Measuring Ear-Canal Reflectance and Estimating Ear-Canal Area Functions and Eardrum Reflectance

Abstract

Ear-canal reflectance contains information about ear-canal cross-sectional area functions and eardrum reflectance. These are important in audiology and the design of modern hearing aids and headphones. This paper investigates the inversion method for jointly estimating ear-canal cross-sectional area function and eardrum reflectance, given the acoustic reflectance measured at the entrance of the ear canal. It is found through physical experiments and simulations that the estimated cross-sectional area function is spatially band-limited to $2F_{c}/c$, where $\pmb{F}_{c}$ is the frequency bandwidth of the low-pass filtered reflectance used in the inversion, and $c$ is the speed of sound. If the actual spatial bandwidth of the area function under estimation is higher than this, then Gibbs ripples appear in the estimated area function. A method is presented for the accurate measurements of ear-canal reflectance, and results are presented for two subjects along with the estimated ear-canal area functions and eardrum reflectance.