Boys Town National Research Hospital, 555 North 30th Street, Omaha, Nebraska 68131, USA.
J Acoust Soc Am. 2020 Jan;147(1):300. doi: 10.1121/10.0000588.
Causality-constrained procedures are described to measure acoustic pressure reflectance and reflection function (RF) in the ear canal or unknown waveguide, in which reflectance is the Fourier transform of the RF. Reflectance calibration is reformulated to generate causal outputs, with results described for a calibration based on a reflectance waveguide equation to calculate incident pressure and source reflectance in the frequency domain or source RF in the time domain. The viscothermal model RF of each tube is band-limited to the stimulus bandwidth. Results are described in which incident pressure is either known from long-tube measurements or calculated as a calibration output. Calibrations based on constrained nonlinear optimizations are simpler and more accurate when incident pressure is known. Outputs measured by causality-constrained procedures differ at higher frequencies from those using standard procedures with non-causal outputs. Evanescent-mode effects formulated in the time domain and incorporated into frequency-domain calibrations are negligible for long-tube calibrations. Causal reflectance and RFs are evaluated in an adult ear canal and time- and frequency-domain results are contrasted using forward and inverse Fourier transforms. These results contribute to the long-term goals of improving applications to calibrate sound stimuli in the ear canal at high frequencies and diagnose conductive hearing impairments.
因果约束程序用于测量耳道或未知波导中的声压反射率和反射函数（RF），其中反射率是 RF 的傅里叶变换。反射率校准被重新制定为生成因果输出，结果描述了基于反射波导方程的校准，以计算频域中的入射压力和源反射率或时域中的源 RF。每个管的粘滞热模型 RF 被限制在刺激带宽内。结果描述了在已知长管测量中的入射压力或作为校准输出计算的入射压力的情况。当已知入射压力时，基于约束非线性优化的校准更简单且更准确。当使用具有非因果输出的标准程序时，因果约束程序测量的输出在较高频率下会有所不同。在时域中制定并纳入频域校准中的渐逝模式效应对于长管校准来说可以忽略不计。在成人耳道中评估因果反射率和 RF，并使用正向和反向傅里叶变换对比时间和频域结果。这些结果有助于长期目标，即提高在高频下校准耳道中声音刺激的应用，并诊断传导性听力障碍。
