This is looking to be a bit more straightforward than anticipated, though that doesn't mean easy answers, lol. The coupler seems to be performing well.
After correcting for this:
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Genuine GRAS couplers may not always be aligned with the centre line between the standard's limits :
For the few select IEMs which I own that I think are appropriate to perform this first line of checks, the average delta that I obtain vs Oratory and CSGlinux's databases is not exactly consistent with correcting the transfer impedance plot that was provided so that it aligns with the centre line, but I think that as far as I'm concerned the sample size is still too small to begin with.
I get a good, consistent matches with oratory1990 (of results that more or less have the 8kHz resonance line up and which seem to be more recent).
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Looking good so far ! If you have a deeper insertion IEM (ER2SE for example), it could be interesting to see how it compares as well - but in the case of the ER2SE seatings can occasionally be quite inconsistent when using the older-style tri-flange tips and sample variation isn't perfect either. Don't over-sweat the details, even comparing Oratory and CSGLinux's databases does not result in a perfectly flat transfer function.
I've been quite happy with the sample variation of the Moondrop Chu (1st gen) so perhaps add this one to your roster of test IEMs :
(this is each earbud compared to the dB average of all six.)
You may have noticed that the resonance may be slightly less dampened in your coupler out of the box. I would try to experiment with damping material (which you can place for now right behind the reference plane, above the protective grid). I would not try to compensate with a static compensation for damping issues.
It seems from comparing 3 different IEMs (and multiple copies of each) that the only important difference between these RA0045-based results and Amir's results (outside of the resonances, obviously) is this, roughly a 1.5 dB bump between 800-5kHz.
That's the general trend I observed as well, with differences above as well in terms of damping / length modes and some additional factors.
Again, I am shocked by the consistency I am seeing. I thought the coupler was going to be a piece of crap, honestly.
Some are for the most part quite fine in terms of acoustic impedance indeed. The problem has never been that they're always sh*t, it's that they vary .
Ironically, this seems like the opposite of what one of the graphs in the thread described.
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That's just RA0045 vs RA0402, the pinna is not involved here.
I have always had the suspicion that IEMs were brighter than what many results show.
I am not certain what you mean by "brighter", but 711 couplers are a bit less accurate than newer type 4.3/4.4 ones in terms of representing the average acoustic impedance. The transfer function between 711 couplers and the 5128 tends to tilt the midrange brighter (here four different sources doing the same test, that is to say compare a bunch of IEMs on a 5128 fixture and a 711 coupler, and plotting the difference) :
Your own ear's acoustic impedance may not necessarily align with the average however.