So do you think there's some other advantage Stax headphones have (if so, what) or do you dispute that they're better?
I'm not an acoustician so I don't know. All I know is that quite frequently when another factor than frequency response is proposed as the cause for what someone hears, counter-examples aren't too hard to find (THD is an example).
And since frequency response
at a specific listener's eardrum (and it might vary across listeners particularly at the two extremes) remains a
very uncontrolled variable, it's probably there that the answer should be looked into first IMO - ie is there something with Stax' headphones that makes them more likely to deliver an FR curve at the listener's eardrum with some specific features that some people would consider desirable ?
For example, from what I understand the idea behind Rtings' PRTF measurement is that they made the hypothesis that some headphones interact with our pinna in a more "speaker-like" manner which could potentially enable them to produce an FR curve at a specific listener's eardrum that better matches what the listener's anatomy makes him / her expect to hear (provided the basal FR curve is correct). In another word that the variance at listeners' eardrums would match better with some headphones the variance we see at their eardrum when listening to speakers.
This is the sort of information for which measuring headphones on a HATS may not quite provide.
Measuring FR curve at listener's eardrums is a royal PITA and requires quite a bit of kit apparently (
https://www.etymotic.com/auditory-research/microphones/er-7c.html) - and more importantly probably quite a good deal of know-how to start with. There's that paper for example, but there aren't that many to start with :
https://www.aes.org/e-lib/browse.cfm?elib=16877
I wouldn't be surprised to learn that companies working in surround sound simulations for headphones are increasingly gathering this sort of data
en masse combined with 3D scans of the listeners' ears and their HRTF.
Now this is just me, but the more I'm learning how to effectively EQ headphones in a way that I hope increasingly corresponds well to my anatomy
, the more I'm subscribing to the "let's look at FR
at a specific listener's eardrum first and the rest second" crowd.
I've never listened to Stax' round headphones, but I've owned their SR507 for a few years. Didn't keep them. I never thought of them as magical, just different in an interesting way.
As mentioned earlier, I have heard about "speed" but not sure whether/ to what extent this is a scientific rather than an audiophile concept.
It doesn't have an operational definition, so we can't apply any form of scientific method to test for it for a start.