Robust transformation of middle ear impedance parameters from an intra‐aural measuring plane to the eardrum

Abstract

In order to eliminate the risk inherent in the insertion of a measuring probe into the ear canal of a subject, a middle ear impedance transducer should be placed a safe distance away from the eardrum. A technique presented in this paper uses a function which represents the area function of the ear canal and transforms impedance parameters from the measurement plane to a plane at the eardrum. The effects of the geometry of the canal on impedance measurements, and the validity of the approximations over a wide frequency range are studied by means of a computer model. The area functions used to transform the impedance parameters are parabolic horns which are found to provide better results than the commonly used cylindrical approximation. The sensitivity of these approximations to errors in the estimation of the parameters defining the horn is also studied. The parabolic horns give a simple and very reliable correction to the interpretation of middle ear impedance data. [Work supported by the Natural Sciences and Engineering Research Council of Canada, CRD‐8422.]