Abstract
The effective volume of auditory canal has been measured with a small T form acoustic pipe. To each end of the horizontal part of the pipe are attached a small crystal earphone and a small crystal microphone, respectively; and the hole in the end of vertical part is connected closely with the auditory canal of an ear. The sound is produced by the earphone and the intensity of sound transmitted through the pipe is measured with the microphone. Next, the vertical part of the pipe is connected with the glass tube (7mm in diameter) containing the water in place of the auditory canal. By controling the height of water column we can reproduce the same out-put voltage in the microphone as that when connected with the ear. From the volume of the tube above the water column we can obtain the equivalent volume of the auditory canal. The frequency character of the effective volume has a minimum in the range between about 800 and 1200 cps. The minimum volume is about 0. 4 to 1. 0cc. In the frequency range lower than the minimum frequency the volume is almost constant and shows the personal difference (0. 9〜2. 3cc), and at the higher frequencies it is also almost constant and is about 1. 2cc. It is considered that this minimum is caused by the resonance of the middle ear mechanisms.
