Is it better to have two matched subs or one

Contrary to popular belief bass can be stereo. If the bass driver from one channel is moving in the opposite direction of the other channel, when summed they can cancel out the signal between them.

@dbphd asked: "unsound/duke, how does [summing stereo bass] subtract some bass signals?"

In theory to the extent that the left and right channel bass signals are out of phase with one another, the resulting net electrical signal would be less than 100% summation. And in theory if the left and right channel bass signals are 180 degrees out-of-phase with one another, their electrical sum would be complete cancellation.

In practice, I don’t think this is a significant issue. I’ve run multiple subs in stereo and in summed mono and in dual mono and have yet to notice a difference which could be attributed to some bass signals being subtracted.

It is my understanding that true stereo south of 80 Hz or so is rare at best. 

Real (or synthetic) stereo bass can offer an enhanced sense of immersion in the acoustic space of the recording. 

Duke

Duke,

" Real (or synthetic) stereo bass can offer an enhanced sense of immersion in the acoustic space of the recording." That has been my experience and why I believe most systems benefit from using subwoofers. 

@salevick - How big is your listening room? 
Is it a dedicated room or shared living room, etc.? 
Do you have a budget in mind?

Hello salevick! For classical music, one is fine. For more ooomph in pipe organ music, percussion, etc. two is obviously better. The big reason for one per channel is home theater use. Crashes, alien approaches, creatures in the bushes sneaking up on you are better since a creature menacing from the left side should not have heavy footsteps thudding from the center of the room. Many TV documentaries and nature programs (BBC stuff in particular, PBS series also) have marvelous multi-channel soundtracks. I have five systems in the home and I have 9 subwoofers. Keep Smiling!