Did you see the video links?
It is measured
And as I showed you, I measured no significant differences between two firmwares that span wider than the firmwares Aaron compared. So which one should you follow ?
I will also add that since Aaron seems to find a change in FR with nearly every APP2 firmware Apple released, and often varying up and down per frequency, or between the lighting and USB-C versions, in a completely random way (but mainly within a specific part of the spectrum, ie 600-4kHz), Apple must be complete lunatics if they were constantly tweaking the response in that range in such a way.
What you're seeing with Aaron's measurements is most likely down to a) use of a measurement device that's not ideal for a start (even 711 couplers, clones or genuine GRAS or B&K ones, aren't entirely ideal IMO), b) not using the right procedure to measure them, c) at higher frequencies (6kHz +), a different seating or set of seatings.
So nope, his measurements are no evidence that firmware updates altered the FR.
So you are saying Apple (or Sony or Samsung or Jabra) do (or did) not change the sound via firmware update?
What I'll say is that I found no evidence of a change via firmware update in a 711 clone coupler between the firmwares I measured, when the APP2 is measured according to the right process (which, if you're going to use a sweep to measure it, needs to be properly primed beforehand).
But I think that it's a good deal more complicated than that. Apple monitors the in situ response continuously and modify the response in real time up to around 4kHz, and between around 600-4kHz seems to require a broad signal to reach a stable response (it's not a straightforward ANC feedback system that they're using, and while I think that I am starting to understand some of its behaviour, I'd still like to learn more about it). I am sympathetic to the idea that they refined the way the adaptive algorithms work - I personally experienced what I'd consider a somewhat unstable response and ANC performance with early firmwares (ex :
https://audiosciencereview.com/forum/index.php?threads/airpods-pro-2.37164/post-1349127) -, and that to a given individual this may have resulted in a change over time, but there's just no evidence for it other than subjective impressions (including my own), and I don't think that it's ever been meant to change the
intended tuning but rather to deliver it more reliably.