Plasma speaker

Plasma speakers or ionophones are a form of loudspeaker which varies air pressure via a high-energy electrical plasma instead of a solid diaphragm. Connected to the output of an audio amplifier, plasma speakers vary the size of a plasma glow discharge, corona discharge or electric arc which then acts as a massless radiating element, creating the compression waves in air that listeners perceive as sound. The technique is an evolution of William Duddell's "singing arc" of 1900, and an innovation related to ion thruster spacecraft propulsion.

The term ionophone can also be used to describe a transducer for converting acoustic vibrations in plasma into an electrical signal.

The effect takes advantage of two unique principles: Firstly, ionization of gases causes their electrical resistance to drop significantly, making them extremely efficient conductors, which allows them to vibrate sympathetically with magnetic fields. Secondly, the involved plasma, itself a field of ions, has a relatively negligible mass. Thus as current frequency varies, more-resistant air remains mechanically coupled with and is driven by vibration of the more conductive and essentially massless plasma, radiating a potentially ideal reproduction of the sound source.

Conventional loudspeaker transducer designs use input electrical frequencies to vibrate a significant mass: This driver is coupled to a stiff speaker cone — a diaphragm which pushes air at respective frequencies. But the inertia inherent in its mass resists acceleration — and all changes in cone position. Additionally, speaker cones will eventually suffer tensile fatigue from the repeated shaking of sonic vibration.

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