@Muse Wanderer came over for a listen today after High End and brought his Utopia and Andromeda with him, for me to give a 2nd listen and also take measurements. This is also the thread where I wanted to continue the discussion that @k.e. started in the Andromeda thread. First up, here are the standardized measurements of UERM and Andromeda on an 8mm inner diameter tube that was calibrated to match the IEC type couplers. Referenced to about 2.83Vrms. Keep in mind that insertion depth and ear canal size play an important role in the resultant FR and sensitivity. The channel imbalance with the UERM is the effect of a slightly different insertion depth and I mainly did that to show the effect of the insertion depth. Even with customs there's a bit of room for different insertion depths. It's harder to get a good seal with customs, so bass extension might even be better than this. Subjectively I prefer the UERM bass. The Andromeda seems to be about 11db more sensitive at 100Hz, but considering a 4 Ohm impedance for the Andromeda and a 50 Ohm impedance for the UERM at that frequency, they are both almost exactly the same efficiency. The answer is it depends. With my own measurements I look at the raw, uncompensated measurements and I use a compensation curve to get the measurements to look like the IEC measurements. With the IEC measurements I basically use the compensation curve as a target. There is a difference between ear-canal opening measurements and measurements with the microphone at the eardrum level and it's not just the ear canal. So no, the HD600 shouldn't show a 10db bump at 3.5kHz, at least not with that type of measurement. True, but overall I like to think that IEMs don't have random parts to decrease efficiency in them for no reason. If the parts serve to better achieve a target FR then that's fair, but should definitely be factored into the efficiency calculation. The correlation with sound quality doesn't have to be perfect. The Andromeda sounded far too bassy from a near 0 OI source for my tastes. It was almost perfect from the Ragnarok SE out, but you have to use low gain to avoid hiss. Here's the Andromeda FR from the Ragnarok SE output (3.3 Ohm): Three key differences: Andromeda has less energy in the fundamentals region around 500Hz. This adds more thickness to the lower mids. Andromeda has more energy in the 1.5kHz range. This might not be a bad thing. Andromeda has less energy in the lower treble around 6kHz. This can be good or bad depending on your preferences. I also attached a comparison between the 3.3 Ohm and 0 Ohm measurement. Subjectively the UERM bass still sounds clearer (but not as clean as HD800 or my speakers) and the UERM is also less closed-in.