Oh great! Now I got it. Thanks! I won't cover whole ceiling though. I'll put an absorber over the listening position and will do like 8x5,6 feet cloud over recording position. Unfortunately my room has so low ceiling I can't do more than 2" absorber with 2" air gap. I even removed some coating (? is that a right term?) from ceiling to get few centimetres (sorry by switching from imperial to metric) of height. By the way speaking of air gap. Does the air gap have to be "connected to the air of the room? I mean here's and image of how I'm going to construct my clouds.