Abstract: The invention relates to a dual frequency sonar transducer assembly which may be operated at low and/or high frequencies in a sonar array. The assembly comprises a low frequency unit of tonpilz design including a low frequency driver, a low frequency tail mass and a composite head mass, the composite head mass acting as a single low frequency water driving piston and comprising a plurality of high frequency units forming individual high frequency water driving pistons. The high frequency units are also of tonpilz design, with independent drivers, independent head masses, and a common tail mass. The use of a common tail mass simplifies the design without compromising high frequency operation. The design leads to more efficient operation at both frequencies by minimizing the head mass to tail mass ratios.