[tomlinmgt]

The (single driver) Cain and Cain Abbys I have been using for many years are a bit bass shy, so I have subs behind and to the right and left of my listening position. It creates a wonderful sound stage and I'm continually amazed by the strength of the illusion that the bass is coming from the Abbys - 12 feet in front of me - rather than from the subs behind me, I guess you'd call it an "aural" illusion.

I had the same experience in my prior listening space with the subs on the rear 16' wall spread about 6' apart. You would never know there were subs behind the listening spot. It sounded like all bass was generated from the front of the room. So long as the crossover point is kept lower than about 80 Hz, the subs can't be localized so the bass seems to come from wherever the music is coming from. 

[tomlinmgt]

Some things to consider....

Let's say I cross my mains to my subs at 50Hz. That is a 22 foot long wavelength. So with the subs set back two feet behind the mains that is about a 16 degree phase rotation (or something like that). That was off of the top of my head.

Consider that amount of phase rotation to the delay caused by room reflections as the lower end bounces through the room a few times.

Once you get real close to being in phase, fine tuning gets really hard to distinguish or hear.

So measurements that may look a little "imperfect" (in the first few octaves) won't always translate to something that is easily heard? Or, so long as spectral balance and decay look good and it sounds good, then pack up the tools and move on?

[Danny Richie]

So measurements that may look a little "imperfect" (in the first few octaves) won't always translate to something that is easily heard? Or, so long as spectral balance and decay look good and it sounds good, then pack up the tools and move on?

I am just saying that at those long wavelengths, and with the typical room reflections that you get down there, it gets real tough to hear perfect time arrival.

[tomlinmgt]

I am just saying that at those long wavelengths, and with the typical room reflections that you get down there, it gets real tough to hear perfect time arrival.

So when it sometimes sounds to me like the subs are just a little "behind"...bass notes take longer to decay and aren't as articulate...that's not likely a timing issue, per se. I can say with absolute certainly that the majority of the "lag" I heard was eliminated when I changed from a -24 db slope to -48 db.  So that points to a frequency issue rather than a time issue (I guess). Still not sure I grasp phase. Every time I've made phase adjustments at the subs (in a variety of systems and sub locations), it's only made things sound worse.