The Haas and/or Precedence Effects in Sound Localization

When two or more sound sources radiate identical complex signals, the listener tends to hear only a single image located at the nearer source, providing the maximum delay is less than about 50 msec. This phenomenon (together with other closely associated aspects) is generally referred to as the “precedence effect” or Haas effect.” Less frequently, the terms “Law of the First Wave Front,” “auditory suppression effect,” and “threshold of extinction” have also been used in describing certain of these characteristics. Perhaps the earliest investigator to leave a clear record of his appreciation of the single image aspect of the phenomenon was Joseph Henry who, in 1849, used the term “limit of perceptibility” in describing what he had observed. The present paper will give some of the historical background of the effect primarily from the standpoint of its investigation and its application in electro-acoustical systems. In addition, some recent data on the influence of multiple equal-energy sources on the accuracy of localizing the apparent single source will be given.