James Green's Research Pages

Plasma Speaker

This project involves the design of a Class D audio amplifier in the form of a flyback converter. The objective is to form a short (50 mm - 75 mm) arc (plasma) in air between two tungsten electrodes and to modulate the current flowing in accordance with some program material (music etc.). This modulation of current causes heating and cooling of the air surrounding the plasma. The heating and cooling of the air causes expansion and contraction of the air which is perceived as sound.

This kind of speaker has some key advantages including "zero moving mass" which yields very wide bandwidth and no magnetic components (which are sometimes accused of introducing non-linearities). Nevertheless plasma speakers have many defects which have prevented their wide acceptance as an electro-acoustic transducer including the exposed EHT parts, the generation of a (vanishingly) small amount of ozone and their lack of "good bass". The example below due to timetec shows the lack of bass and is an excellent example of a plasma speaker. It is possible to increase the volume of air moved (and in so doing improve the bass response) by making the plasma a different shape (a cylinder may be good), however ensuring the stability of more complex shapes can be tricky. The principle difficulty is that the hot air surrounding the plasma rises and draws new air from below, this flow is often turbulent and acts to disrupt the plasma. One option is to guide the plasma using magnetic fields, another is to provide dedicated structures to ensure reasonably lamina air flow (think about how a Bunsen burner works).