Whatever fabric you choose should be as acoustically transparent as possible for the panel behind to do its job without interference from the fabric. There is a lot of variability in how acoustically transparent different fabrics are, but generally speaking the thicker the fabric and the tighter the weave, the less acoustically transparent and more absorptive it will be and vice versa. Each manufacturer should have ratings for the acoustic transparency of their different fabric types. The test methods are not consistent from company to company from what I have seen, but should give you a general idea of the differences. Good luck!