Shape and sound analyses of the human ear-canal geometry

The curved centerline of the ear canal, and its spatial variations of area, transverse to this centerline influence sound transmission in the human ear canal at higher frequencies. The area function was directly assessed from images obtained using a hand-held device inserted into the canal and compared to sound area functions indirectly calculated from acoustical measurements. For shape data, areas were calculated by modeling each canal cross section as an ellipse. In a discrete Frenet frame procedure, the shape outputs were the spatial variations of ellipse area and eccentricity, with the curvature and torsion parameters representing the centerline. The resulting shape area functions were compared with sound area functions by finding the best alignment of the functions in each ear. The median shape and sound areas of the ear canal agreed within 0.3 mm2 at the probe tip and approximately 6 mm2 at 3.6 and 7.2 mm lateral to the probe tip. This supports the potential use of acoustical assessment of ear-canal area in future research.