This is like a gimmick used in home theaters. A good friend who is quite a bit into HT has additional subs called the "butt-kicker" (IIRC). They are simply a vibratory module that is mounted to the underside of the platform on which the theater seats are bolted on (fake platform).
Guessing the real LF signals not heard by the human ear are translated into mechanical energy. Great for earthquakes, thunder and lightning.
