The success of open-plan offices and schools is dependent on the acoustical environment in providing the privacy accomplished by and experienced in conventional partitioned rooms. The acoustical environment is provided by the extensive use of efficient sound-absorbant materials and constructions on all surfaces of an appropriate area, location of acoustical screens in relation to noise sources, conversational and business machine activity, and suitable mechanically or electronically produced background noise. The principle behind the use of sound-absorbent material on all room surfaces is to eliminate virtually all the propagation of sound energy by surface reflection. The over-all sound absorption within the area is dictated by the type of material and its surface extent and the application. In regard to acoustical efficiency, the ceiling is considered to be most critical, not only for sound absorption but also for sound diffusion, with acoustical screens, walls, and floor following in that order. Thus, the propagation distance for speech and/or business machine frequencies, the relative degree of privacy or speech intelligibility, can be determined quite satisfactorily by knowing the sound-absorbing efficiency of the area and introducing the appropriate mechanically and/or electronically produced background masking noise.