Whitehead M L, Stagner B B, Lonsbury-Martin B L, Martin G K
University of Miami Ear Institute, Florida 33101, USA.
J Acoust Soc Am. 1995 Dec;98(6):3200-14. doi: 10.1121/1.413810.
At frequencies above 3 kHz, standing waves in the ear canal complicate calibration of stimulus sound-pressure levels (SPLs) for measurements of distortion-product otoacoustic emissions (DPOAEs). In the literature, two stimulus-presentation strategies have been used for DPOAE measurements. In the "in-the-ear adjustment" strategy, the voltage command to the speakers is adjusted to maintain a constant stimulus SPL across frequency at the DPOAE-measurement microphone. In the "iso-voltage" strategy, the voltage presented to the speakers is held constant across frequency, on the basis of the assumption that the frequency response of the speakers is approximately flat at the eardrum in the average human ear canal. Because of standing-wave effects, there are large, systematic but idiosyncratic differences of stimulus SPL between the two strategies. DPOAE-versus-frequency functions ("DPOAE audiograms") obtained using both stimulus-presentation strategies in the same ears are presented. The differences of stimulus SPL between the two strategies, and the associated differences of DPOAE amplitude, are described and quantified. Around frequencies of standing-wave minima at the DPOAE probe, the in-the-ear adjustment strategy resulted in smaller DPOAEs at high L1 = L2, but much larger DPOAEs at low L1 = L2, than did the iso-voltage strategy. For any L1, the DPOAE-amplitude differences between the two strategies varied systematically with L1-L2. At the stimulus levels used to construct previously published population norms for clinical applications (i.e., L1 > or = 65 dB SPL), there are only small differences of mean DPOAE amplitudes, and of the standard deviations of these means, between the two strategies.
在频率高于3 kHz时，耳道中的驻波会使用于测量畸变产物耳声发射（DPOAE）的刺激声压级（SPL）校准变得复杂。在文献中，两种刺激呈现策略已被用于DPOAE测量。在“耳内调整”策略中，对扬声器的电压指令会被调整，以在DPOAE测量麦克风处保持跨频率恒定的刺激SPL。在“等电压”策略中，基于扬声器的频率响应在普通人耳道中的鼓膜处大致平坦这一假设，施加给扬声器的电压在整个频率范围内保持恒定。由于驻波效应，两种策略之间刺激SPL存在很大的、系统性但因人而异的差异。展示了在同一耳朵中使用两种刺激呈现策略获得的DPOAE与频率函数（“DPOAE听力图”）。描述并量化了两种策略之间刺激SPL的差异以及相关的DPOAE幅度差异。在DPOAE探头处驻波最小值的频率附近，与等电压策略相比，耳内调整策略在高L1 = L2时导致较小的DPOAE，但在低L1 = L2时导致大得多的DPOAE。对于任何L1，两种策略之间的DPOAE幅度差异随L1 - L2系统地变化。在用于构建先前发表的临床应用总体规范的刺激水平下（即L1≥65 dB SPL），两种策略之间平均DPOAE幅度以及这些平均值的标准差只有很小的差异。
