Acoustic Technology, Department of Electrical Engineering, Technical University of Denmark, Ørsteds Plads, Building 352, Kongens Lyngby, DK-2800, Denmark.
Caruso Department of Otolaryngology, University of Southern California, 1640 Marengo Street, Los Angeles, California 90033, USA.
J Acoust Soc Am. 2019 Aug;146(2):1464. doi: 10.1121/1.5124000.
Ear-canal reflectance is useful for quantifying the conductive status of the middle ear because it can be measured non-invasively at a distance from the tympanic membrane. 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.
耳道反射率可用于量化中耳的传导状态，因为它可以在距鼓膜一定距离处进行非侵入式测量。耳道反射率的推导需要将总声压分解为正向和反向传播分量。使用涉及耳道输入和特征阻抗的公式可以方便地实现这种分解。特征阻抗定义为传播波的声压与体积流量之比，对于均匀波导，平面波特征阻抗是实值常数。然而，在非均匀波导中，特征阻抗是复数量，取决于传播方向，并且更准确地描述了非均匀耳道中的传播波。本文回顾了平面波和球面波特征阻抗的相关特性。此外，还研究和比较了平面波和球面波反射率在表示中耳引起的反射、校准刺激水平以及模拟非均匀耳道中发射压力方面的应用。
