Big difference between the beasliest subwoofer and the beasliest subwoofer DRIVER. Beastliest subwoofer has to be a tie...two subs, both built by Tom Danley with Danley Sound Labs (my home theater is all Danley), both for the military...
Sonic Boom Cannon...135 db at 10 meters away. Not impressed?...forgot to mention...that was at TWO HZ!
Matterhorn Subwoofer...again, military build, but they will sell you one in case you have a stadium you want to put an LFE system into. 125 db at 20 hz. Again...not impressed? Wait for it...at SEVEN HUNDRED AND FIFTY FEET AWAY!?! Okay...yes, it is built inside a shipping container, making it somewhat inconvenient for a daily driver... and yes, it would require a huge generator to run its 40 kilowatts of 120 volt power. So, you will meed a big rig for it to work(beastly, sub...beastly vehicle). Vent it into a car/truck cabin and it would probably shred the cabin...which would be amusing as heck to watch. But it is currently the ultimate in beastly. Turn it on in a neighborhood and you can probably break windows and maybe do some structural damage...which would likely annoy the powers that be. Tom sats he can scale it as large as you want...matbe one of those 40ft shipping containers?
As for a driver? Easy...Eminent Technology Trw-17. It isnt a woofer...it is a fan which frequency modulates the air directly. One of the most frightening drivers to watch in action...want to talk beastly...that thing could hurt you. Low frequency cut off for those who want really low extension? 1 hz. Make friends with your glass repair man. Infinite baffle install. So you would need to leave the trunk open when playing, but beastly means no compromises. Runs about $25,000 installed. Moslly used in big home theater installs where extension is king and we dont have cabin gain.