If you're the least bit handy, this is what's behind the fabric of an awful lot of very expensive panels: https://www.amazon.com/Owens-Corning-703-Fiberglass-Boards/dp/B005V3L834/ref=asc_df_B005V3L834/?tag=...
Nice thing about this, besides being dirt cheap compared to what they charge for the same thing once they cover it with fabric and call it an acoustic panel, is its super easy to cut to any shape with a sheetrock blade. Cheap and easy enough to experiment. So instead of buying some overpriced panel in some stock shape way bigger than you need you can cut whatever size and cover with whatever fabric you want.
Just remember when it comes to fabric the ones closest to speaker grille material are the most effective at letting the panel absorb. Tight weave dense fabric starts to reflect when stretched over a panel.
Nice thing about this, besides being dirt cheap compared to what they charge for the same thing once they cover it with fabric and call it an acoustic panel, is its super easy to cut to any shape with a sheetrock blade. Cheap and easy enough to experiment. So instead of buying some overpriced panel in some stock shape way bigger than you need you can cut whatever size and cover with whatever fabric you want.
Just remember when it comes to fabric the ones closest to speaker grille material are the most effective at letting the panel absorb. Tight weave dense fabric starts to reflect when stretched over a panel.