The danger with that is I might end up shaving the beard and slicing sub optimal bits of ear off in pursuit of better measurements
Well, it's actually something practically you would do for a better
listening experience.
As I mentioned, you may end up with much less bass compared to the average (Harman or any other target) just because of bad sealing properties. Without knowing one could be fooled into believing that he or she is an absolute basshead ...
this really looks interesting! though with this system without a proper head simulation shape (for the head transfer function?) it might varies a bit with actual person. but then it should provide us with a sense of how a great measuring speaker in the listening position with the room measured FR and then compare that to the headphone measurement system, so we will know how well that fit into the Harman curve or not?
The Harman target does already include an HRTF model. They used a dummy head (with their ear simulator inserted) to record the in-room response at the listening position.
Nobody has mentioned soundstage, image, or imaging in this thread, but it often occurs when someone asks about the user experience, as one of the "characteristics".
I'm afraid that we do not have the approriate standards and technical requirements to capture such
highly individual phenomenons, yet.
... not the newer RA0402 'hi-res' coupler. The latter could result in not only less accurate results for preference ratings, but less accurate EQing to the Harman target too, and the difference is not insignificant, with potentially audible-level differences when EQing in the treble from around 6kHz up, with a 6dB difference at 10kHz:
Using the RA0402 hi-res coupler for measurements could then result in falsely EQing the treble up to 6dB too hot when aiming for the Harman target (in addition to lowering the 0.86 / 0.91 correlation of the calculated preference ratings using such measurements).
That is on of the many evidences showing that there is not
a truth but
thousands of varied interpretations of what could / should / is clamed to be the truth.
Also, the term "accuracy" is only considered in relation to a controlled test system with a standardized fixture. As soon as you vary the contact face and the size and shape of the pinna and ear canal (in short:
introduce human factors) the whole thing will collapse into a grey area of uncertainty. Measuring frequency responses with a standardized ear simulator
can be a completely different thing than the actual listening experience as soon as the anatomy of the individual deviates from the test fixture.
As for the coupler / ear simulator resonances, keep in mind that the data shared by GRAS do only reflect the measurements of IEM,
which makes the system a closed tube resonator!
For circumaural headphones you have to calculate the resonances for an
open tube with much longer wavelengths (10 mm of coupler tube + ear canal + lateral concha gain). The higher the wavelengths, the lower the frequency of the modes - which will introduce much deeper resonances in practice than those specified by GRAS for the closed resonator case!
The Acoustics of Hearing Aids: Standing Waves, Damping, and Flared Tubes
Unfortunately, there is no satisfying conclusion for such phenomens. The resonances may shift in both level and frequency depending on the length, diameter and shape of the ear canal.
IMO both the old and new 711 / 60318-4 are wrong because they suggest a somewhat completed science that is able to address all the individual factors. The newer one is smoother, indeed. But not necessarily more accurate. But then again ... what is even "accuracy"?
- The IE target curve was developed using a G.R.A.S. RA0045 IEC60318-4 compliant coupler. Other common fixtures for testing IE headphones such as B&K 4128, B&K 5218, G.R.A.S. KEMAR, etc. have not been validated against the target and may not produce results that correlate 100% to the predictive model.
- The AE/OE target curve was developed using a G.R.A.S. 45CA headphone test fixture with a custom pinna. Other common fixtures for testing AE/OE headphones such as B&K 4128, B&K 5218, G.R.A.S. KEMAR, etc. have not been validated against the target and may not produce results that correlate 100% to the predictive model.
I am pretty sure that they confirmed and recalibrated their findings after the release of the newer "high-res" simulator. However, with that much smoothing applied I would consider the differences to be rather negligible anyway.
As for the pinna, they mentioned that they adopted the newer anthropometric model right at the time where Welti experimented with the sealing properties of the old and stiff IEC pinna which was actually developed for hearing aids.
Regards
Dreyfus