Kruger B, Tonndorf J
J Acoust Soc Am. 1978 Feb;63(2):436-41. doi: 10.1121/1.381735.
In cat, a small tympanic membrane (TM) perforation produces a low-frequency loss--in terms of sound pressure changes (deltaSP) in front of the TM re a 10-micronV round window cochlear microphonic (RW CM)--that varies inversely with frequency at a rate of 12dB/octave with a surgically shortened external auditory meatus (EAM). Losses were determined at the outer opening (deltaSP00) and at the TM (deltaSPTM) of four artificial EAM's of various lengths, volumes, and leakiness. In the low-frequency region, a leaky EAM produced a flat loss. In the midfrequency region, the flatness of losses was attributable to (1) the length of the EAM and (2) the location at which the loss was determined. EAM volume was not related to the configuration of the loss. Losses, under all conditions, were always identical in shape and magnitude for the open and closed systems. Clinically, hearing losses due to TM perforations are essentially frequency independent, especially in the low frequencies. The relation between voltage changes (deltaV) across the transducer and losses with different EAM's suggests that the discrepency between audiometric results and CM losses--at least in the high and midfrequencies--may be due to the use of precalibrated SPL's in clinical audiometry.
在猫身上，小鼓膜（TM）穿孔会导致低频听力损失——就TM前方声压变化（deltaSP）与10微伏圆窗耳蜗微音器（RW CM）相比而言——在手术缩短外耳道（EAM）时，该损失随频率呈反比变化，变化率为每倍频程12分贝。在四个不同长度、容积和渗漏情况的人工EAM的外开口（deltaSP00）和TM（deltaSPTM）处测定了损失。在低频区域，渗漏的EAM会产生平坦的损失。在中频区域，损失的平坦度归因于（1）EAM的长度和（2）测定损失的位置。EAM容积与损失的形态无关。在所有条件下，开放系统和封闭系统的损失在形状和大小上始终相同。临床上，TM穿孔导致的听力损失基本上与频率无关，尤其是在低频。换能器两端电压变化（deltaV）与不同EAM的损失之间的关系表明，听力测定结果与CM损失之间的差异——至少在高频和中频——可能是由于临床听力测定中使用了预先校准的声压级。
