X-Nico

Plasma speaker

The technique is an evolution of William Duddell's "singing arc" of 1900, and an innovation related to ion thruster spacecraft propulsion.

William Duddell

However, Danish physicists Valdemar Poulsen and P. O. Pederson were able to increase the frequency of Duddell's oscillator to the radio range, and in 1902 patented the Poulsen arc radio transmitter, the first transmitter which could generate continuous waves.

see also