Low Frequency Thresholds of Hearing and of Feeling in the Ear and Ear Mechanisms

A redetermination of the hearing threshold in the frequency range 35 to 1000 cycles shows the minimum audible pressure in the ear canal to be inversely proportional to the cube of the frequency up to about 500 cycles. This is interpreted to mean that the form of vibration of the basilar membrane does not change appreciably and that the amplitude of its motion varies inversely as the square of the frequency in this range. It follows from this that the threshold stimulus for the nervous tissue is a constant acceleration. This observation also shows that the efficiency of the ear at high frequencies is principally due to the properties of nervous tissue and that the maximum mechanical efficiency occurs in the frequency range at 1000 to 2000 cycles. A redetermination of the threshold of feeling shows a nearly constant pressure at low frequencies which corresponds to a constant amplitude of motion at the ear drum and ossicles, suggesting that this sensation originates in the middle ear.