Clean bass needs a Q of 0.7 or less and two 15 inch woofers in most domestic settings. (4 x 12" woofers will be equivalently capable.) I rarely see this kind of setup on Audiogon so I don’t think many people are even aware of the issues raised by Erik.The Classic Audio Loudspeakers that I have (model T-3.3) use dual 15" drivers, one forward firing and one down firing. The model T-1 employs a 15" forward firing and an 18" down firing. Both cut off at about 20Hz and are 98db 1 watt/1 meter. I regard the bass as very musical- its is very nuanced and has plenty of wallop.
A subwoofer system that solves many bass/room issues is the Swarm by Audiokinesis. It employs mulitple small subs and so effectively reduces room nodes, standing waves and the like.