One sub or two?

If you cross over to the subs very high (>100hz to 150hz), there are 3 very clear POTENTIAL benefits to a pair of subs vs. a single sub. However, the key word is "potential" and the ability to realize that potential will depend upon - among a few other things - what device you use to effect the crossover.

1) At a sufficiently high x-over points (per above) you can maintain stereo integrity.

However...

At some point - people seem to debate exactly what point - the crossover frequency is low enough that bass becomes monophonic and this benefit does not persist, per Phasecorrect.

2) Careful placement of a pair of subs will provide MUCH!!!! smoother FR in most rooms. Not even close. This is IMHO the biggest benefit of a pair of subs BY FAR. IME, a subwoofer almost always interacts with the room to create peaks and dips that will exceed +/- 10db at the listening position. A pair of carefully placed subs can reduce that to +/- 3 or 4 db. This is an immediately audible difference.

However....

If your x-over is effected with a PrePro that has Audyssey, ARC or similar digital room correction ("DRC"), or stand-alone correction/x-over like the Velodyne SMS-1, you can get to the same place by EQing a single sub.

3) You will always get more clean output potential from a pair of subs than from a single sub (assuming that the subs in question are the same model).

However...

A single high output sub may cost less than a pair of lower output subs.

Bottom line:

#2 is the key. If you are using DRC, a second subwoofer is a nice luxury. If you are not, a second subwoofer will almost always provide VASTLY smoother bass response.

All IME. However, ME is now up to 5 years of continuously tweaking subs in my system, so I feel pretty good about this advice. I really doubt that YMMV.

Marty

I went from dual NHT subs with an NHT X2 sub crossover to a single REL Storm III using speaker level connections. In my room, the Storm III was a nice improvement. But it must be said that I am lucky enough to not have any nasty room modes and I am crossing over quite low at 40Hz. And damn do the REL subs integrate well with speakers.

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.