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Deriving the ear-canal reflectance requires decomposing the total acoustic pressure into its forward- and reverse-propagating components. This decomposition is conveniently achieved using formulas that involve the input and characteristic impedances of the ear canal. The characteristic impedance is defined as the ratio of sound pressure to volume flow of a propagating wave and, for uniform waveguides, the plane-wave characteristic impedance is a real-valued constant. However, in non-uniform waveguides, the characteristic impedances are complex-valued quantities, depend on the direction of propagation, and more accurately characterize a propagating wave in a non-uniform ear canal. In this paper, relevant properties of the plane-wave and spherical-wave characteristic impedances are reviewed. In addition, the utility of the plane-wave and spherical-wave reflectances in representing the reflection occurring due to the middle ear, calibrating stimulus levels, and characterizing the emitted pressure in simulated non-uniform ear canals is investigated and compared.<\/jats:p>","DOI":"10.1121\/1.5124000","type":"journal-article","created":{"date-parts":[[2019,8,28]],"date-time":"2019-08-28T15:33:23Z","timestamp":1567006403000},"page":"1464-1474","update-policy":"https:\/\/doi.org\/10.1063\/aip-crossmark-policy-page","source":"Crossref","is-referenced-by-count":7,"title":["On the calculation of reflectance in non-uniform ear canals"],"prefix":"10.1121","volume":"146","author":[{"given":"Kren Rahbek","family":"N\u00f8rgaard","sequence":"first","affiliation":[{"name":"Acoustic Technology, Department of Electrical Engineering, Technical University of Denmark , \u00d8rsteds Plads, Building 352, Kongens Lyngby, DK-2800, Denmark"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Karolina K.","family":"Charaziak","sequence":"additional","affiliation":[{"name":"Caruso Department of Otolaryngology, University of Southern California , 1640 Marengo Street, Los Angeles, California 90033, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Christopher A.","family":"Shera","sequence":"additional","affiliation":[{"name":"Caruso Department of Otolaryngology, University of Southern California , 1640 Marengo Street, Los Angeles, California 90033, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"231","published-online":{"date-parts":[[2019,8,28]]},"reference":[{"key":"2023071923184412200_c1","first-page":"278","article-title":"Acoustic propagation in flaring, axisymmetric horns: I. 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