Originally Posted by curttard
Is Audyssey MultEQ XT32 so magical that it can correct for two subwoofers of different make, model, and performance? Or would I be better off sticking with just one?
Yes and no.
MultEQ XT32 (or more accurately, along with SubEQ HT) doesn't know or care what make and model your subs are. It will take the two subwoofers, time align and level match them so they are contributing equally to the output and in phase with each other, and then create an EQ filter to make the summed response of the two subwoofers as flat as possible. It is really, really good at this.
However, what it doesn't do is measure the "performance envelope" of each sub to determine what the respective capabilities are. The level match step is blind to performance characteristics. And the level of the test pings (75dB or so) isn't anywhere near loud enough to strain a subwoofer to its limits. It just pings the subs together and flattens the combined bass response. So it's not magical enough to be able to determine that one sub is much better than the second sub, and optimize things accordingly.
So it's possible, if you have two subs of vastly different performance, that when you crank up the volume in real world usage that one sub will poop out before the other does. Technically, even if you had identical subs this could be possible too due to room acoustics / distance differences. With room / distance effects the exact same sub, set to the exact same gain, could be asked to provide significantly more output in one location vs another. For example in my room, when I place the sub on the left side (nearer the corner) vs the right side (more in the middle of the room) I get about 10-15dB of "free" bass from reinforcement between 35-70Hz or so. And thus the same exact sub, set at the same exact gain, requires a lot less trim from the receiver on one side vs the other.
But this is getting into the weeds and in the "real world" probably not a concern unless you are really pushing the system towards its limits.
So I would say that as long as your subs are close enough in performance, I wouldn't worry about it. If they are drastically different in performance, I probably would worry about. You can mitigate differences by being clever (e.g. placing the less capable sub nearfield, and the more capable sub further away, so that the level match naturally makes the better sub work harder). Or if you have measurement gear you can optimize placement objectively.
All that said, I would NOT go down to one sub if you have two. The benefits of multiple subs are significant in smoothing out the bass response across the listening area and cancelling out room modes.