I think it does mean something since we already know it's not linear. If it was linear there would be no FR change for my 8 vs 10mm tube, just a drop in level. Also what I mentioned in my reply in the Andromeda thread. For full disclosure, here's the data (mind this is only 3 IEMs) I referred to. We would think the FR difference between a simple tube coupler and an IEC 711 coupler would be something like this: When averaging the three IEMs, I got this: Which is somewhat close considering I didn't match the insertion depth and didn't use a microphone compensation. Also I think it's an expected result since the input impedance of the 711 coupler really only has that characteristic "step" from 1-2kHz in it, where the eardrum transitions from stiffness controlled to mass controlled (see above B&K study from G.R.). However looking at the individual IEMs we see this: I would disregard the data from 4kHz on since I didn't match the insertion depth. With three IEMs it's hard to say. I'm not really sure if we can see anything here. But the 711 coupler does seem to show slightly more bass with both DD IEMs relative to the BA UERM FWIW*. B&K 5128 likely even more so given the above measurements. I could include my ADDIEM measurement, but that's about it. You've probably measured more IEMs that we have 711 measurements of than I have. *Note that for generating the difference I only took Rin's bassy left channel UERM custom measurement. It seemed to me he didn't get a good seal with the right channel. Using an average of L&R or using his universal sample measurement, the difference would be much greater.