One sub or two?

I just added one sub to my analog system. I can't locate it or specifically hear it. However, if I turn it off, I notice it and the missing LF. I have a fair sized room 17d x 35w w/14ftcathedral ceilings, a 8ft wall behind and another 17 x 35 kitchen/dining room on the other side. The sub is set about half way. It's a NSM 15EXP with a10in driver. Plenty of bass for me. Mated with C & C Abby's.

I just switched from one Martin Logan Abyss to a pair of Emotiva X-REF10 subs. I never really made a huge effort to dial in the Abyss; that said, I'm not done with the options for doing so on the X-REF10.

I started with a single X-REF10 to get some idea of the room modes and best guess for crossover frequency and phase settings. After that, I installed the 2nd sub. Both are symmetrically located on either side of the centerline of the front wall, maybe 1/3 the way in from each sidewall. (My room is 22' x 13' x 9', and my system is on one short wall.) The difference with 2 subs, while not huge, was definitely noticeable. HOWEVER, I use small monitors (Von Schweikert VR-1) and I have the subs crossed over at a high frequency (125 Hz). So, it's not surprising I can tell the difference between a single mono sub and a pair in stereo.

As others said, depending on your mains and your crossover method, it may not make a big difference to go with a pair of subs.

I've had 2 Rel Storm III's in my system for several years now. They are paired with Audio Physic Virgo II's. I can't live without the bottem end extension and inhanced upper bass/lower mid-range that running 2 in stereo provide.I run the Rel's (high level) directly off my Virgo binding posts. I plan to go with a full range speaker someday, Revel Salon or Wilson Shasha, once I have heard them in my room A/B-ed with my current system. I have tried in the past but it is hard to beat this setup.

According to Jim Smith in "Get Better Sound", stereo requires two subs for proper imaging; one sub is fine for home theater.

I owned a single REL Storm III, then added another and hooked up as true stereo. I like this setup. And I have owned several other REL subs - they are all awesome, but I definitely prefer the "ST" series over many of the newer models... I LIKE DOWNFIRE!!!