I needed to control hi-freq noise from the ceiling corners. I affixed 1 ft. square cardboard type egg trays with pushpins - two trays per front corner on the walls and one in each rear corner (rear wall). I only had six trays and I have a drop ceiling with a somewhat textured surface, so I felt I could forego placing them on the ceiling. The effect was well beyond my expectations. Photo is posted in DIY Projects gallery.