I'd like to think that I've listened to quite a bit of those, at various price points, and I won't follow you there
. For one simple reason : frequency response
at your (or mine !) eardrum remains an uncontrolled variable beyond threshold of audibility in all likelihood.
It's most likely that you've never really heard what is a "textbook" Harman tuned headphones, because the frequency response on headphones at your own drum is very, very likely to vary at least a little bit (enough to be audible) from measurements on artificial ears - and the latters aren't always in agreement beyond threshold of audibility to begin with
(the AirPods Max is a prime example of that past 800Hz).
This is nothing really new :
https://www.aes.org/e-lib/browse.cfm?elib=16877
This has been one of the impetus behind my attempts at measuring my headphones on my own head with various devices and characterising how representative they are of the actual output at my drum :
https://www.head-fi.org/threads/how...guarantee-a-better-sound.958201/post-16405751
Using the probe above, this is an illustration of the actual response of my samples of the HD560S (orange), HD650 (blue), Hi-X65 (purple) and K371 (green) on my own head (right ear). Above traces are with no EQ, bottom traces with Oratory1990's Harman EQ preset applied.
View attachment 140814
Please don't over-interpret these measurements, they have their limitations (cf. link above). Mainly focus on the
relative differences between headphones and don't look at numbers in a dogmatically exact way. You can't say "at 8548Hz headphones A is 5.67dB louder than headphones B when normalised at 347Hz", but rather "at around 7500Hz, headphones A
tends to be 3-3.5dB louder than headphones B". I'm I the process of eliminating a number of concerns I have about this methodology by comparing this probe's measurements with blocked ear canals measurements at the canal's entrance and while I'm not certain that I can find a
single constant transfer function between the two methods for
all headphones (particularly above 7kHz), at least below the "different differences" between the two methods seem to have identifiable causes (mainly related to the blocked ear canal) which is reassuring me about the results I'm getting so far.
Also note that the K371's results are less reliable than the other three as it's got quite a bit more seatings to seatings variation.
Results ? While Oratory1990's profiles helped in coalescing the curves together when looking at them with a lot of smoothing, there are still audible differences, whether in terms of large bandwidth "tilt" of the response or in terms of fairly high magnitude, narrow bandwidth peaks / dips, both above the typical tolerances I tend to allow for with this measurement process.
The question then becomes : which one is the most representative of the Harman target ? It's actually probably a moot point as an individual can't really know, since HPs will invariably vary at least a little bit on your own head. We can have a general idea of it, but not a particularly exact one I think.
More interesting IMO is to ask : which one is the most representative
for you of Harman's research
intent, ie reproducing "good loudspeakers in a good room" - which is something that will necessarily vary a little bit from what is measured on a HATS as your own anatomy differs from it
to some degree.
Degree is in my opinion the key word here. It's not
that high that it makes Harman's research predictive value invalid, or justifies rubbish FR responses such as this one :
https://www.rtings.com/headphones/1-4/graph#1619/4011
But it's probably high enough that it's audible, and makes Harman's research predictive value fall apart once two headphones are measuring close to each others to begin with, or close to the target (ex : HD600 vs HD560S).
Ie to the question "what is the probability you will prefer headphones A over B ?", I think that the probability would in all likelihood be quite high if headphones A is Harman tuned to begin with vs., let's say, the monstrosity above, less so if headphones A is the HD600 and B the HD560S.
There is ! Particularly for THD I believe.
"What we mean" is a question for terminologists, but I'm not sure that it's of that much value for acousticians
.
In any way it's a bit of a moot point if FR can't be a controlled variable below threshold of audibility.
"Soundstage" might actually be one of the most operationally definable terms in the list above, as "true" soundstage may be tested, for example, using object based rendering formats / engines (let's say an FPS game with such format) and generic or personalised HRTF profiles, and asking people to properly aim at a target blindfolded for example (or even better move in a virtual 3D space to the location of the sound source), and score them.
With the usual stereo music recordings played through headphones it's probably not such a meaningful term as they necessarily lack some of the components that help us locate sounds in space.