Speaker grill material, any real difference?

There is no cloth that is acoustically transparent. Use your brain. ANYTHING that is placed in front of a transducer, WILL(in one way/degree or another)have an effect on the sound radiated. Some speaker systems are tuned for their grille cloths, but that is rare. That's why most systems sound better, with the grilles removed.

Granted anything will affect the sound, I like the way they sound with the grills on. Actually the manual states to leave them on as well. I think since these speakers have both planer type and cone type drivers the cover helpes blend the sound properly... Maybe?
"Single strand double knit polyester?" Sounds like one of my old disco shirts. I'll check it out, as well as the standard issue stuff.
-JD

Speaker designers final voice their speakers with the grills on....therefore, the fabric will make a difference. Take a sample of original grill material to your fabric store and ask for a duplicate material with similar weave.

Some "grill cloth" is more accurately described as "acoustically translucent" not "acoustically transparent".

Using whatever the speakers were designed for would be prudent.

Not to miller the thread, but what type of adhesive do you recommend to attach the cloth to grill frame? Im thinking of re-doing mine (manuf. says $400. for new ) but unsure of best adhesive. The frames are metal.