Many subs are poor in making strong vibrational effect. Also, to get the most vibration from them, you need to move a lot of air - so the enclosure must be semi-airtight.. and the voume level must be sick loud. Even with all that.. you still will not feel as much vibration as with a bass shaker.
Bass Shakers work on the concept that low bass is mostly felt and not heard. Its basically a sub without the air movment. Instead, it moves a weight inside it, and the vibrations are transfered right into the thing you mount it too. Even at very low volume, you will feel everything.
There are 2 versions available still from parts express. I have the low power versions, and when i mounted 2 under my pc chair - at maximum power, i could barely see my monitor cause the vibrations were screwing with my eyes! (pictures was all over the place) However, a thicker wood may need the more powerfull Pro version. Pro specs:
Specifications: *Power handling: 50 watts RMS/75 watts max. *Impedance: 4 ohms *Usable Frequency Response: 20 to 100 Hz *Fs: 40 Hz *Force Peak: 30 lbs. per ft. *Dimensions: 6" dia. x 2-1/8" H *Net weight: 4 lbs. each.
30lbs of force per foot generation is pretty damn sick!
pro:
http://www.partsexpress.com/pe/showdetl.cfm?DID=7&PartNumber=299-028regular:
http://www.partsexpress.com/pe/pshowdetl.cfm?&DID=7&Partnumber=299-027&raid=2&rak=bass%20shaker You should use a small amp to give them extra power, and a crossover to limit the high frequencies. While these can play higher frequencies, that will limit the more powerfull shake ability.
ohh, and heres a BYO transducer page I found:
http://www.sdinfo.com/volume_4_2/tactile.html Look up bass shakers, and you will find many reviews, as well as pages on people who use them in everything from Home Theater, to gaming chairs, and much more.
There are other transducers out there - but they cost a lot more too.