I've started measuring my HPs with DIY tube mics in my ear canal. While I don't really want to present this as a paragon of absolute exactitude, quite far from it, it's actually starting to be fairly reliable (around 0.5d-1B in variation ? Something of this kind) for
comparative measurements during the same measurement session (ie when the probe isn't moved) -
and of course it's only valid for my own samples, on my own head :
https://www.head-fi.org/threads/how...guarantee-a-better-sound.958201/post-16405751
My own measurements this way are way better aligned with my subjective impressions of the APM than what I see online from test rigs. If I apply EQ based on the latter to my APM they just sound completely off (way too much energy for me in the ear canal gain region, for obvious reasons since most of them show a pretty significant deficit in that area).
View attachment 136982
Right channel only, average of 5 reseats each. APM in green, K371 in purple, HD650 (with somewhat fresh-ish pads) in blue, HD560S in red.
Note that I'm not quite as confident with my APM and K371 results as with the HD650 and HD560S. For the latter two the relative difference between the two has been repeated in at least four, five sessions, some weeks apart, while for the K371 / APM only two sessions.
I'm not sure of this at all, but experimenting with clamping force and the spring loaded cups makes me think that the APM's specific design may not work superbly well with some test rigs.
So I actually think that it's pretty decent for a closed back in terms of FR -
at least on my own head -, and I actually prefer it to my K371. Bonus is that it's way more consistent because of Adaptive EQ at lower frequencies (and given the rather smooth FR up to 4-5kHz it's quite EQable), while my K371 measurably varies just by leaning forwards... and so far channel matching is quite excellent (since the acoustic design is nearly fully symmetrical front to back it's one of the few headphones you can reverse and still get valid results when measured on your own head). I've also had two copies at home for one of these sessions and they both measured quite similarly.
So back to your question, IMO that's not the best example around, because it isn't
that bad in terms of FR - well at least on my head
.