My main systems have a crap-load of 8" woofers.
Main 2-channel system speakers are 8" Tannoy dual-concentrics,
HT left, center and right speakers are EPI 150s.
I also have a total of three subwoofers- one in front, with a Dayton Designer Series 8" DVC driver, and two, behind the couch, with EPI 8" woofers. All three subs do also have 15" passive radiators. And play to BELOW 20Hz flat, in-room.
The only active woofers in that room, that aren't 8", are the 6.5" woofers in my HT rear speakers- EPI 50s....
Funny enough- the audio system in my Mazda Protege, ALSO has four 8" woofers. An EPI 8" in each front door (playing from the lowest bass, up to 400Hz or so, active crossover), and two more EPI 8" in the rear deck (crossed over to where they only play between about 20-40Hz), all in effectively infinite- baffle. That system is also flat to very close to 20Hz, and will make the air literally palpably shake, in the car, on pipe organs...
The speakers in our upstairs system (living room) have 6.5" woofers- but in pretty large cabinets. Vifa C17WG69, in 2 cubic feet enclosures, tuned to about 28Hz. Plays flat to below 30Hz. Enough to not need a sub, with TV/movies. We don't play it that loud, and under these conditions, it's plenty. The crazy thing, is that it will play LOUDER at 30Hz, than at 60Hz, before it bottoms out- the port is SO effective at reducing cone motion at port resonance, that the cone moves LESS at 30Hz, than at 60Hz, at the same SPL level...
Regards,
Gordon.