Folks,

I've used multiple subs for years - not for "stereo" reasons but rather because I've found it much easier to balance the sound (bass) throughout the listening area when using more than one sub.

In my main theatre's current set-up I've recently gone to using three subs (Velodyne Servo 1200, B&W ASW1000, and a passive home-built from my engineering design days that uses extra-high density particle board, four 6 1/2" Polk drivers, and a 12" Polk passive radiator) in what is a relatively small room. It's producing the best (admitedly a subjective term) sound that my set-up has ever produced. On top of that my mains are large towers with a tested -3db point of 27Hz - so they're not lacking much in the way of "musical" bass either.

On the subject of stereo subs, I'm sure that some people can, or at least think they can, hear a difference. In my case, using only two subs, located close to their respective left and right front speakers, I hear no difference at all - and neither do a number of fellow listeners who have done some "blind" listening tests with me. I currently use an ICBM-1 which, as you know, has a switch that allows mono or stereo sub operation, so I can switch between the two modes instantaneously. Nobody hears a difference. Nobody can tell which is mono or which is stereo. Even though I'm using two different subs, and even though there is no way that I would ever be able to match the subs up exactly in terms of output level (I use a Radio Shack analogue level meter), cross-over point (I rely on the indicated settings which are probably off by at least 10-20%), or low frequency extension (since the Velodyne goes much lower that the B&W). So despite even these differences, there is no detectable difference - at least not to my ears. I can only imagine that identical subs, set up identically, would yield even less of a difference.

Just my opinion / observation. Not that I am doubting anyone who does notice a difference. That's the beauty of this obsession (er hobby) called home stereo / theatre.

Jeff