This is where the tale gets even better.

With the multiple subs etc, the bass response is incredibly smooth throughout the whole room. In effect everywhere except right at one of the subs. I can tell just by walking around and listening / feeling.

I did do my calibrations at the sweet spot BUT I actually placed the mic in several other positions around the room (on other chairs, on the floor in a couple of places, on a rack of DVDs, etc.) and the response in each case was incredibly flat. Most of the time there was just a change in the upper frequencies and a little bit elsewhere. So much so that a few times I had to "talk into the mic in a Lou Rawls sorta way" to see an honest-to-goodness bumpy trace. This was all with three subs running.

Given my experience with just one sub running, measured at the sweet spot, I would guess that the room response would be quite "lumpy" throughout with just the one sub running. When I run just one sub and walk around, I can really notice the peaks and dips.

I suspect that the greatest reason(s) for this extremely flat response are:

1. The use of three subs
2. The fact that they are not all identical types. In my case the Velos seem to provide the lowest end while the B&W handles the upper end - at least from what I saw when I did them one at a time
3. The placement of the subs.

As far as acoustic treatments go, I've actually not added anything specifically targetting the bass region - like bass traps. I have treated about 50% of the wall and ceiling surfaces with acoustic panels - but they really target the mids and highs. The bass taming is really done through layout and the fact that the entire rear "wall" is in fact my equipment rack / heavy curtain - which then opens up to the rest of the basement. The floor has a nice area rug - on concrete. The furniture consists of three minimal leather / wood chairs and ottomans (IKEA Poang) - so there's no huge bass absorbing sofa.

It's probably as much good luck as good planning - but without the planning it never would have been.

ps. I actually run four subs. The fourth being a homebuilt (using Polk drivers / passive radiator) with an external NAD power amp. It's fed the output from a dbx100 ("subharmonic synthesizer") which I use "to taste" (and in moderation) depending on the source material. It's basically reproducing artificial bass in the 27.5 - 55 Hz range. It's particularly usefull with recordings that are bass-shy to begin with. Since it is used in addition to the other three subs, the SMS-1 calibration was done with it turned off. Come to think of it, when it is off it might even act as a bit of a bass trap - with its 15 inches of driver surface area being vibrated by the surrounding air pressure. But that's just a guess on my part.

Jeff Mackwood