HiPer flat panel diffuser combines absorption and diffusion into one sound panel. This device is similar in appearance to standard fabric-covered acoustical wall panels, such as Sonora®, and can be intermixed with them. Acoustical performance differs significantly from outward panel appearance. The patented internal structure uses two layers of absorption, separated by a barrier septum, to form a low-profile, composite absorber / diffuser product. Their constructive and destructive interference with incident sound, produced by the varied hole-pattern combinations, creates significant sound scattering in the critical mid-frequencies.