Pues encantado Yes, AFAIK there are two videos from Josh on the hawks : the initial review, and the halfway complement (75h). I honestly don't believe much in burn-in time (measurements don't show it). I don't want to create yet another endless debate on burn-in, so those who believe in it, good for them, I won't be discussing it. I think it's your brain that's adjusting. Yes, it's weird that it seems to happen so "suddenly". But the hawks definitely like to mess with our brains, by providing a very particular sound that we're not used to. So in the beginning our brain has a hard time finding all the mid & treble info because it's there but recessed, so it has to concentrate. With time, suddenly that concentration becomes more natural, and once the brain learns how to do it effortlessly, then suddenly everything comes up more easily. That could be an explanation. But nobody can tell, really.
We've seen the same videos by Josh then. The one missing is the final one.
I don't have much faith in the burn-in process either. I seem to recall Tyll Hertsens did measure changes in the burn in of an AKG K701. I can't find the original post (it doesn't seem to have been kept in the Stereophile archive) but I think the changes were subtle but noticeable in the measurement graphs.
We're talking a couple of decibels in certain areas, not much but beyond the margin of error of the measurement gear.
But this is not to discuss if it's real or not. My guess certain materials used in the drivers may be more susceptible than others to changes with time and use.
Brain adjustment, though, makes all the sense in the world. To an extent.
We only have one brain (if we're lucky) and many headphones. If brain adjustment was responsible for the added clarity, we would have to experience the same with all our headphones. Given enough time, all of them would feel as if we had applied that famous Sonarworks neutral tuning.
I'm just exaggerating.
Anyway, the NH are very interesting and they have great imaging.