Here is the mdat:
Excellent! I just downloaded it and took a look at it: and overall, things are not as bad as they seem from the graph images posted earlier!
First, the 41 Hz peak:
... it really isn't totally terrible, and as Glenn already pointed out, it can be treated with EQ: A parametric filter applied at around 41 Hz with a cut of maybe 6 dB would probably do the trick. Adjust the bandwidth for the best result (but don't make it too wide! There's a phase shift at around 33 Hz, that you should stay away from). Another filter at around 280 Hz, -4dB and fairly broad would help even out that low-mid peak (there's no phase issues here, so you should be able to make it fairly wide: maybe half an octave or so.).
Next: There's a strange dip on all measurements at around 4.7 kHz:
That seems to be either your speakers themselves, or something in the signal chain. That is very unlikely to be an acosutic issue with the room, or the mic placement, since it is the same for all three measurements (speakers individually and also together). It also is not the calibration file: removing that does not change that region at all. It might be the measurement mic, but also not so likely. My guess is speakers, or something in the signal chain (EQ?).
One more: There's a rather large reflection arriving at your mix position from "somewhere", at around 4.4 ms after the direct sound:
That implies a specular reflection that is taking a path that is 152 cm (about 5') longer than the direct path. You can use the "string trick" to find out what surface is causing that, so you can fix it. That's a fairly serious reflection, since it is quite big (about -15dB) and quite early (4.4 milliseconds), so it deserves treating.
On that same graph you can see that the overall decay times are rather low for your size room: T20 is around 80 ms, and T30 is around 130 ms. I would shoot for something more like 160 ms for that size room, maybe even more if you can. In other words, there is too much surface area of insulation exposed directly to the room, so it needs some type of diffusive/reflective surfaces on top of it. That won't affect the low end absorption (which you need!), but it will improve the mids and highs. You just need to be careful that you don't cause any new specular reflections back to the mix position.
Those are the "big" issues that I see in your data: everything else looks quite reasonable, and your room should be pretty good, once you solve those.
Finally, reinforcing what Glenn said: Do not try to boost the frequency "dips" with EQ! That can create more problems than it solves, since dips are almost always phase related, and applying EQ where there is a phase shift, is a recipe for disaster. Only use cuts, keep the bandwidth adjusted to only deal with one issue, and don't over-do it with excessively large cuts. Just enough to "take the edge off" the peaks.
- Stuart -