Originally Posted by beanbag
I have one sub which I tried in all kinds of locations along the front wall (i.e. behind the speakers) but no matter what I would always get nasty nulls. I then moved it to a location much closer to me (nearfield) and those nulls are now gone, except for one at 26Hz. I used REW and miniDSP's built in delay to try to get the best integration with my speakers.
My understanding, phase, distance and delay are one in the same, the amount of time it takes for differing sources of co-produced sound to reach your ears.
My question is if I try to get dual subs to make the freq response smoother, do I need to have an independent volume and delay control for this sub? Most likely this second sub won't be equidistant to me.
With REW and a miniDSP, it reads like you've done the best you can and as you suggest, the next step is a second subwoofer. Even with two subs, the way subwoofer produced sound waves interact, there's a symbiotic relationship; when one peak or dip is removed, another peak or dip is created or enhanced. Very frustrating.
With two subs, on opposite walls, one nearfield and one on the screen wall, with REW and your miniDSP, you'll have much better results and you'll be quite pleased with the sound quality improvement.
What subwoofer do you currently have? What are you looking to as a second subwoofer? If you haven't already considered this point, allow me to encourage and use this as an excuse to upgrade to a subwoofer two or three steps above what you already have. If you're able, sell the old one and buy twp matching subwoofers. It's just a suggestions so please don't take offense to the above suggestion.
Our solution to this most vexing of problems was a new receiver with XT32/SubEQ HT with two upgraded subwoofers, positioned as described. We don't have a perfect graph, small dip about 52Hz but it's only a few dB more than the rest of the graph which is +/-3dB. And even with Dynamic EQ engaged, I find need to run the subs +10dB hot during movies to compensate for the volume being down, -17.5dB MVC. The point, even with two subs, XT32 and judicious use of REW for final tuning, I find need to go off the farm to get sound that meets our needs.
I left your last alone as Bill is infinitely more qualified to respond to your last question. Hope the above helps with your questions and concerns.