One sub or two?

Two subs provide a lot more flexibility. It may be easier to place two small subs (two 9" cubes in my 2-channel system) than one larger one. Two can help break up room nodes that cause standing waves. Improperly done two subs could be out of phase and cancel out the lowest notes, but properly done they will reinforce each other. For a good, coherent stereo image, the sub(s) should be in a consistent geometrical relationship with the listener and the main speakers. With a single sub you are often limited to a narrow range of ideal listening positions. Two subs make it easier to maintain a consistent geometry throughout the room.

A second sub also adds at least another 3 dB dynamic range.

I have two subs in both my 2-channel analog living room system and the 7.2 channel HT rig down in the family room. In each case there was a noticeable improvement in the clarity, imaging, and dynamic range when I added the second sub.

Two subs are better. No question about it. I've tried it both ways.

Just bought 2 M&K 150 watt 8'' subs. 2 will spread throught the room better. And, at 190.00 each, the deal was good. Sometimes I use just 1 for AB comparison, but I'm glad I got 2 small subs instead of 1 big sub, at lease for 2 channel.

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.