耳珠のはたらき

抄録

The human tragus is bigger than that of other animals, and it overhangs the front of the entrance to the auditory canal. Thus, it is probable that the tragus is related to acoustic function of the external ear. Since no acoustic studies have been reported to date, the author examined the acoustic function of the tragus.
The source of sond was a Function Generator (TECTRONICS FG 504), and the response curves were measured in a linear scale (the frequency range was from 0.1k to 10kHz). Sound pressure was measured by a very small condenser microphone (RION EU-22), which could be placed in the auditory canal. The data were averaged and analyzed by an Analyzing Recorder (YEW MODEL 3655).
Included in this study were one subject with a tragus defects, ten subjects with normal ears, an external ear replica (KOKEN LM 7#1202), an auditory canal model (Plastic) and a tragus model (clay model).
The results were as follows:
1. The tragus increased the acoustic length of the auditory canal (by about 3mm), lowering the frequency of the canal resonance (about 200Hz).
2. The tragus helped the acoustic function of the pinna, and it raised the acoustic response of 4k to 8kHz up to about 5 to 7dB.
3. The tragus forms part of the horn shape of the external ear, and it causes the acoustic response of the horn under 8kHz to be a flat response.
Therefore the acoustic function of the tragus in the human is of obvious importance to the function of the external ear.