Why are Sound Labs Full-range Electrostatic speakers so big?
Good question. First, electrostatic forces are weaker than magnetic forces. Therefore, membrane excursions are limited. Since acoustic energy is a function of the volume of air that is displaced by the membrane, limited linear displacement is compensated for by making the membrane area larger. However, this has a beneficial effect: the large membrane exhibits a more resistive coupling to the air. This means less energy is thrown off the sides in the form of eddy currents, which in turn reduces the reflected energy coming off of the side walls, which in turn improves imaging. To produce a given loudness level, the speaker size must become larger as the low-frequency cut-off is lowered. Therefore, truly full-range dipole speakers must be larger than box speakers. The problem would be solved if the electrostatic panel was mounted in a wall or a large open baffle.
