IEM Measurement Tools: Checking Out The Audix TM2 & SLS-Audio MiEMi

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That said, I’m really interested in the broad strokes here: does L match R? Do your IEMs measure the same tonight as they did last week? Much as with measuring a PA system, this is about the forest, not the trees.
As an interesting aside, it seems that a lot of IEMs have a high-frequency problem.

Figure 3 depicts my Mackie MP-240 in blue and a Shure SE-315 IEM in pink, normalized to the mid-band (500 Hz). The high-frequency of the SE-315 takes a bump up above 1 kHz and then falls off a cliff completely above 4 kHz, which seems to be a common trend. As more data becomes available, it may very well be revealed that this is a limitation of non-laboratory grade measurement couplers.

Figure 3: Mackie MP-240 (blue) and Shure SE-315 (pink), normalized to 500 Hz.

The SLS website has measurements of some other common IEM units and a lot of them exhibit the same trait. (Heads up – the SLS screenshots are magnitude on top, phase on the bottom, the opposite of what appears here. Many of them also use heavy smoothing and a greatly compressed vertical scale of +/- 35 dB or even more in some cases, which can make the responses seem flatter than they really are – just some things to be aware of when browsing the data on your own.)

My subjective perception of the SE-315 is that it has a little too much in the high-mid band, and it’s interesting to see that borne out in the data.

SPL Calculation

Another interesting (and dare I say very important) aspect of this is the ability to calibrate the TM2 for SPL and have an idea of what sort of sound exposure our artists are enduring – provided, of course, we control for variables such as the pack level knob, etc. I’ve found that artists I work with tend to set their pack levels once and then not touch them again, so I could in theory collect the packs after the show while still on and measure them at that point to get an accurate idea.

This is cool stuff – for purposes of sound exposure, we’re interested in average A-weighted levels (LAeq) or looking at the NIOSH dose directly as a percentage (%), as shown in Figure 4. One particular concern for me are artists who take out one side of their IEMs, which means turning up the pack much more to get the same perceived loudness. That extra 6 to 9 dB means four to eight times the sound exposure, not to mention what’s coming in the other ear. So, the ability to quantify the risk in these types of situations is a pretty cool and very welcome thing.

Figure 4: An example IEM SPL meter bridge in Smaart SPL, with NIOSH exposure dose on the right-most meter.

Currently, the MiEMi coupler isn’t able to be accurately calibrated for SPL, although I am told that a calibrator adaptor is in development.

Conclusions

I think these are both great tools and welcome additions to the monitor engineer’s toolkit. For consistency and spot checks, they’ll both do the job well once you get the hang of consistent and well-sealed insertions.

Remember that the TM2 is a self-contained unit whereas with the MiEMi you’ll need an EMX-7150 microphone as well. The mic is pretty popular in the measurement world, so you might already have one, and they’re also a solid investment – SLS sells the coupler and the mic as a bundle. The additional accuracy gained by the TM2 correction file is probably not super important in most circumstances, but the accurate SPL calibration is a big selling point in my opinion.

That’s my two cents, hopefully it’s helpful to anyone considering investing in one of these tools.