Fair question Mark.
Let me put it this way, if you didn't do an A/B test (with vs without screen material in front of a speaker) you probably wouldn't even notice. It is that little. I picked up on it back when I first make my screen frame and put the Seymour XD material on it. Before I mounted it on the wall, I listened to some music with just one M60 plugged in. I then had my daughter hold one end of the screen in front of the speaker, and then lift it out of the way.
Honestly, I may have been noticing it more since I could see the test (screen moving in front of and away from the speaker).
I just let Audyssey handle it. I don't have a SPL meter to test the actual frequency drop, and even if I did I have read several reviews that say that the drop is so small that it falls within the margin of error of the SPL meter, it is THAT little of a difference. The graphs online show that there is no drop until about 6KHz, and then the higher frequencies above that drop a little more the higher you go. Even so, the average dBA drop between the high range of 16KHz - 20Khz is 2dB. Overall average drop is just 0.7 dB. Most professional reviews say that you don't have to make any audio adjustments.
Hope that helps. I guess I am compensating when I don't need to, but why not. It doesn't take that long to do a calibration anyway.
