I've read a good bit about designing a home studio, an application in which controlling reflections and standing waves is really critical. The articles I've seen on DIY projects to correct these issues have generally made it sound as though building a simple screen to reduce unwanted reflections in the mid-treble range is pretty easy and inexpensive.
OTOH, coming up with a trap to tame serious standing waves in the bass frequencies is another ballgame. A lot of it has to do with room dimensions. It also has to do with the density of the trap material. Simple pink insulation won't cut it, I believe.
However, I've never made a serious attempt at it myself, so this is all theoretical.
