Anybody heard of Bass Transducers?

Looking into my Car Stereo Cookbook again, I came across Bass Transducers.  Anybody ever heard of these?  "Working on the principle that low bass is mostly felt and not heard, bass transducers directly vibrate the chassis of your vehicle.."  They say when working in conjunction with subs, they can give you the sensation of extremely powerful bass with zero boominess.  Has anybody heard of these before or worked with them?  Are they any good?  Examples are Aura Bass Shakers and Alpine Bass Engines.

muppetmaste, i have seen and tested a few of these devises. The principle is sound but has a few limitations. Rumblers couple low frequcy vibration to the interior of the vehicle.very similar to to the effect of a normal subwoofer when it causes the vehicle to start to resonate and cause extra  output at that resonance. P.G used to make a cool device called a cyclone. that did a great job of producing real low bass by moving air with a spindle in a tube similar to a washing machine type set up . the long and the short of it is These devices do not replace a subs unless your front end is going real low and or you got some real good mid base.Steve@A.E.S

how about in conjunction with a sub in a small space?

sq