Originally Posted by wiz561
Thanks for the idea, but I'm not exactly sure that this would give an accurate view of the IEM itself. I suppose that by doing something like what you're suggesting, it would equalize the equipment. To make sure I understand you, you're saying to do that, then look at the frequency curve for the IEM, and do a diff to set the equalizer? Are there any references or howto's out there that explain how to do this better?
Last time I hooked a multimeter up to some equipment, I think I was about 9 or 10 years old. I forget what it was, but I want to say something started smoking! Ever since then, I've been a little leery about doing it again. On the other hand, it was 20 years ago and I didn't know what an ohm was, or the difference between ac and dc!
I'm not sure if I follow what you're asking. Equalizing? There are some compromises and inaccuracies here, but there may be more in trying to actually do the acoustic measurement. Anyway, let's first assume we have an IEM with a flat frequency response, known to have sensitivity of 120 dB SPL / 1V input. This figure should be given by the manufacturer; a review site like InnerFidelity may have measured it as well. If it's given in dB SPL / 1 mW input, you can do some easy math to convert if you know the impedance.
Play music, set the volume how you would listen. Measure the voltage applied to the IEMs while this is going on (a splitter cable may be useful, just so you have something you can touch the measurement probes to; you want to measure between L or R channel and ground). Let's say it was 0.02V (rms). Then we know that the output SPL should be 120 - 20*log10(1 / 0.02) = 86 dB. Done.
In practice, manufacturer's spec may be slightly off. A cheap multimeter is not going to give an accurate true rms voltage reading. I doubt you have an oscilloscope handy. If you want, you could instead just play say a 50 Hz tone at roughly your listening volume, try again for a 500 Hz tone, etc., because they can actually read pure sine waves with no problem, unless they're out of calibration or can't handle that level or frequency. If the IEM has a much stronger response in some frequencies than others, you may have to consider that when picking out test tones, if you want to use pure sine waves.
Edited by mikeaj - 11/15/12 at 7:22am