Hi Crinacle, thanks for clarifying. The 5-6 Khz is an especially sensitive area for human hearing, as it easily tends to harshness. It is also one of the regions that responds the most to burn in. I mentioned the Solar before, and the Flamenco, but it is also the case with SPC and silver cables. Of course, if you don't believe in burn or cables this is all a moot point.
There is a reason that reviewers as average_joe, MikePortnoy, twister6, and myself always burn an iem for 100 hours before doing critical listening, so the sound impression is not affected. It is a courtesy to the manufacturer, as sometimes the sound might be affected, and sometimes not. In the case of the W900, I found the difference quite large. The loose bass resulted in a warm signature that resembled a more midforward signature, while the stage was particularly warm and lacked airiness, even up to 50 hours. At 100 hours, the bass is controlled, resulting in a more neutral signature and clean stage.
In the case of Flamenco the energy of the 6 KHz is more prominent at first, which not only affects the tone, but the prominence of the lower midrange. In the case of the Solar's 6 KHz peak, it tended to be sharper and more sibilant at first. I don't know if it will show up on a freq graph. I find frequency graphs very interesting, but they are a very unidimensional representation of sound, that hardly reflect the whole picture. Sometimes there are graphs of iems that look identical, but sound very different. In the case of the Flamenco graph you show, there is a heavy rolloff after 4 KHz. The 6 Khz peak should be at least as high as the 2-3 KHz peak. The frequencies after roll off even steeper. To me, this does not inspire confidence that it would be able to pick up a sensitive change. Maybe a 15K setup might, or a CSD graph reflecting the time decay of energy. I trust my ears. If you want to put your faith in this specific measuring setup, that's fine by me.
I'm not really interested in a burn in/measurement discussion. It's ok if people have different opinions, and I lost interest in getting riled up over them. Like I said, overall you wrote a good review, and it is not my intention to downplay that.
