Abstract This paper is focused on a hermetically sealed cavity which can be electrostatically excited and driven as a loudspeaker. The actuation principle is based on a diaphragm that is rolling against the cavity bottom to reach both large displacements and strong electrostatic forces. The loudspeaker is primarly intended for airborne ultrasound. Test speakers have been manufactured by micromachining in silicon using anisotropic and isotropic etching, and wafer bonding. Experiment shows an acoustic output of 112 dB in sound pressure level at the resonance frequency of 127 kHz, measured at a distance of 10 mm with 50 V peak-to-peak in applied driving voltage. An empirical Q -value of 7 is found. Measurements indicate that the resonance frequency of the loudspeaker can be tuned with an applied biasing voltage.