Four 4" VC's, 19KW RMS power handling, 21" diameter, and you get a free t-shirt when you buy it (for real!).

See

http://quadrasub.netfirms.com/qs21.htm

Pretty interesting. Saw it about a half year ago actually and just stumbled across it again today, unfortunately T/S specs arn't up but they were half year ago (think they updated woofer to a better one, so T/S specs prob changed - looks different from before).

Great for anyone that can carry a 130 pound woofer from the mailman to its sub box!