It's interesting that the top-of-the-line Bryston subs are using 8" drivers.

http://www.bryston.com/products/speakers/Model_T_Subwoofer.html


M60ti, VP180, QS8, M2ti, EP500, PC-Plus 20-39
M5HP, M40ti, Sierra-1
LFR1100 active, ADA1500-4 and -8