Localization of sound in rooms VI: Duplex theory.

Six human listeners attempted to locate the sources of sine tones in three room environments with greatly different reverberation times. During the experiment, probe microphones recorded the signals in the listeners' ear canals in order to measure the interaural time differences (ITD) and the interaural level differences (ILD) that enable sound localization. Comparison of the interaural differences with listener localization responses showed the dominant weight of ITD at low frequencies and of ILD at high frequencies, consistent with Duplex theory. Equal ITD and ILD weights occurred at a crossover frequency between 400 and 600 Hz, apparently independent of room environment. Comparing results for near and far sources revealed dramatic effects of source distance on the correlations between interaural differences and source azimuths but little effect on the correlations between interaural differences and listener responses. Front-back reversals were rare for young listeners but frequent for older listeners. The experiment for intermediate reverberation time was repeated with headphones for the same six listeners using listener-specific signals from the rooms measurements. The frequency dependence of the weights for interaural cues was similar to that found in rooms.