Abstract: A transducer assembly for converting electrical energy into acoustical energy and vice versa in which a single multi-layer piezoelectric transducer drives (or is driven) a flat diaphragm secured at its edges in a housing. The piezoelectric transducer is a multi-layer wafer which is secured to a flexible sheet which in turn is secured over an aperture in the diaphragm. The piezoelectric multi-layer wafer has its central portion constrained from movement which increases its edgewise movement to twice its unconstrained value. The movement constraint is provided by a post on the housing which is cemented to a central aperture in the wafer. It has been found that there is a maximum ratio of the post diameter to the wafer diameter for optimum performance of the speaker.