Garebear,
All subs require knowledgeable setup...generally done via a combination of 2 ways: physical placement and the crossover, phase, volume, etc of your subs controls.
Physical placement.
- you'll have to experiment...corners can emphasize bass which can be good or bad.
- Auralex subwoofer platform. stunningly good and relatively inexpensive...60 bucks. Cleans up bass from vibrating thru floorboards...you end up turning the bass louder, but at least its signal from cone...vs vibration thru your floorboards and furniture
Crossover, phase, etc.
- Not everyone cuts off their main speakers. With Cremona Ms...experiment both ways. I ran my Guarneris full range rather than cut off and ended up preferring it this way...mainly due to quality of crossover in my Velodyne
- Phase: They should be in phase (not out of phase). To tell, reverse the leads going into your sub (or your speakers)...keep playing around with the phase knob on sub til bass seems to be at its LEAST...so sub and speakers are OUT of phase with each other. Then reverse the speaker leads back...now you're IN phase.
- CDs: Amos Lee (close-miked guitar...great to seeing if your sub is 'bleeding' too high up into the upper bass/lower mids. Nirvana Unplugged...great for kick drum speed, naturalness. Ame: anything by these guys for deep, propulsive electronic house/deep bass
In addition to the above, Velodyne allows you 8 different bass frequencies and an equalizer to further tailor for 'nodes' in your room which accentuate or cancel out various frequencies...quite typical in rooms.
Not affiliated with Velodyne in anyway...just satisfied with them. Heard JLs superior by far, but the variability of the Velodyne hookup is helpful to someone like me who isnt an expert or techie.
Finally, as to 2 subs or one...the main reason is that having 2 sources of bass should allow you much better ability to smooth out bass response across the room. It is not about bass power per se, though that too can be improved. Its mainly frequency response smoothing throughout the room.
When you've got a room where you end up placing the sub very close to one seating area...then [sometimes] sitting elsewhere means you get very different bass response. Having 2 (ideally 4!) can help smooth this out. But not all of us have the room, funds...or the time to mess around with ideally setting up 2 subs. one can be tough enough.
hope that helps...good luck.