Getting there: From the test CD link in the link:
All modern, powered, sealed subs have a phenomena called group delay so to best integrate sub(s) you must fix that timing issue so the sub lines up in time with the mains at the crossover point. Since you cannot remove this inherent delay in the sub you must add this delay to all the top channels. You do this by manually setting the speaker distance settings in the setup menu. I suggest setting all the distance settings THE SAME and to a LOW number (for example 7 feet; then add 12 feet to the SUB distance only (so the sub distance now = 19 feet). Now you have added the correct amount of delay to the REST of the system (the L C R Ls Rs) so you can then properly FINE TUNE the sub's phase with the mains by adjusting the phase knob and polarity switch on the sub. Therefore you have added just a bit more delay to the tops to give you a space for a fine-tuning adjustment on the sub to sharpen the focus. This will give you the best possible impulse response through the entire system; the imaging and focus should then should be uncanny, and the bass focused and as tight as possible. If this is done correctly, even if the subs are behind you, you will NOT localize them; it will seem as if the bass is playing from the front of the room, where it belongs, and this is true even if the crossover frequency is as high as 120 Hz.
I think I get it, what I don't get is that author went through a very detailed, yet simple, scientific based manner to explain the problem but then offered what I think might be a sort of layman or feedback-less manner to solving the problem. Why would 12 feet be the magic number? Wouldn't different subwoofer driver mechanics or enclosure types (sealed, ported or something even more rare like I have an infinite baffle) introduce a variance in electro-mechanical delay in the output chain?
If I remember correctly (I'm not a home), my FL distance was 10 feet, my FR distance was 10 feet and my center was 9 feet. If I add 12 feet to these distances I'm at 21 to 22 feet. As I noted in a previous post it seems that as I drifted away from 1ft the SPL @ X-over was reduced but started coming back as I got into the upper low to mid twenties. Unfortunately I did not take any measurements at 20, 21 or 22 feet. I believe the closest measurement other than 25 feet was 18 feet. and 18 feet did not look good. 25 feet looked better.
Would it be your recomendation at this point to start with a sub distance of 12 feet greater than my mains and then tweak a few feet from there according to my REW measurements?
Also, why would I set all of my "other" speakers to the same distance setting? Luckily my front soundstage is very close in distance (within 1 foot tolerance) but when it comes to the surrounds, particularly my back surrounds a larger disparity occurs.
Is it just me or do most threads here focus on frequency response only and not these timing issues?