Thx Kyle...... I have 3kPas material but not enough. So I have an absorber that does not have a flat AC curve as advised, but they are flat around 50-120Hz where I need them. I can try an model a solution with flatter curves.... These absorbers are away from the live end so what they do above 150Hz will be overshadowed by the diffuse return of closer walls. If I was sitting in a mix chair with these 5 feet away, case would be different. I can partially cover them with something to return some over 150-200Hz. This problem is not mentioned in F.A.Everest book or Kleier/Tichy, I will check Tools book ++ later. I have an 4" absorber hanging 24" in front of a window, works wonderful. All the worlds 16" suspended ceilings will have this problem and rendered not working? Is there no proof of this in text somewhere???