Abstract: An air diffuser includes a mask plate spaced upstream from an orifice plate in a generally parallel relationship. The orifice plate includes openings in a first zone arranged in a non-linear pattern, inside a second zone arranged in a linear pattern. Both zones can be within a peripheral wall defining the spacing between the mask plate and the orifice plate. The mask plate has a large opening for air, with a footprint slightly larger than the first zone. The density and zone arrangement of the mask plate and the orifice plate results in a better umbrella pattern flow of air exiting the diffuser.