Siegel J H, Hirohata E T
Department of Communication Sciences and Disorders, Northwestern University Evanston, Illinois 60208.
Hear Res. 1994 Nov;80(2):146-52. doi: 10.1016/0378-5955(94)90106-6.
Distortion product otoacoustic emissions offer the potential for assessing inner ear function at high frequencies. However, commonly employed methods for calibrating the acoustic system used in these studies can lead to errors of +/- 20 dB or more in the estimate of eardrum sound pressure levels above 2-3 kHz [Siegel, J. Acoust. Soc. Am. 95, 2589-2597 (1994)]. We assessed the magnitude of these errors by measuring the distortion product emission 2f1-f2 (f1 < f2) in human subjects using either of two microphone locations to calibrate the stimulus. Either the emission probe microphone itself or a probe tube positioned near the eardrum were used in calibrations. The emissions collected with f1 in the vicinity of 5-7 kHz showed a pronounced peak in level relative to other stimulus frequencies when the emission probe was used for calibration. The peak at 5-7 kHz disappeared when the probe tube near the eardrum was used for calibration. The discrepancy in emission levels between the two calibration procedures was as large as 20 dB. The difference is attributed to the presence of standing waves in the ear canal. The systematic errors in estimating eardrum sound pressure level using the emission probe microphone undoubtedly contribute to the variability of emission measurements for high-frequency stimuli.
畸变产物耳声发射为评估高频下的内耳功能提供了可能。然而，在这些研究中，用于校准声学系统的常用方法可能会导致在估计2 - 3kHz以上的鼓膜声压级时产生±20dB或更大的误差[Siegel, J. Acoust. Soc. Am. 95, 2589 - 2597 (1994)]。我们通过在人类受试者中测量畸变产物发射2f1 - f2（f1 < f2）来评估这些误差的大小，使用两个麦克风位置中的任何一个来校准刺激。校准中要么使用发射探头麦克风本身，要么使用位于鼓膜附近的探管。当使用发射探头进行校准时，在5 - 7kHz附近收集的f1发射相对于其他刺激频率在水平上显示出明显的峰值。当使用鼓膜附近的探管进行校准时，5 - 7kHz处的峰值消失。两种校准程序之间的发射水平差异高达20dB。这种差异归因于耳道中驻波的存在。使用发射探头麦克风估计鼓膜声压级时的系统误差无疑导致了高频刺激发射测量的变异性。
