Most fabric is pretty neutral acoustically, and you have to go out of your way to find fabrics that are either specifically transparent or specifically absorbative. My guess (and this is just a guess) is that you could probably use just about any off-the-shelf fabric (From someplace like JoAnn's) and cover your QRD's without having any audible effect on their function. Maybe you'd be able to calculate or even measure an effect, but I'm betting that's a pretty thin "maybe". I'm also thinking that your suggestion to use a "breathable" fabric is right on the money. The more open a weave you use, the smaller the fabric's effect on passing waves.
If you want to be sure, PE sells grill cloth whose purpose is acoustic transparency. Seems unlikely that it would match your absorbtion panels though, unless you used the same stuff for the whole project. That's probably a lot more expensive though.
If you want to be sure, PE sells grill cloth whose purpose is acoustic transparency. Seems unlikely that it would match your absorbtion panels though, unless you used the same stuff for the whole project. That's probably a lot more expensive though.
