Ravicz Michael E, Olson Elizabeth S, Rosowski John J
Eaton-Peabody Laboratory, Massachusetts Eye & Ear Infirmary, 243 Charles Street, Boston, Massachusetts 02114, USA.
J Acoust Soc Am. 2007 Oct;122(4):2154-73. doi: 10.1121/1.2769625.
Sound pressure was mapped in the bony ear canal of gerbils during closed-field sound stimulation at frequencies from 0.1 to 80 kHz. A 1.27-mm-diam probe-tube microphone or a 0.17-mm-diam fiber-optic miniature microphone was positioned along approximately longitudinal trajectories within the 2.3-mm-diam ear canal. Substantial spatial variations in sound pressure, sharp minima in magnitude, and half-cycle phase changes occurred at frequencies >30 kHz. The sound frequencies of these transitions increased with decreasing distance from the tympanic membrane (TM). Sound pressure measured orthogonally across the surface of the TM showed only small variations at frequencies below 60 kHz. Hence, the ear canal sound field can be described fairly well as a one-dimensional standing wave pattern. Ear-canal power reflectance estimated from longitudinal spatial variations was roughly constant at 0.2-0.5 at frequencies between 30 and 45 kHz. In contrast, reflectance increased at higher frequencies to at least 0.8 above 60 kHz. Sound pressure was also mapped in a microphone-terminated uniform tube-an "artificial ear." Comparison with ear canal sound fields suggests that an artificial ear or "artificial cavity calibration" technique may underestimate the in situ sound pressure by 5-15 dB between 40 and 60 kHz.
在0.1至80kHz频率的封闭声场刺激过程中，对沙鼠的骨性耳道内的声压进行了测绘。一个直径1.27毫米的探管麦克风或一个直径0.17毫米的光纤微型麦克风沿着直径2.3毫米的耳道内大致纵向轨迹放置。在频率大于30kHz时，声压出现了显著的空间变化、幅度上的尖锐最小值以及半周期相位变化。这些转变的声频随着距鼓膜（TM）距离的减小而增加。在TM表面正交测量的声压在60kHz以下频率仅显示出小的变化。因此，耳道声场可以相当好地描述为一维驻波模式。根据纵向空间变化估计的耳道功率反射率在30至45kHz频率下大致恒定在0.2 - 0.5。相比之下，在更高频率下，反射率增加，在60kHz以上至少达到0.8。还在一个以麦克风为终端的均匀管（“人工耳”）中测绘了声压。与耳道声场的比较表明，人工耳或“人工腔校准”技术在40至60kHz之间可能会将原位声压低估5 - 15dB。
