I run three SVS sealed subs, two SB-2000s set at 60Hz and 50Hz, and one SB-3000 set at 40Hz in a modified DBA/swarm set up in a 17 x 21 x 10 foot sized room. Volumes are set low as mains run full-range currently. It blends in well and cements the real bottom end nice and tightly. They replaced a great REL Britannia B1 sub.
Lots of good sub mfrs these days besides SVS, but I remain very satisfied.