An optimal spherical-head model is derived from the high-frequency interaural time difference (ITD) of a population of 25 subjects. Analysis demonstrates that the optimal sphere results in a very small lateral angle errors, except near5 the interaural poles. The spherical-head model is then estimated using the anthropometry of the subjects, based on simple and robust empirical predictive equations. Such a customization greatly decreases objective angular errors that occur when a generic model is used.