A transducer assembly has a generally planar resonator (12) (such as a disc) bonded on one face to a sheet of piezoelectric material (12B) and having a mounting flange (12C) (which may extend all around the periphery of the resonator) to mount the resonator between inner (13) and outer (11) mounting elements such as rings. An electric circuit (24) drives the piezoelectric sheet (12B) and, when used for sound generation, a tuned acoustic structure is provided for directing sound away from the resonator (12).