Each of a pair of electrically conductive spiral coils is ensconced in a disk-shaped matrix. The two coil-ensconced matrices are joined face-to-face so as to sandwich between them a thin, non-magnetic elastic layer. An electronic device is connected so that each coil and a corresponding capacitor form an LC circuit. Electrification of the two LC circuits results in the departing and returning, in oscillatory fashion, of the two coil-ensconced matrices. This resonant behavior is both electromagnetic and mechanical in nature. The intermittent electromagnetic repelling is related to the LC circuitry and the oppositely polar electrifications of the respective coils. The springy mechanical activity is based on a spring-mass model and involves the elasticity of the intermediate material and the entrainment of ambient fluid. The dual oscillatory modes are merged at the same frequency through tuning of either/both oscillatory mode(s). In many applications, an inventive acoustic projector produces pressure waves underwater.