I picked up some cheap MDF perforated (slits) board, some had a little bit of absorber behind them. Would they be useful to put up against the walls as room treatment? I would add more absorber behind them, mostly they would be going where no 1st reflection treatments are, or behind the desk and speakers as an aesthetic item.

https://www.psiaudi…

Room dimensions - 14' 6" L x 12' 3" W x 7' 11" H
Construction material in room: old plaster walls, to my knowledge, no insulate material of any kind on the inside of the inside walls, OC R19 on the inside of the outside walls
2 windows,