Before you spring big bucks for whatever size, I suggest you cobble together a cheap screen using whatever material you find at your local Hancock/Jo-Ann/Hobby Lobby store. Each run sales of material that could pass for screen fabric. If your to-be screen wall will allow, place your speakers and buy fabric that tends toward acoustic transparency. You can get white polyester fabric for $4+ per yard. That will get you a decent sized screen that you can use to test 1.78 vs. 2.35, speaker placement, screen width, etc. You don't even need a frame; just tack it up (tightly) to your target screen wall. Of course, you can get carried away, as I did, and build a temp DIY frame, wrap it with velvet (Hobby Lobby, Jo-Ann, Hancock), tack your screen fabric to the back of it, hang it on the wall and experiment. Also, several of the screen manufs. will sell small samples of screen fabrics. This is highly recommended, to check for its appearance in your space.