The Binaural Localization of Pure Tones

Abstract

Measurements of phase difference and amplitude ratio of the sound entering the ears of a man-shaped wax dummy were taken with the source at varying azimuths around the head; at 256, 1024 and 1944 cycles per second; and at distances of 20, 50, 100 and 400 cm. from the head. The measurements at the two frequencies agree with the values published by Hartley and Fry computed on the assumption that the head is a rigid sphere in free space, except that the observed values of amplitude ratio are about 13 per cent. less than the computed values on account of the interference of the neck. The observed values at 1944 cycles are quite different from the computed values. As a converse experiment, pure tones of frequency 256 cycles were presented binaurally to eight different observers, the phase difference and amplitude ratio of the acoustical pressures at the two ears being known and adjustable. The observers were asked to state the direction and distance of the apparent source of sound. Only three of the eight observers were influenced in their judgment of direction by the phase difference and even they were rather inaccurate. All were influenced more or less in judging direction by the amplitude ratio. None was able to tell the distance of the source by the amplitude ratio.