The Sensitivity of the Ear as a Function of Pitch

Abstract

Sensitivity-frequency curves as determined by continuously varying the pitch for different intensity levels.—The threshold sensitivity curve for audition may be determined by varying the intensity at many different pitches, or by varying the pitch at many intensities, noting the ranges of pitch which are audible for each intensity. The latter method enables irregularities in the curve to be more easily and surely determined. In these experiments, a thermophone actuated by current from a vacuum tube oscillator was used, the pitch being controlled by means of a continuously varying inductance, and the threshold sensitivity curve for the frequency range of 360 to 3000 per sec. was determined by the use of successive levels of intensity having an intensity ratio of 2:1. Curves were obtained for thirty normal ears. They show remarkable individual irregularities, not only being different for different individuals, but often for the two ears of the same person. In several cases the sensitivity changes by a factor of 200 to 1000 with a change of pitch of a semi-tone. An acceptable theory of the mechanism of audition must explain such abrupt changes. The average sensitivity increases from ${10}^{-7.2\mathrm{}}$ for 360 to an approximately constant value of ${10}^{-8.6\mathrm{}}$ ergs/${\mathrm{cm}}^2$/sec. for frequencies above 1300 per sec.