Graviman,
The vibe system on the S-92 (and the EC225) Use "force generators" which are solid state electric motors with extreme precision rpm control. They also have a built in counter weight system that can be driven off center so they can change the force the put out. They can also change the phase of the spinning so that they can determine the direction that the force is exerted. Thus, they control the frequecny, amplitude and phase of the vibratory force. A set of vibration pickups in the cabin floor read what each seat is experiencing, and send their readings to a computer that then compares the readings, remembers the best way to juggle the forces, and then adjusts the several force generators to get the best ride for all.