Kevin, I've understood what you were proposing all along but a) I didn't think you would accomplish your goal and b) I didn't think it would be worth the cost, time and complexity. I am strongly drawn to "simple" and "elegant" solutions and still very much believe point "b" to be true but am willing to reconsider point "a", assuming the conditions I mentioned in my last post are met.

Makes the first round of EQ pointless, because you're EQing each sub under conditions it will never ever be heard in (i.e., by itself). That's like manually EQing the sub flat with the door open, and then closing the door and letting Audyssey EQ it again under the conditions it will actually be heard in. Heck, you don't even know whether some of the settings in the first round of EQing are making things more difficult for the second round.

You say "pointless", I say that I'm giving Audyssey smoother profiles to work with than w/o EQ'ing individually 1st. You say I wouldn't even know if individually EQ'ing 1st is helping or hurting Audyssey's EQ'ing the sum total response, I say, that's why I'd measure to see if there's a difference or not.

What I don't understand is that all 3 of you (Sanjay, Gary, and Gonk) keep trying to argue against this. Have any of you tried this yourselves and know that it won't work? Have any of you seen real test results that show that it cannot work? You're all arguing from a theoretical viewpoint. Gary at least is willing to consider that it could work better. I have convinced myself from a theoretical standpoint that it *could* work better. ... And then I'd measure to confirm that or not.

No you're not. You're EQing each sub flat under conditions that Audyssey will never ever hear. The moment Audyssey fires up both subs together, those individual profiles disappear. You may have pulled down a 6dB peak from one of the subs that would have been acoustically cancelled by interaction from the other sub. So now when Audyssey fires up both subs, it has to deal with a 6dB dip that you created. Of course. Why do you think I keep saying "rather than take my word for it, try it for yourself"? I didn't just wake up one day and decide out of the blue that two subs, each EQ'd flat independently, wouldn't sum to a flat response together. Do you think Audyssey arbitrarily decided to change the way they EQ multiple subs? On the top of the line Denon receivers and pre-pro, Audyssey equalized each of the three subwoofers independently. Denon is planning on upgrading their flagship models to include, amongst other things, the most advanced version of Audyssey that will equalize all three subs together. Do you think such a significant change is based on just theory or real world measurements?

OK Sanjay. Please post your graphs that show that when you EQ'ed two subs individually then the sum total, vs just the sum total, that you got better results with the latter.

In fairness, unless you've tried this with the 2 subs time aligned physically (i.e. equidistant from the listener) or electronically, I don't think you can make that statement categorically. That realization is what made me slightly soften my stance.

It hasn't changed my mind regarding the questionable premise or overall wisdom of what Kevin wants to do, but that's another matter.

Don't have any graphs to post, which is why I keep repeating that folks try it for themselves rather than take my word for it. At least then you'll understand why you got the same response in this thread as you did in the AVS thread you started.

BTW, it was at least 6 years ago when this was demonstrated to me. I had recently gotten the room correction upgrade to my MC-12, when an acoustician friend tried to convince me that I should be running my two subs in dual-mono rather than stereo (when set to dual-mono, the Lex equalizes both subs together). I remained skeptical until he brought over his measuring kit and an outboard equalizer and proved me wrong.

Ack, too late, I already did. Oh well, if Kevin's measurements make me look like a fool then so be it.

BTW, you can do some interesting things by playing with time alignment. If the subs don't have a phase knob, then you can slip the delays to each subwoofer so that their combined responses give you better results (by lining up the peaks and dips from opposing subs to cancel each other out more efficiently). Like when using a pair of subs for modal cancellation, you want one sub out of phase with the other, so time aligning them both correctly would defeat the purpose. Further, adjusting the time alignment of the global subwoofer signal can result in a smoother blend at the crossover region. For example: if you're crossing over at 80Hz, then play a 80Hz signal through the subs and speakers, adjusting the delay of the subwoofer signal till you get max level on your SPL meter (meaning they're in phase).

Finally, the whole "time domain correction" thing should be taken more as marketing than something separate from amplitude domain (frequency response) correction. When you see a peak on an amplitude response measurement, that extra energy comes from sound at that frequency hanging around in the room for a much longer time than other frequencies. If you pull that peak down, you minimize the ringing (which can be verified by checking the impulse response or waterfall graph). If you can smoothen out the response so that you hear all the frequencies at the same level, then no particular sounds will dominate nor mask other sounds, and you'll hear the kind of bass articulation from your subs that "time domain correction" promises to deliver. See page 8 of this white paper.

I'll have to peruse fellow Canuck Floyd's musings over the weekend... too busy today. I'm certainly aware that phase and amplitude issues are hardly mutually exclusive.

Understood. It was just the two diagrams on page 8 that I was pointing to as relevant to this discussion, although the rest of the paper is a useful reference as and when you have the time to digest it. Unfortunately, time domain correction is being marketed as an added feature to consumers that aren't aware that it happens automatically with amplitude domain correction in small rooms.