Any good, highly damped sub that's been digitally corrected. Compensating for the room's destructive effects down below 100hz or so is a game changer - IMHO. I use a Velodyne SMS-1 DRC unit with a pair of Rythmik 12" subs. The Rythmiks are a very fine design, but real world priced with no pretense to SOTA status. Still, they beat the hell out of any of the non DRC units that I've heard.
Again, just my own HO.
Marty
Again, just my own HO.
Marty