Originally Posted by AustinJerry
To be honest, when I have moved subs around looking for the best position, I have never adjusted the distances in the AVR during the process. I am not sure it is that important. If you are obsessing about sub distances and changing them every time you move a sub, you may be doing more harm than good.
I repeat, I have never gone to this trouble when moving my subs around. Perhaps someone else can share an opinion as to whether they think this is necessary or not.
Yes, it makes a difference.
It has to do with phase cancellation. When the subs are not equidistant to the MLP (especially if the difference is significant), changing the individual delays so the direct wave arrives at the MLP simultaneously ensures that it is in phase. If you don't change the distances and have one sub closer than the other (or move one sub more than the other after running a brief calibration for Audyssey to set the distances), the direct wave could be out of phase, producing what looks like a null due to the cancellation.
If you move the subs around looking for the best positions in the room but don't change the distances/delays, you could end up ruling out, and missing out on placement positions that could produce great results, because not changing the distances produced this phase cancellation. I saw this when I was trying to find the best placements for dual subs. It occurred to me due to the distance tweak, i.e. if inaccurate delay settings for the subs could produce a dip in the bass region that could be fixed post-calibration simply by altering the delays, this must hold true for the unEQ'd response as well and measurements confirmed it.
That's why my recommendation was to measure the inherent delay in the subs by comparing the measured physical distance vs the Audyssey detected sub distance while measuring each sub separately. Then, when moving the subs, you simply adjust the distance settings + electronic delay in the avr after each move, and see which placements result in the best pre-EQ results. run the calibration in that position, then if necessary, adjust the avr distance settings to the measured distance + electronic delay already determined, to see if that removes any dips.