Revision of Estimates of Acoustic Energy Reflectance at the Human Eardrum

An improved analysis procedure has been applied to standing wave patterns measured previously [B. W. Lawton and M. R. Stinson, J. Acoust. Soc. Am. 79, 1003-1009 (1986)] in human ear canals. Revised acoustic energy reflection coefficients, at the eardrum, are obtained for 20 ears for frequencies between 3 and 13 kHz. The new analysis addresses anomalous features of the standing wave patterns, apparent at frequencies above 8 kHz, due primarily to the curvature of the ear canal. Much better agreement is now found, at these higher frequencies, between the theoretical form assumed for the standing wave patterns and the experimental data. The revised values of eardrum reflectance are somewhat smaller, especially for frequencies above 11 kHz. The reflectance rises from about 0.25 at 4 kHz up to 0.7 at 8 kHz, falls to a minimum of 0.5 at 11 kHz, then rises to 0.6 at 13 kHz. Considerable intersubject variability in the results is noted.