Human hearing is designed to gather far more information from the environment than we are at present able to measure. It is no problem at all to know whether you are in a closet, car, living room or concert hall even with your eyes closed by hearing alone.
Consequently, the more closely we recreate the sonic signature of the recording venue the more realistically it feels like we are there.
This is the first thing that hits you with a DBA. I mean, unless you crank it up to where you notice the extra bass. That is too much. With levels properly set you will never know there are any subs at all. People have to be reminded about mine even though they are all around the room obvious as hell. They just don't seem to be doing anything.
But the effect is noticed even on recordings that seem to have no low bass. The speakers and room disappears, the sound stage expands, and there is a sense of envelopment.
I went through this first when adding multiple subs. Then again to a lesser extent when putting the subs on springs. Then again to a much greater extent when putting the subs on Pods. Each time the bass did improve a bit but this was only noticeable with music with obvious bass. The improvement however goes far beyond this, extending well up into the midrange and also with the really wonderful feeling of envelopment, of being in the sound stage instead of merely looking at it.