Specification of the geometry of the human ear canal for the prediction of sound-pressure level distribution.

The geometry of 15 human ear canals has been studied. Silicone rubber molds were made of the ear canals of human cadavers, and a mechanical probe system was used to obtain approximately 1000 coordinate points over the surface of each mold. The data points were accurate to about 0.03 mm in each of the three space directions, allowing ample resolution of surface detail. The measurements have been summarized as individual ear canal area functions, the area of cross-sectional slices normal to a curved central axis following the bends of the canal. Large intersubject differences were found, but several overall trends were evident in the area functions. Accurate specification of the canal geometry has lead to improved predictions of the sound-pressure distribution along the human ear canal at frequencies greater than 8 kHz. Such predictions are relevant to the development of high-frequency audiometric methods, high-fidelity hearing aids, and to the interpretation of experiments in physiological and psychological acoustics.