Apparent Source Width (ASW)

Discovered and developed by A. H. Marshall, ASW is a subjective parameter of spaciousness in concert halls, and is related to the level, at the listener′s ears, of lateral reflections in the first 50 to 80 milliseconds after the arrival of the direct sound.

Increasing the ratio of this reflected energy to the direct sound increases the sense of spaciousness. Narrow, rectangular, "shoebox-shaped" halls like the famous Symphony Hall in Boston tend to foster strong, early-arriving reflections from the side walls, subjectively broadening the sound source and imparting body and fullness to the music.

See also: Clarity, Room Acoustics.