If I understand correctly, the measuring of LF waves is challenging, thus inconsistent. For example, when starting Audyssey tests, you begin with the Subwoofer SPL screen where you have to try to dial your gain in to about 73dB. Isn't that fun watching the OSD of your Sub SPL jumping all over the place while making that adjustment?
I know the Aud mic isn't the best tool in the workshop, but it's a good start.
Getting Audyssey set, with levels and distances is useful. Though I don't have studies to back it up, my XT32 App usage has always seems more consistent from test to test than just using the AVR did. Ultimately, it would be nice to check the timing of delays set by Aud, as this seems to be one of the more misunderstood aspects of dealing with Subwoofer DSP and "Distance" settings. (Consider the general rule of thumb that gets tossed about; that the distance for a Sub could be anywhere from 1/2-again as far to twice the actual distance-to said Sub!)
Some intense critical listening sessions always accompany my playing with Auddyssey. Can I hear a difference? Better/worse? Is that 2K-5K Hz range too bright still?
Does the bass sound tight and distinct? (I'm not suggesting I can hear the difference of a msec in delay, but I do know the App dialed in my subs better than just the receiver.)
Regardless, the other comment I wanted to chime in on is the dreaded MRC. I experimented with that early on because my room is pretty bare and those frequencies were definitely strong in my room. I used it On, Off, and even drew in my own version of MRC for a bit using the App. For that, I made the dip shallower and wider: more of a gentle swale only 1.5dB deep rather than a 3dB crater.
I actually found this to be a very pleasing solution to my room for a while until I got better positioning locked in.
Using REW or OmniMic is a definite necessity to take Audyssey to the next level. We've seen time and again the progress friends have made with further dialing in their subs and flattening their FR down below the Schroeder Frequency of their room.
Which brings the last point: setting the Frequency Limit or Curtain for Audyssey correction. When your room transitions from acting as a resonant chamber to more linear performance, that is the Schroeder Frequency. Numbers I've seen tossed about range from 100Hz up to 500Hz. Most commonly, I think it tends to fall between 200-300Hz in most domestic rooms.
I use the before graphs for my Subs and Mains in the Aud App to eyeball the point where the FR starts to naturally even out and set my Curtain there. No need to correct above that point.
This is a simple introduction with links to 2 S&V articles by BB... good read!:
Brent Butterworth, a writer over at Sound & Vision, has written a very easy to understand explanation of what the 'Schroeder' frequency is. The Schroeder or 'transition' frequency is a critical concept to understand because it explains a lot about how sound behaves in rooms, how we measure /...
www.acousticfrontiers.com