I really know next to nothing about this subject, but it does seem to have some possible merit. As I said, I really don't know what I am talking about, but I am interested in this subject, so don't rip me too big of a new one! LOL! Also, maybe I'm deaf, but I could not hear any difference between the first set of low gain clips, but I could hear a slight difference in the high-gain clips.
I was looking at frequency responses of speakers (although they were near field monitors which are meant to be flat) and saw some discrepancies between lower output levels and higher output levels.
It was in this article:
ESI nEar 05 eXperience Active Studio Near-Field Monitors
Although I realize that this is a completely different beast, perhaps this is relevant to guitar speakers as well. Since IRs seem to me as though they are simply spectrum analyses in the form of a spectrograph, then it seems as though perhaps a spectrogram could be used with the third axis being that of volume or dB or output (I really don't know what the term is).
As I say, I really don't know much at all about this subject, so I could be talking out of my *ss, but perhaps it is something like that, and possibly the differences are more pronounced in guitar speakers. Even if it is not all that obvious, there may be some merit, as people seem to have very sensitive ears and hear things that I can't. I just think it is an interesting topic, and being kinda nerdy, I like to think about such subjects, so be gentle when you tear me apart!
Thanks for the explanations of motor drive and speaker drive, Cliff. Maybe these are what the OP article are discussing in all actuality, and perhaps that is what is happening in the article I read.
This forum is awesome, because we can actually receive responses from the engineer of the Axe and we can discuss the craziest, off-the-wall stuff.