A history on plasma loudspeakers
In 1951 Siegfried Klein of Paris produced the "Ionophone" which unlike any other practical loudspeaker to date, had no mechanical moving parts. It used a small quartz tube which included a Kanthal electrode. When connected to a radio frequency oscillator of high voltage it caused ionic discharge to take place in the air within the quartz tube. Resultant pressure waves through the throat of a horn translate into sound waves. This venture failed although the unit was produced for a short time in the USA. In the 1960's a redesign by Mr. Faulkus was produced as the IonoFone but production discontinued about 1968."