Attenuation of Tones Through a Spiral Canal -In Relation to the Origin of C5 dip-Hidetaka TAKEDA* We studied the acoustic characteristics of a spiral cavity in relation to the attenuation properties of the ear plugs with a spiral cavity (Takeda's ear plugs, UNTONE). A test was carried out with microphones placed in a model resembling an enlarged cochlea. Through the spiral air canal, pure tones (0.5, 1, 2, 3, 4, and 6 KHz) and white noise at 90 dB SPL were delivered. The output of the

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... s were studied using an oscilloscope. Microphone 2 (MIC-2) was placed where the sound from the source was at a minimum incident angle in the 1 st turn. MIC-1 was placed closer to the sound source than MIC-2 by 3cm. and MIC-3 was placed 25 cm further than MIC-2, in the second turn. Simultaneous mesurements were obtained. At 3 and 4 KHz, MIC-2 monitored the largest sound pressure, whereas this was not observed at 2 KHz or below or with white noise. MIC-1 monitored the largest sound pressure with a 6 KHz tone, presumably due to the fact that the shorter sound wave were more attenuated further down in the spiral canal. Depending on the structure of the air canal, resonance may influence our measurements.