Characterizing the eardrum admittance: Comparisons of tympanometry and reflectance

The residual ear canal (REC) between the probe and tympanic membrane (TM) is a significant source of non-pathological variability for acoustic measurements made in the ear canal. Tympanometry and reflectance, which seek to characterize the middle ear based on the TM admittance, must account for unknown REC dimensions. In tympanometry, the REC volume and 226 Hz TM admittance are estimated by varying the canal static pressure. Using a reflectance parametrization developed by the authors, typical assumptions for removing the REC effect are extended, and methods to estimate the REC volume and TM admittance are presented and compared to tympanometry. Results of this method are shown for reflectance measurements of human ears with varying static middle ear pressures (MEPs). The data show that the 226 Hz TM compliance is non-zero at tympanometric pressure extremes, and that acoustic parameters of the middle ear have highly variable, nonlinear dependence on the MEP level.