When I first installed my 4 SubMersives, I used Gain Matching (see description by CraigJohn in the SubMersive thread) and never paid much attention to what might happen if I level matched. When I built my new theater, I also set up the subs with gain matching.
A few weeks ago, I decided to try level matching and see what happened. This was prompted by reading about a few different multi-sub set up procedures and my own curiosity. The audible results were significantly different (can't tell you why since the FR looked virtually identical after Audyssey did it's thing). And for a while, I REALLY liked it for moves but not as much for music. The bass in movies was just stupid (good?). Over time, I began to hear things in some parts of the bass spectrum (in movies and music) that did not sound correct and the bass in music sounded "thick" in some instances.
So I decided to compare the uncorrected FR of the two methods. Since my front subs and rear subs are different distances from the MLP, I grouped them that way and assigned
the fronts to Sub Out 1 and the rears to Sub Out2. Of course Audyssey set up different distances (and trims) for each group of subs. The actual level of the gain matching FR was a bit lower than the level matching, I adjusted them to be the same when I plotted and compared them. Here is the plot:
As you can see, Gain matched provided better uncorrected results.
The next plot is after setting the sub distances the same and comparing that to the Audyssey assigned distance for each sub group. You can see the huge dip near 100hz.
Finally, I started physically moving the rear subs, used gain matching and ran all four subs from Sub Out 1. What I ended up with is FR almost as good from 20hx up (the dip around 100 means nothing since (1) Audyssey fixes it and (2) I crossover below it. What I gained is very nice relative increase in output below 20hz.
FR after Audyssey does its magic (no smoothing - true for all plots):
As Craig noted in a previous post, if you use both sub outs, Audyssey uses level matching so you would need to split the differences in the two trim levels that Audyssey selects. I don't have that issue in this approach.
Sonically, I love how it sounds for movies and have not listened to music but will do so later today. It sounds better from an accuracy perspective than any time I have owned them but not as much fun as when I had level matched them - but I have yet to hear the thickness I heard when they were set up that way.