Another aspect that seems independent of frequency response is instrument separation. Some headphones do this better than others. I don't find that a headphone with poor instrument separation sounds better if I turn down the bass or turn up the treble. I mean, yes, I hear more treble then, but that's just making the treble I already heard louder. I can do the same by turning up the volume knob in general.
This is nowhere near the degree of equalisation precision you need to address how different headphones' FR measure at your own eardrum
.
So the answer - for the real world speakers/phones - is "NO", same as expected
None of my EQd phones sounded the same or even really close to another one BUT
the overall tonality (the only thing you can fix with EQ really) was matching well enough
Yep, in practice it's very difficult to do
. I don't think there is any consumer-friendly way to get an idea of what the FR at your drum of two headphones really is like above 800Hz.
Below 800Hz or so it's actually fairly cheap if you're dedicated to learn how to use softwares such as REW and a little bit methodical. You can use simple in-concha electrets such as these ones :
https://www.soundprofessionals.com/cgi-bin/gold/item/SP-TFB-2
This should provide fairly decent
comparative results.
Now you'll have to ask for an acoustician for the exact reason why that's valid but I believe that terms such as "wavelength" would appear in their response. From what I understand at these frequencies the headphones are operating for certain under pressure conditions, ie the measured dB at any point in the volume between your drum and the driver is the same. This is the same principle that's used by ANC headphones with a feedback mechanism.
Above it gets really complicated.
You can purchase this :
https://www.etymotic.com/product/er-7c/
But the sole act of purchasing it is not enough, you'll have to learn how to use it (big problem n°1), and characterise the limits of its accuracy / precision (big problem n°2).
You can make your own DIY version of it (which in some ways is actually better than the original, particularly for measuring headphones as the ER7C's silicone tubing and large microphone housing may pose fitting issues, and in many ways is worse than the ER7C, particularly for questions of absolute values accuracy) :
https://ibb.co/yPC3zDG
Based on a David Griesinger's idea :
http://www.davidgriesinger.com
Jut be warned that this is absolutely not for the unmotivated as you'll encounter a lot of obstacles along the way and you'll need to be quite methodical to properly build, calibrate and operate the probe and characterise what's in your hand to not over-interpret the results you'll be getting.
Measurements done at the entrance of the ear canal with small electrets may also be useful for
comparative evaluations. Most studies on the transfer function between blocked ear canal entrance measurements and measurements near the eardrum show a decent but rarely exact match, and it's difficult to determine whether the remaining differences are tangible or an artefact of the experimental process. Example here, where it matched well for one individual but not superbly well for another (figure 5) :
https://europepmc.org/article/PMC/5992802#free-full-text (that's with speakers though, maybe there are some differences with headphones in that regard).
Personally I use all three methods simultaneously when measuring headphones on my head these days as my confidence in each of them depends on the area of the spectrum.
In most circumstances it's probably still a better idea to start with something that you already enjoy and fine-tune it. I am skeptical that the Sony MDRZX110 is a good starting point for most of us
.
