You can only correct for the response at a single point. And unless all points in coverage are similar, then correcting this single point will not correct the total sound field.
The speaker's directivity alone, which varies as we know, is reason enough for room correction not to work. Not to mention that most of the response from the room isn't minimum phase but varies in both time and strength.
No acoustic problem can be fixed with EQ/DSP unless it's minimum phase. You can't deal with a three dimensional problem using a one dimensional solution.
With Audyssey (in its latest incarnations, such as XT32 at least) you can take measurements in more than just one location, providing a more overall level of room correction that should, at least in theory, be more pleasing to listen to when it’s more than just you in the room listening. If you live alone, or you’re the only person who uses the room to listen to whatever it is, be it music or movies, calibrating from the location where your ears will normally be will end up yielding better results though. I have a higher end Denon with this room correction but I haven’t bothered using it yet since I’m currently only using it in my bedroom occasionally (read very rarely), and since it sounds just fine as it is, I’ve left it alone for now. I don’t think there would be much to gain from room correction in there anyway TBH.
I’ve used Pioneer’s MCACC to great effect however, and I can attest to what a remarkable job it does in taming room response. It does correct for phase, time, distance and it obviously changes the EQ level for each speaker as well. I will say this though, it’s only as good as the room you put it in, and if your room sucks, it can only do so much. Case in point, I moved from one condo to another, both with identical layouts. The first room it was in was roughly 18x15 that had an adjoining dining room, a long hallway, and another small hallway/entry area, so it wasn’t a dedicated theater room by any stretch of the imagination, just a living room. The second room and layout were identical. The first had hardwood floors throughout the entire area, leather couches and chairs, and wooden blinds. The second is carpeted, with a large fabric upholstered sectional couch, and curtains (with blinds as well). In the first condo, room correction through MCACC was able to tame the “liveness” of the room for the most part, but it was less than perfect. In the second room, the results were stunning. It was able to accurately detect the distance of the speakers from the microphone location within a quarter of an inch, and it sounded like a whole new system (for the better), although not a single component had changed, and everything was placed exactly as it was in the other room. Pioneer claims to have developed their MCACC Advanced & Pro in collaboration with AIR Studios in London, and that it’s a 3D calibration. It can tell the size of the room, the ceiling height, the distance of all of the speakers, and adjust for room resonance (again, to a degree, the first room was horrible, but the 2nd was much better and easier for it to “fix”), room modes, delay, phase and more. In the first room, while my Velodyne HGS-18 was “fun”, it never sounded great. In the second room it’s like night and day, especially after running MCACC again. I’ve recently acquired a Velodyne SMS-1 which I plan on using to fine tune the sub even more, but after MCACC alone it’s pretty darn awesome.
I guess my point is twofold, the first being that it’s no longer an attempt to correct a 3 dimensional problem with a one dimensional solution, and that you can correct for response at more than one point. Perhaps when you wrote this that wasn’t possible, you were unaware of it being available, or maybe you’re talking about something different entirely. The second point is that the technology is out there, it’s greatly improved since it first became available, and it does an amazing job at fixing room issues. It can turn a bad room into a tolerable room, a tolerable room into a decent room, a decent room into a good room and a good room into a great room, but it can’t turn a bad room into a great room. It can make a very noticeable improvement, and it’s incredibly easy to use, but like everything it has its limitations. Some rooms need more help than a room correction program can offer, especially very “live” rooms. If your room is good (doesn’t sound like an echo chamber or have too many reflective surfaces), these RC programs can make them sound great!
As far as the original question of messing with anything above the Schroeder line, programs like MCACC and Audyssey are going to do that when they EQ the speakers. I suppose you could save the settings for all the other calibrations such as phase, delay, etc and return all of the EQ settings above 300hz back to flat and see if that sounds better to you, but I have a feeling it won’t. I’m not knowledgeable enough to know exactly how it all works, but if it corrects for resonance in higher registers, and you disable that correction, I can’t imagine it sounding better. Actual room treatments are honestly probably much better than trying to fix a sound issue through EQing, and a room with proper treatments will sound even better after using room correction, but for most people who aren’t highly critical listeners/audiophiles, room correction software is going to be all that they need to make them happy. It doesn’t require panels, bass traps, risers, or isolation, and it’s already built in to the receiver, so why not use it? From my experience it does a fantastic job, and it sounds much better after using it, so why not?
I really don’t know why I would want to make my speakers respond correctly for anechoic conditions. My room isn’t an anechoic chamber, and quite honestly I wouldn’t want it to be. A completely dead flat room is at the other extreme from a super “live” room, and both are not very pleasant in my opinion. In any event, whether or not I wished it were anechoic is irrelevant, it isn’t, and it never will be. I really don’t see how correcting a speaker for a completely different room could be of any advantage to me.
I’ll be honest, I don’t care about the Schroeder line at all. I care about what sounds good, and whatever gets me the best sound is what I’ll use. I understand that you guys like talking science around here, and I do find it pretty interesting, I love science! When I’m watching a movie or listening to music though, I don’t care much about the science, I care about what it sounds like to me. If something makes it sound better, that’s what I want. Room correction software like MCACC & Audyssey work very well, all things considered, and when you combine them with room treatments, they make a huge difference, and can really make a room sound great! I’m all for scientific discoveries though, so hopefully one or more of you guys can figure out a room correction system that’s even better.