Great to meet
@McMadface at CanJam
But sad we had so little time
I spent all of about 5 minutes rushing through the measurements of the MH755. I hope I did it justice.
Welcome to the group
@oratory1990!
A few things for us to consider...
As
@McMadface mentioned,
@jude has graciously agreed to join the tour, but as anticipated, he's swamped right now and won't be able to get to this until end of July at the earliest (after CanJam London). The good news there is that gives us plenty of time for
@antdroid to do some measurements and maybe even for us to find somebody else on this side of the pond to join the tour before we mail these IEMs off to headfi HQ and then Europe. (
@SilverEars - you interested in joining?)
I mentioned to
@McMadface that GRAS have kindly offered to loan me an RA0402 "hi-res" coupler to test out. This is a couple of weeks away, but I'll probably take them up on the offer. Maybe I can schedule this after
@jude has done his measurements and that way he won't be on the hook for the international shipping fees to Europe. These hi-res couplers are certainly interesting, but I'm a little concerned about the fragmentation of standards. The RA0402/0401 is supposed to be backwardly compatible upto 10 kHz, but from what I've seen, it's not. It adds a very strong (14 dB) attenuation to the half-wave resonance which can affects peaks near 10 kHz and can affect THD down as low as 3 kHz.
@jude mentioned something very interesting to us at CanJam, which is that Brüel & Kjaer are coming out with their own "hi-res" coupler, which will (of course!) be different again from the GRAS "hi-res" coupler. The B&K version will apparently be good up to 24 kHz and is based on medical imaging scans of 40 Scandinavians (Danes, I believe?) and so likely to be more representative of a true average of the human ear anatomy than the (seemingly random) decision of GRAS to damp a resonance mode that is insertion-depth dependent. The problem then is we'll have vinyl-tube couplers, 711 couplers, GRAS hi-res couplers, B&K hi-res couplers, and an almost certain guarantee that no two measurements in the world will ever agree again. Dan Clark (Mr. Speakers) made a comment at the CanJam AMA that every current measurement rig gives different results. Another depressing fact - even the GRAS RA0402/0401 only specify an accuracy of +/-2.2 dB, which could be fairly significant in comparing measurements from different rigs, even when using the same equipment and measuring the same headphone unit. As a result of all this, I have some thoughts, suggestions, questions, requests, etc., about how we might proceed with all this.
Somehow we have to make our measurement data available to one another. Some of us may end up using different couplers with different impedance/Q-values and resonant volumes so we can't guarantee a perfect match to every other headphone, but a solid starting point would be if we each supplied the data on these two sets of IEMs (ER2SE and MH755). This way, any one of us could match their results (at least to an average of these target headphones) to those of anybody else in the group. I think the easiest way to do that would be to simply have everybody upload their measurements. I think individual posts on this forum would be the best place to host these data files and then I can simply link to them in one big indexed list from the first post. I like REW, but others may be using ARTA or something different entirely (
@McMadface suggested Excel format). We could perhaps let a users' preferred format be discretionary, but also mandate a universal format that everybody can read, such as simple 2 or 3-column ASCII, uploaded in a post that contains a description of the measurement rig used.
In an ideal world, I think we'd all want to ensure the following:
1) That we've all used a common, or similar, SPL for measuring. (I typically use 95 dB for FR and 80 dB for THD.) This is probably not critical for FR, but some headphones' FR shifts a bit with SPL.
2) That we've either performed a loopback-calibration for our driver/input sound-card/analyzer combo, or confirmed that both input and output are ruler-flat (i.e., confirmed that we don't need one).
3) That our source driver has a sufficiently-low output impedance that it isn't skewing the recorded frequency response. This shouldn't be an issue for the ER2SE or MH755, but it could be for other IEMs.
4) I don't think any of us need to see anybody else's sound-card calibration files, but it might be interesting to see any mic calibration files used (or to upload both uncompensated and compensated data), to see how much of a nudge that particular coupler/mic combo required to produce the final measurements. (Because we know we can all perfectly match anybody else's data with a suitable compensation curve.)
Does it even make sense to try and converge on a reference target FR for our final measurements? We could try to define one as some giant average of all our measurements, but on the other hand, it's unlikely our target measurements are going to form the basis of any new international headphone measurement standard
Thoughts?
P.S. Sorry
@castleofargh - you got bumped even further down the queue. And with no foxy young chicks to show for it
the only time I feel that dumb is when I tweak my EQ by a tiny amount, just to notice later that it's bypassed. something that happened to me way too often for my self esteem to be fine. 
. 