Looking Into a Plasma Loudspeaker

A 325-kHz atmospheric discharge can be modulated at audio frequencies so that it acts as a loudspeaker by direct electroacoustic coupling, without any electromechanical components. In exploring the details of the mechanism, it has been useful to visualize the heated gas within and around the discharge plume using Schlieren techniques. This has enabled a 2-D reconstruction of the translational temperature of the neutral gas (up to 2500 K) that complements spectroscopic measurements of rotational and vibrational temperatures (up to 2700 K) in the luminous region.