Can you show the plot? Or just provide some actual numbers at 30 or 40 Hz, for example
Sure. Please take with a grain of salt, others may chime in with valid feedback on why my measurements are faulty or misleading. I'm learning as I go via searching online...and all my measurements have some kind of room correction applied which may invalidate the whole thing.
Going from highest to lowest. Teal is the two SVS 3000 micro (called SVS from here on out) calibrated with Dirac Live Bass Control. No manual delay set by me. Just got DLBC a few days ago as a beta test.
Blue is two SVS with a miniDSP SHD and Dirac. I set the delay here at 8ms. My reasoning was 6ms for the DSP in the SVS (or so I had read) plus 2ms for distance. I tested all around 8ms and this gave me good frequency response at the crossover. Had no idea what group delay was at this point, it was one of my earlier measurements.
Purple is two SVS with a miniDSP SHD and Dirac. I set the delay here at 18ms. I read a guide here on ASR about subwoofer alignment by comparing step responses, using the REW alignment tool, and other things I had never heard of. Gave it a try, saw 18ms delay and thought no way, that's too long, makes no sense. The FR was great and the drop in group delay was noticeable. It's at this point I'm looking up what group delay is.
Orange is two REL T5X. Running Dirac via PC with no delay. Very early measurements, the REL had other issues and I had no idea what group delay was at this point.
And for fun, black is two SVS and Audiolense. Since I got the multichannel interface to test DLBC, and I had heard of Audiolense and Accourate for a while, thought I'd give one of them a try. It certainly made a difference in group delay, and it is certainly noticeable with the standard caveats of not blind, subjective, etc. These are linear phase filters if I am remembering right, aiming for time domain correction. And the latency with how I have things running is pretty high.