What are the Plasma speakers?
Plasma speakers or ionophones are a form of a 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. It creates the compression waves in the air that listeners perceive as sound. Tweeters made out of plasma arcs have a major advantage – they have no resonance or transient problems. Most audiophiles know that the lighter the material used in a speaker, the faster the response can be. What’s more, lighter materials produce better transients. Well, plasma arcs have ZERO weight. The plasma speaker works by moving air via changing the temperature in its chamber.
The History of Plasma Arc Speakers
The base for plasma arc speakers, also known as ionophones, was the invention of William Duddeles back in 1900. The technique is an evolution of William Duddell’s “singing arc” of 1900, and an innovation related to ion thruster spacecraft propulsion. William found that by varying the voltage to the arc, it changed the sound that was produced. Much later a fellow by the name of Siegfried Klein got involved and tuned it by putting the arc in a small quartz tube. Coupling this to a horn, he was able to produce a speaker and a microphone. In the 1950s, the pioneering DuKane Corporation produced the air-ionizing Ionovac, marketed in the UK as the Ionophone. Currently, there remain manufacturers in Germany who use this design, as well as a do-it-yourself design available on the Internet.
Early plasma-speaker designs ionized ambient air containing the gases nitrogen and oxygen. Therefore in an intense electrical field, these gases can produce reactive by-products. On the other hand, in closed rooms, they can reach a hazardous level. Plasmatronics produced a commercial plasma speaker that used a helium tank to provide the ionization gas. In 1978 Alan E. Hill of the Air Force Weapons Laboratory in Albuquerque, NM, designed the Plasmatronics Hill Type I, a commercial helium-plasma tweeter. This avoided the ozone and nitrogen oxides produced by the radiofrequency decomposition of air in an earlier generation of plasma tweeters. Their design is the only one relying on the quieter glow discharge mode instead of the more common arc and corona discharges. But the operation of such speakers requires a continuous supply of helium.
To make the plasma speaker a more widely available product, ExcelPhysics, a Seattle-based company, and Images Scientific Instruments, a New York-based company, both offered their own variant of the plasma speaker as a DIY kit. Moreover, the ExcelPhysics variant uses a flyback transformer to step up voltage, a 555 timing chip to provide modulation and a 44 kHz carrier signal, and an audio amplifier.