Khanna S M, Stinson M R
J Acoust Soc Am. 1985 Feb;77(2):577-89. doi: 10.1121/1.391876.
The sound fields that arise in the auditory canals of cats have been examined both experimentally and theoretically. Of particular interest was the spatial variation of sound pressure near the eardrum, where reference probes are typically located. Using a computer controlled data acquisition system, sound pressure was measured between 100 Hz and 33 kHz for constant driver input at 14 different locations in the ear canal of a cat, and the standing wave patterns formed. The shape of the patterns could be predicted quite well above 12 kHz using a theory that requires specification of only the geometry of the ear canal. This theory, an extension of the one-dimensional horn equation, applies to three-dimensional, rigid-walled tubes that have both variable cross section and curvature along their lengths. Large variations of sound pressure along the ear canal and over the surface of the eardrum are found above about 10 kHz. As a consequence it is not possible to define the acoustical input to the ear from sound pressure level measured at any single location. Even in comparative experiments, in which only the constancy of the acoustical input is important, any uncertainty in reference probe location would lead to an uncertainty in sound pressure level when different sets of measurements are compared. This error, calculated for various probe locations and frequencies, is especially large when the probe is near a minimum of the sound field. Spatial variations in pressure can also introduce anomalous features into the measured frequency response of other auditory quantities when eardrum sound pressure is used as a reference. This is illustrated with measurements of the round window cochlear microphonic.
已经通过实验和理论研究了猫耳道中产生的声场。特别令人感兴趣的是鼓膜附近声压的空间变化，参考探头通常位于此处。使用计算机控制的数据采集系统，在猫耳道的14个不同位置，以恒定的驱动输入测量了100 Hz至33 kHz之间的声压，并形成了驻波模式。使用一种仅需要指定耳道几何形状的理论，可以很好地预测高于12 kHz时模式的形状。该理论是一维喇叭方程的扩展，适用于沿其长度具有可变横截面和曲率的三维刚性壁管。在高于约10 kHz时，发现沿耳道和鼓膜表面的声压有很大变化。因此，不可能根据在任何单个位置测量的声压级来定义进入耳朵的声学输入。即使在比较实验中，其中仅声学输入的恒定性很重要，当比较不同组测量时，参考探头位置的任何不确定性都会导致声压级的不确定性。针对各种探头位置和频率计算出的这种误差，当探头靠近声场最小值时特别大。当以鼓膜声压为参考时，压力的空间变化也会在其他听觉量的测量频率响应中引入异常特征。这通过圆窗耳蜗微音器的测量得到了说明。
