Plasma speaker

The technique is a much later development of physics principles demonstrated by William Duddell's "singing arc" of 1900,[2] and Hermann Theodor Simon published the same phenomenon in 1898.

[3] The term ionophone was used by Dr. Siegfried Klein who developed a plasma tweeter that was licensed for commercial production by DuKane with the Ionovac and Fane Acoustics with the Ionofane in the late 1940s and 1950s.

[4] The effect takes advantage of several physical principles:[5] First, ionization of a gas creates a highly conductive plasma, which responds to alternating electric and magnetic fields.

Thus, the air remains mechanically coupled with the essentially massless plasma, allowing it to radiate a nearly ideal reproduction of the sound source when the electric or magnetic field is modulated with the audio signal.

The ExcelPhysics variant used a flyback transformer to step up voltage, a 555 timing chip to provide modulation and a 44 kHz carrier signal, and an audio amplifier.

A similar effect is occasionally observed in the vicinity of high-power amplitude-modulated radio transmitters when a corona discharge (inadvertently) occurs from the transmitting antenna, where voltages in the tens of thousands volts are involved.

Due to the destructive effects of the (self-sustaining) discharge this cannot be permitted to persist, and automatic systems momentarily shut down transmission within a few seconds to quench the "flame".