Except MCACC doesn't do any equalization on the sub channel (from what I've been told. finding direct info from Pioneer on this has been problematic), and none of the advanced MCACC frequency points are below 60hz if memory serves. So if I throw the sub out of phase it won't do a thing to it to remedy any cancellation.

Anyway, they are in phase at the current crossover point based on the cancellation I saw. And it was indeed cancellation. When I saw that db drop on the second pass at 180 degrees, I turned off the sub and it almost entirely went away (not totally because the Sierra's and the sub work in concert to keep things relatively flat normally... so no sub = less net output).

As for running mains full range with a sub... why wouldn't you do it? If a main starts naturally rolling off at frequency X, what's the issue with asking another speaker to step in below X to keep the response going? I'm not saying I run it with the sub playing up where the Sierra's already have things covered. I'm not running some 12-24db bump overlap in the 40-50hz passband.


Anyway, we're now talking about three different points at the same time. I confuse easily.

1. Low crossover of subwoofer due to localization.

I've tested this six ways to Sunday at every crossover point I have available to me from 80hz on down on two different sets of main speakers over the past year. I tolerated it at 50hz cause my old speaks would peter out by the high 40's completely, so I had to put them on a 50hz highpass to keep them safe. Sierra's roll down into the low 40's just fine at the listening position, and the sub props things up the rest of the way.

2. Phase issues at a crossover point.

See response on point one. I messed with phase at every point of the way a year ago when I did this. I didn't really see a point of going through that mess again. I tested localization the day the Sierra's showeed up, both at 80hz and 50hz. I could localize. Evaluated how low the Sierra's could go, set the sub accordingly.

3. Running mains full range + sub.

I don't see the issue with doing this. What am I missing?