Is it better to have two matched subs or one

In general, the in-room bass smoothness improves as the number of intelligently-distributed bass sources increases.  So yes, two subs should be a worthwhile improvement over one, assuming you place them fairly far apart and at different distances from nearby room boundaries.  

Duke

Duke is certainly more qualified than I, but let me add that unlike the dedicated sub channel in home theatre sound, summing stereo bass into one channel can actually subtract some bass signals.

More is better unless you can't afford them or don't have room for them.

2 is better than one, especially if you can locate each in the optimal locations, which is usually not symmetrical.

unsound/duke, how does it subtract some bass signals?

I use single-end stereo out from an Ayre preamp to a Velodyne SMS-1 bass manager that presumably sums the channels into one balanced channel that I split between two HGS-15s subs.

There are at least two alternatives:

• The SMS-1 has three single-ended outputs. I could take two of those to the subs. Not sure if they are summed outputs.
  
• I have a spare SMS-1. I could take balanced LR from the preamp to each SMS-1 then balanced out to each sub. Set up is more complicated.

With the current setup, I’m unaware of the subs unless a pipe organ pedal note is invoked, but they do seem to make the setup sound a bit larger with large orchestrations.

Any advice-- and from you too erik -- would be appreciated.

db