Acoustic characteristics and Distortion of an Ionic Loudspeaker

This paper presents some acoustic characteristics of a positive-corona-discharge loudspeaker, based on a parallel array of wires (corona electrode) and bars (collector electrode). The acoustic pressure is a combination of a monopolar and a dipolar term. The former arises from heat exchange in the wire surroundings and the latter stems from elastic collisions of drifting ions and neutral molecules in the gap between the electrodes. The relative contribution of both terms is studied. A differential circuit is devised to measure the AC ionic current in real time. This allows to relate it to the acoustic pressure and to compute the loudspeaker efficiency. Measurements on directivity and frequency response evidence that, even though the loudspeaker is a sum of discrete sources, it behaves as a rectangular diaphragm. This reduces the acoustical short-circuit and improves the transducer efficiency. Finally this work proposes a simple method to decrease the sound pressure harmonic distortion by applying a simple linearizing algorithm (based on the I-V discharge relationship) to the input signal.