Abstract: A panel-like sound absorbing structure comprising an upper surface, a lower surface separated from said upper surface and a side surface connecting said upper surface to said lower surface. In the interior of the structure there are a plurality of quarter wave sound absorbing channels disposed in a planar array between said upper and lower surface, said channels having a first, sound-receiving, end into which sound waves are introduced and an end remote from the sound-receiving end, and means for introducing sound waves into said first end of said quarter wave sound absorbing channels. The distance between said upper surface and lower surface is not greater than about 1″. Alternatively, the interior of the structure can contain one or more Helmholtz resonator cavities.