Avnx,
the 92 uses an active vibration system where a computer controls a set of elecric motors with excentric weights that spin as commanded to create counter-vibrations. Works very well, we have 3 of them around the aircraft, and sensors on the cabin and cockpit floor. the computer sorts out what is needed to keep things smooth. We also have a bifilar on the rotor head. the system tunes to any rotor rpm, so it does not go off tune in autorotations or approaches.
see
http://www.s-92heliport.com for some data in the presentations that you can download.