Abstract
Ear canal acoustics was examined using a one-dimensional lossy transmission line with a distributed load impedance to model the ear. The acoustic input impedance of the ear was derived from sound pressure measurements in the ear canal of healthy human ears. A nonlinear least squares fit of the model to data generated estimates for ear canal radius, ear canal length, and quantified the resistance that would produce transmission losses. Derivation of ear canal radius has application to quantifying the impedance mismatch at the eardrum between the ear canal and the middle ear. The length of the ear canal was found, in general, to be longer than the length derived from the one-quarter wavelength standing wave frequency, consistent with the middle ear being mass-controlled at the standing wave frequency. Viscothermal losses in the ear canal, in some cases, may exceed that attributable to a smooth rigid wall. Resistance in the middle ear was found to contribute significantly to the total resistance. In effect, this analysis “reverse engineers” physical parameters of the ear from sound pressure measurements in the ear canal.
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Acknowledgments
Robert Withnell is indebted to the School of Mechanical Engineering at The University of Western Australia for generously hosting his sabbatical and for the award of a Gledden Senior Research Fellowship that provided the impetus for this work. Doug Keefe, Mead Killion, and one anonymous reviewer, provided valuable feedback and advice on earlier versions of this paper. Portions of this paper were presented at the Mechanics of Hearing 2011 conference in Williamstown, MA, USA and the American Auditory Society conference in Scottsdale, AZ, USA.
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Withnell, R.H., Gowdy, L.E. An Analysis of the Acoustic Input Impedance of the Ear. JARO 14, 611–622 (2013). https://doi.org/10.1007/s10162-013-0407-y
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DOI: https://doi.org/10.1007/s10162-013-0407-y