Rosowski J J, Carney L H, Peake W T
Research Laboratory of Electronics, Massachusetts Institute of Technology Cambridge 02139.
J Acoust Soc Am. 1988 Nov;84(5):1695-708. doi: 10.1121/1.397185.
The configuration of external ears varies dramatically among mammalian species. In order to relate these structural differences to acoustic performance, it is useful to determine the "output" (radiation) impedance of the external ear. Measurements were made of the radiation impedance ZE of the cat external ear looking out from the location of the tympanic membrane. Freshly excised external ears were coupled to a calibrated sound source at the tympanic ring, and the resulting sound pressure at the source was measured. The ZE calculated from these measurements is masslike at frequencies below 2 kHz and approximately resistive above 4 kHz. The contributions of anatomically distinct sections of the external ear to ZE were assessed by measuring the impedance before and after surgical removal of the pinna flange and of the concha. Mean measurements of the lengths and cross-sectional areas of components of the external ear are used in a simple model that consists of a uniform tube and an exponential horn; the radiation impedance of the model shows many of the features of the measured ZE's. Measurements of the input impedance of the middle ear are combined with ZE to infer the diffuse-field absorption cross section ADF, which is a measure of the ear's performance as a coupler of acoustic power. It is suggested that ADF is useful for across-species comparisons of the performance of external and middle ears.
哺乳动物物种的外耳形态差异极大。为了将这些结构差异与声学性能联系起来，确定外耳的“输出”（辐射）阻抗是很有用的。从鼓膜位置向外测量了猫外耳的辐射阻抗ZE。将刚切除的外耳在鼓膜环处与校准声源耦合，并测量声源处产生的声压。从这些测量结果计算出的ZE在2kHz以下的频率呈质量状，在4kHz以上近似电阻性。通过测量耳廓边缘和耳甲手术切除前后的阻抗，评估了外耳解剖学上不同部分对ZE的贡献。外耳各组成部分的长度和横截面积的平均测量值被用于一个由均匀管和指数喇叭组成的简单模型中；该模型的辐射阻抗显示出许多实测ZE的特征。将中耳的输入阻抗测量值与ZE相结合，以推断扩散场吸收截面ADF，它是衡量耳朵作为声功率耦合器性能的一个指标。有人认为，ADF对于跨物种比较外耳和中耳的性能很有用。
