Subwoofers.... one 10" or two 8"?

With all due respect to gdhal, I went with a pair of SVS SB1000 to fill out the bottom end from some Silverline Prelude Pluses.  The Pluses have surprisingly good bass for the size of their drivers.  If all I listened to were, say, acoustic jazz they would be completely adequate.  BUT things being what they are, I wanted a little more so ordered the SB1000s.  The Silverlines run full range and the subs are connected via speaker level input from amps.  The subs are positioned next to the floor standers and crossed over at around 100 Hz.   I listen about 8-10' from speakers that are 2-3' out from front wall in a ~19'x21'room with an open back wall (i.e., wall behind the listening position).  Subs disappear but give Tony Levin's bass a nice growl and make Bela Fleck's Cosmic Hippo sound amazing.  The system is posted if you want to take a look.  Good luck in your decision.

lars- 
Try both ways of hooking up your sub(s) and hear which sounds best to you.  I can run the SVSs with either high level or line level inputs.  I had thought line level was the better way to go (running floor standers full range and using a 2nd set of preamp out connections to the subs) but found a speaker level connection sounded better to me...thought things sounded "fuller".

@leotis 
Your 8/13 2:27AM post seems very helpful.  THANK YOU.

I'm planning to try it integrating SVS SB1000s with Silverline Prelude Pluses that claim a lower end of mid 30s Hz.  

For anyone interested, an on-line tone generator is available at the link below.

http://www.szynalski.com/tone-generator/

oleschool -
Reasons for going with the SVS SB1000s are:
1) sealed design
2) 12 inch driver
3) rated into mid 20 Hz
4) small size
5) weight - I can move them around without needing a chiropractor
6) continuously adjustable gain & cross over as well as phase
7) line level and speaker level inputs
8) 45 day money back in home trial (free return shipping during that time)
9) 1 year money back on trade up
10) 5 year warranty
11) generally favorable reviews...both consumer and professional
12) great price (got a pair of SB1000s for <$1000 with free shipping)

Still messing around with settings but they look like keepers. Only thing I’m not crazy about is the black ash finish. Wish they offered a mahogany or cherry...even if it were veneer.

leotis - YES, RH of TAS. I might have muddled things together having read a couple of pieces about that  method including the one at the TAS link you provided.  I think RH contributed as well to the Sound + Vision article I read.  Did see his name...maybe in the comments section.  

The subs are located right next to the main speakers so that’s not a complicating factor. Some say not to go this way, others recommend it. The folks at SVS were okay with it as they say their subs do not have to be "boundary loaded".  They appear to be giving acceptable performance in this position and just need a bit of tweaking. I’m inclined to repeat the out of phase/phase setting experiment though as I mentioned results after the first attempt were not "ideal" in terms of overall impact on the music.

@leotis -
I found that same procedure you recommend (setting sub's phase based on minimizing bass output at the crossover frequency while while main speakers are in reverse phase to sub).  It was actually in Sound & Vision and submitted by Robert Harley as I recall.  I didn't do the out-of-phase-on-the-mains part but did try maximizing dbs at the crossover frequency using a tone generator.  I will repeat the procedure to confirm but it seemed like a large change to my almost 0 degree initial phase setting was needed....going to 140 degrees! Both channels ended up at the same phase value and I was not trying to read the actual setting at that point...just going by ear with what gave the loudest sound.  Anyway, afterwards,  I was not very satisfied with overall impact on music.  It seemed like soundstage had collapsed and (lower midrange?) was weakened.  At this point, I'm inclined to agree with Erik that this method may have unintended consequences.  Based on what else I'd read about phase differing across a range of frequencies this is, perhaps, not surprising.  I'll probably repeat the experiment BUT I suspect setting phase is going to be trial and error based on the overall effect on the music and not just max db at the crossover frequency.

To anyone interested, I repeated the out of phase/phase setting experiment using the on-line tone generator posted above and a Radio Shack SPL meter positioned approx. ear level at the listening position.
I ran measurements from 200 to 10 HZ for the Silverlines alone with volume at 200 Hz set to 80db. Observed values generally less than 70db for 50 Hz and lower (a slight bump to 70 & 74 db for 40 & 35 Hz, respectively). Decibel levels at 80 Hz were virtually identical (i.e., 82/83 db) for 0, 20, 80, 100, 120 & 140 Hz. At 160 degrees, a slight reduction to 80 db was observed. A value of 77 db was measured at 180 degrees. I did not find a huge null created by running the subs out of phase to the main speakers. I wonder if this has to do with the great disparity in speaker sizes (one 12" SB1000 driver vs four 3.5" mid/woofer drivers in the Preludes) or if it is due to "reinforcing" room effects. I did listen to quite a bit of music afterwards with connections properly matched between subs and mains and with the phase now at 180 degrees. Did not notice any of the negative effects previously reported with phase at 140 degrees. Possibly the ("sub") bass was a little better at 180 than at 0 degrees but it was very subtle if not a placebo effect.