Dictionary.net

(Aureal 3-Dimensional?) A technology developed byAureal that delivers sound with a three-dimensional effectthrough two speakers. Many modern sound cards and PC gamesnow support this feature.A3D differs from the various forms of surround sound in thatit only requires two speakers, while surround sound typicallyrequires four or five. It is sometimes less convincing thansurround sound but is supposedly better in interactiveenvironments. For example, PC games in which sounds oftenmove from one speaker to another favour A3D, whilepre-recorded video favours surround sound. (http://a3d.com/).