26 wabash slim 9 months ago I've never seen any absorption material in a chamber. They're all hard surfaced and covered in shellac. Movable curtains is something you might do in the tracking room. They used it to dampen the near field, or adjust other reflective parameters. Gave them a bit of control. Room was just going out of use when I'd started there in '79. Other than the rags, it was all plaster. No diffusion, just a bit of absorption, and a whole lot of reflective surfaces.