General Measurement Notes for IEMs. Resonant peaks from 8kHz to 13kHz could be measurement artifacts caused by the coupler. Take anything after 8-9kHz with a grain of salt because of the limitations of the coupler. The coupler rolls off massively after 14kHz. There is no attempt to compensate for this. For impedance measurements: there is a 20 degree phase shift at 20kHz (starting at 10kHz) and about a 10% impedance roll off at 20Hz (starting at 50Hz) inherent with the impedance measurement apparatus. Also the impedance measurements might be off by a few percent. When I have more time, I'll build a proper system for this measurement; but the current results should still give us the gist of things. 0db on the frequency response chart equates to 105-100db SPL. The distortion measurements are per the levels recorded for the frequency response. IMO, there should be a slight bump aroud 2-3kHz because we are bypassing the pinna with IEMs. The pinna tends to elevate this area. 26 May 2016 I'm in the middle of updating the IEM measurements. Some measurements I redid to get clearer distortion results in the bass. I'm also compressing the Y scale from a 100db range to 70db to make frequency response differences more apparent. There are also some very minor tweaks to the compensations. 23 August 2016 Note all IEM distortion measurements plots up to now 8/23/16 have been removed from the body of the posts. I've put a placeholder [DEFUNCT] in their place. Meaning no longer existing or no longer functioning. In the meantime, I will be retaking measurements of IEMs I still have around and will be posting better distortion measurements that make A LOT more sense. In some instances, the FR will be slightly different with less roll-off in the bass and smoother 2-3k and last octave bumps. There will also be slightly more differentiation in these areas. But not different enough so we can't compare. A big thanks to @Serious for his analysis and his ears. For those who have been around since the CS days, these kinds of changes and tweaks are normal, particularly when we break new ground - in this case IEM measurements. I'm just glad that a few of you caught some of these things before we had too many measurement to redo. Sometimes it takes a critical mass of measurements to build up enough data to analyze.