A speaker including a supporting structure, a diffusion membrane that is movable relative to the supporting structure, a motor for actuating the diffusion membrane, including a movable unit relative to the supporting structure, the movable unit being mechanically connected to the diffusion membrane for synchronized movement thereof, and a hydraulic circuit interposed between the movable unit and the diffusion membrane, the diffusion membrane and the movable unit each including a movable piston surface, interacting with a fluid of the hydraulic circuit.