Hey,
Just wanted to share a bit of experience here.
Before sending back the Senn HD6XX to Drop I made a second comparison with the HD58X, this time using the headphone ouput of a Steinberg UR22 USB audio interface, not the FX-Audio DACX6. According to Julian Krause measurements (
link ) the headphone output of the UR22 is a bit odd especially at low impedances, but it did the job here with enough power regards to the 300 Ohms of HD6XX.
The less bass of the HD6xx was not so disapointing this time, according to Drop's graph it's "only" 2 to 3 dB @ 30 Hz less than the 58x, but the thing that wasn't good is the 5K peak of the HD6xx :
It's a narrow peak but 3 dB above 1 Khz, and it's pretty fatiguing at high-volume listening.
The HD58x is certainly more veiled, less acurate and less "hi-fi" in mids and highs but for sure I can listen to it at pretty high volumes when I want to have fun.
Yet I'm a musician who makes my own piano recordings and I want linear gear to monitor them, but the HD6xx is still too harsh and I stay with the HD58x as an open-back.
The more I try headphones the more I realize I can't cope with any kind of peak above Harman curve.
The Philips Fidelio X2HR follow quite well the target but the very narrow peak at 5 KHz of more than 5 dB is also very fatiguing with metallic sound.
So much well done the job of Sean Olive is, giving us something to target at. In my experience it's clear that's working.
I have the same experience with IEM target, my actual ones are the Moondrop Starfield and/or Aria, they follow very well the target but a bit recessed after 3 KHz according to Crinacle graph and it's very pleasant to listen to.
In similar price range the Etymotic ER2xr is a bit too high in 1 KHz - 3 KHz area and the mids are very "tough" to listen to.
Any IEMs with peaks above Harman curve is also unpleasant to my ears.
The old Diffuse Field or Free Field targets for headphones/IEMs are so much off topic to me, these following it destroy my ears !
Sorry if it's off topic,
c'est la passion !