Plexiglass is too damned expensive and the pre-made ones cost an arm and a leg. It's a pretty big set and it's on a rack, so it needs to be collapsable but effective. I considered just getting sections of plywood, hinging them together and covering them in egg crate. Would that work? If not, what would?
First question: do you wanna be able to see what's going on outside the booth? If so you'll need that Plexiglas, if not the plywood egg crate would do.
Couple of things you need to know: Do you want to cut out sound in the room you're playing/recording or you want it to be more quiet for the neighbours? If you wanna control in room sound it'll work, if you wanna mute it down it won't. The sound inside a room is pretty much reflective sound, so fairly easily controllable with just panels (or plywood and egg crate in our case).
But the sound transferring from one room to another is what's called structural noise and that my friend is a whole other beast to deal with! Because structural noise can't really be heard but is more "felt" than anything else - think of a booming Honda Civic at a red light. You don't really hear what's going on in the car, but you can definitely feel it! The only thing that will attenuate this is adding mass to the walls, and in the end comes MUCH more expensive.
In any cases a plywood/egg crate combo will cut down some of it but be carefull not to invest too much money in something that "won't quite" do the job you're looking to do.
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