Onset and Growth of Aural Harmonics in the Overloaded Ear

Abstract

The threshold of overload and growth in intensity of aural harmonics were determined by the exploring tone method for frequencies of 100, 350, 1000, 2000, and 5000 cps. The level of a test tone which first overloads the ear can be quite accurately determined and the range of beats between the second harmonic and the exploring tone, as the latter is changed in in-tensity, is considerably narrower at the overload threshold level than at higher levels. As the test tone is raised in intensity the loudness of the harmonic increases rapidly. Overloading occurs at approximately the same sound pressure level for all frequencies so that the range of linear response is about 8 db at 100 cps, 30 db at 350 cps, and 50 db at 1000, 2000, and 5000 cps. All harmonics are detected when they reach a certain consistent level above threshold for that frequency; the exact level depends upon the subject. Results are considered as additional evidence that distortion in the ear takes place within the sensory cells as part of the electromechanical process and is not due to any non-linearity of the mechanical response of the ear.