Hey y'all, I'm currently in the process of adding DIY acoustic treatment to my small (10' x 10' x 8' tall / 3m x 3m x 2.4m tall) bedroom to get a flatter room frequency response and decrease reverberation time, both of which will help contribute to more accurate mixes. After doing a bunch of research, as I understand it the first steps for small rooms are to:
1) treat first reflection points with acoustically absorptive material (typically mineral wool or fiberglass board)
2) add bass trapping in the corners (using the same materials, but double the thickness).
Treating first reflection points is helpful because you can create a reflection free zone at your mix position, aka where you are sitting while tracking / mixing. With proper placement of acoustic panels, you can absorb most mid- to high-frequency reflections off walls, floor and ceiling that would otherwise be heading back to your ears. These reflections, if not absorbed, would combine with the direct sound from your monitors and cause muddled sound / comb filtering due to destructive interference / phase cancellation. For a bit more info on this topic, check out this article: http://realtraps.com/rfz.htm
Bass trapping in the corners is particularly effective because bass builds up more in the 90 degree angle between any two walls (including the floor / ceiling) than it does in the middle of the wall. Installing thick (4-6" / 10-15cm) absorptive panels with an equally sized air gap behind them, in as many the corners of the room as possible, will help to absorb some of the bass frequencies bouncing around.
Also, there's some evidence that monitoring with two or more subwoofers greatly helps to flatten out the low-frequency response: http://mehlau.net/audio/multisub_geddes/
For plenty of further reading, here is a list of web and print resources: http://www.gearslutz.com/board/studio-building-acoustics/610173-acoustics-treatment-reference-guide-look-here.html
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