A hydroacoustic transducer for generating and applying acoustic energy to a load coupling structure has a hydroacoustic amplifier with a driver stage and a power stage. The power stage includes a valve, which obtains high power conversion efficiency by operating to switch the flow of pressurized hydraulic liquid on and off thereby providing a switching amplifier which presents a pressure source of acoustic energy. This source is connected to a load coupling structure by way of an acoustic transformer and an inertive element in series with the source. The inertive element is provided by a liquid-filled bore and is terminated at its input end by the larger area of a stepped piston which provides the acoustic transformer. The smaller area of the stepped piston is in hydraulic communication with the power stage of the hydroacoustic amplifier. The series combination of the transformer and the inertive element resonates with the load coupling structure and provides a band pass frequency response characteristic with the load coupling structure. The hydraulic transformer reduces the input acoustic pressure levels from the amplifier, which are then raised again by the inertive element in the series tuned circuit including the inertive element and the load coupling structure, thereby allowing operation at pressure levels which avoid cavitation in the liquid filled elements of the apparatus as well as providing impedance matching between the hydroacoustic amplifier source and the load. The inertance of the inertive element may be varied with variation in frequency of the energy generated by the amplifier (over frequency sweeps) to maintain optimum tuning of the structure.