Abstract: An underwater sound generator composed of a ferrofluid contained within a toroidal container which has a rigid bottom and top and elastic cylindrical side walls. A coil of wire links the toroidal container and is adapted to be connected to a dc bias source to produce a biasing magnetic field, H.sub.BIAS, which drives the magnetization of the ferrofluid well into saturation. Two oppositely wound coils of wire respectively link the inner side wall and the outer side wall and are adapted to be connected in series to an ac signal source to produce a time-varying magnetic field, H.sub.AC, which modulates H.sub.BIAS. The wires are equally spaced in the volume occupied by the ferrofluid. The gradient of H.sub.AC in the radial direction provides the time-varying force on the ferrofluid. The resulting ferrofluid motion in the radial direction is transmitted through the outer elastic side wall to supply acoustic motion to the surrounding water.