@grump
RMAAs with an IEM as load don't have the same purpose, they initially were a simple method to assess if the impedance of the DAP was high or not. like the guys at ABI were doing some years back using the triple fi on purpose because it would make a mess of the FR if the source wasn't low impedance. the IEM had a huge impedance swing going as low at 8ohm. and that was exactly the reason why it was used. incidentally it also often would show if capacitors were at the output and creating a high pass with the IEM. so it felt like it answered several questions in a simple free test.
now to actually measure the DAP itself, instead of the impact on the FR with a specific IEM, I totally agree that a resistor is what should be used. BTW question to anybody who knows. I have plenty of cheap crap resistors(you know the "buy one, get 1000free" kind of crap), but I get in trouble with some when I run something several times for averaging. some resistors clearly change behavior when they get hot. is it because I really use the crappiest crap that exists, or are there resistors better than others for such tests? if they're expensive stuff, forget it I'm a cheap bstard when it comes to measurement rig. but if not, I could most certainly improve the accuracy of some of my pikatchu tests. with one or 2 proper loads.
what interests me with low impedance loads is that instead of looking at fullscale voltage and almost no current, we see how the amp behaves when it's actually difficult. higher current flow, worst crosstalk, things getting hot, more noise, can it even provide the current for the load? all of it becomes fun into low impedance. that's where we really find the limit that interests IEMs users because indeed IEMs nowadays often have very low impedance at least at some frequencies.
and about microphone, maybe it's me that confused everybody, I mentioned it to say it's not a good idea. it's obviously not the best idea for people used to doing those stuff, but it's usually the first idea people who know nothing about measurements will have. you want to know the FR of a system, measure the sound getting out of the entire system with microphone. intuitively it seems to be the right move. I've had a few people asking me about that in PM over the years. and I tried myself when I just started being too curious for my own good. in fact, in the beginning I didn't have much of anything and I devised a way to find the impedance of a DAP by measuring the variation between 200hz and 2khz on my jh13 because those were the only known impedances I had ^_^. I did this with a headset microphone stuck to the nozzle
. #shamescience