Abstract: In combination, a water bed frame with side boards, a water filled flotation mattress within the frame, an electromagnetic vibrating transducer unit between a side board and the mattress and operable to generate and transmit motion into the mattress and an adjustable power supply connected with a 60 Hz. domestic power service and delivering current at a fixed frequency and at sub-harmonic frequencies of said fixed frequency to the unit; said unit includes an elongate resilient armature with front and rear end mounting means and fixedly mounting the rear end portion of the armature, an electro-magnetic driver fixedly mounted in predetermined working relationship with the rear end portion of the armature and receiving power from the power supply and a tuning weight on the front end portion of the armature to increase the mass thereof and shiftable longitudinally to tune the natural frequency of the armature into synchronism with the frequency of the power delivered to the driver.