Q: What’s the best way to hang acoustic foam on the wall, so that I can easily move it or take it down?
The easiest, least-destructive “temporary” solution is to use heavy pushpins or thumbtacks to hold the foam to the wall. I typically have used six or so tacks across the top of the foam, a few across the center, and four to six across the bottom. If you don’t use enough tacks, they’ll pull through the foam and it will fall down.
What I’ve done in several studios is to glue the foam to light plastic garden trellis, cut to be slightly smaller than the length and width of the foam. (You could also use posterboard.) You can then hang the trellis on the wall like a picture. For an even better solution, frame out the trellis material with 1×1″ wood, creating a rigid unit that can be hung on the wall or even hung from the ceiling on hooks/wire to create an acoustic “cloud” over the mix position. This has the advantage of spacing the foam away from the wall by an inch or more, improving the absorption of lower midrange and even higher bass frequencies.