Plasma speakers, also known as ionophores, are a type of loudspeaker which modifies air pressure with a high-energy electrical plasma. When connected to the output of an audio amp, the plasma speakers change the size of the electric arc, the plasma glow discharge, or the corona discharge. Eventually, they operate as a massless radiating element. This process creates the compression waves that the human ear is able to perceive as a sound. It’s worth mentioning that that tweeters made of plasma arcs have no resonance nor transient conflicts.
Speakers use a variety of materials within their construction. The lighter the material, the faster the response. Also, lighter materials tend to produce better transients and plasma arcs have no weight at all. The speaker operates by modifying the temperature and moving the airflow.
Plasma arc speakers were invented by William Duddeles at the beginning of the 1900s, as an evolution of Singing Arc and an innovation related to ion thruster spacecraft propulsion. The invention of the ionophore emerged when its creator discovered that by varying the voltage of the arc, the sound generated also changed. Decades later, Siegfried Klein tuned the arc speaker by inserting the arc in a quartz tube. He then got the idea of connecting this device to a horn, therefor creating both a speaker and a microphone. Years later, DuKane Corporation manufactured the air-ionizing Ionovac. Nowadays, this design is still in use and easily available to the public.
The first designs of the plasma speaker ionized the surrounding air through both nitrogen and oxygen. It’s worth mentioning that in an intense electrical field, both oxygen and nitrogen are able to generate a reaction. In closed spaces, they can be quite dangerous.
There have been several varieties of plasma speakers. Plasmatronics manufactured a commercial plasma speaker that involved a helium tank in order to ionize the gas. Years later, the Air Force Weapons Laboratory designed a commercial helium-plasma tweeter known as the Plasmatronics Hill Type I. This device avoided the nitrogen and ozone oxides that were produced by the radio radiofrequency decomposition of the air. The design of the Plasmatronics Hill Type I depended on a quieter glow discharge mode. These speakers need a constant supply of helium.
ExcelPhysics and Image Scientific Instruments provide their own version of plasma speakers, making them more affordable and available to the public. The design created by ExcelPhysics uses a flyback transformer that helps elevate the voltage. It also includes an audio amp, a 555 timing chip to achieve the accurate modulation, and a 4Hz carrier signal.