speaker. It is a variation of a solid state Tesla coil that has been modified to produce musical tones by modulating its spark output. The resulting pitch is a low fidelity square wave like sound reminiscent of an analog synthesizer. The high-frequency signal acts in effect as a carrier wave; its frequency is significantly above human-audible sound frequencies, so that digital modulation can reproduce a recognizable pitch. The musical tone results directly from the passage of the spark through the air. The flexibility of the sound is limited by the fact that the solid-state coil produces square rather than sinusoidal waves; but simple chords are possible.
The term "singing Tesla coil" was coined by David Nunez, the coordinator of the Austin, Texas chapter of Dorkbot, while describing a musical Tesla coil presentation by Joe DiPrima and Oliver Greaves during DorkBot's 2007 SXSW event. The term was then made popular by a CNET article describing the event.
They had been doing public performances with the technology since March 2006. Shortly after that, DiPrima named their performance group "ArcAttack" and became the first musical group to ever use this technology in live performance.
While early versions of musical Tesla coils generally used zero crossing threshold detectors as a method of producing music through their spark output, Scott Coppersmith was the first person to design a complete MIDI-based Tesla coil system.
MIDI is the most common method of music production. It works by means of a microcontroller that is programmed to interpret MIDI data, and output a corresponding Pulse-width modulation (PWM) signal. This PWM signal is coupled to the Tesla coil through a fiber optic cable, and controls when the Tesla coil turns on and off. [Wikipedia].