A portable low frequency underwater acoustic projector having two circular diaphragms separated by a spacer ring with a pair of coils and oscillating masses being located in pipes connected to central opening in two diaphragms, the coils driving these masses in opposite directions. Central openings in each diaphragm have an associated pipe extending outward from the interior of the projector, the pipe having closed outer ends. The interior of the projector being gas filled to provide pressure compensation.