Method, source and seismic vibro-acoustic source element (10) configured to generate acoustic waves under water. The seismic vibro-acoustic source element includes an enclosure (20)having first (22) and second (24) openings; first and second pistons (30, 32) configured to close the first and second openings; an actuator system (40) provided inside the enclosure and configured to actuate the first and second pistons to generate a wave having first frequency; and a pressure mechanism (70) attached to the enclosure and configured to control a pressure of a fluid inside the enclosure such that a pressure of the fluid is substantially equal to an ambient pressure of the enclosure.
