Occlusion Effect of the External-Ear Canal and Its Effect upon Bone Conduction

Abstract

The study of this effect was recently included in a larger series of experiments in cats on bone conduction (BC). The effect was finally shown to have a dual cause, both contributing factors affecting the esseo—tympanic component of BC: radiation of sound by its osseous walls into the lumen of the external canal whence it is transmitted via eardrum and ossicular chain toward the cochlea. The two factors are: (1) The effect of a high-pass filter constituted by the open ear canal. (Elimination or reduction of this filter produces a low-frequency emphasis proportional with inverse frequency.) (2) An alteration of the resonant properties of the external canal. (This factor affects mainly the middle to high frequencies.) This concept combines aspects of earlier theories, notably those of Rinne (1855) and Huizing (1960) [resonance] and of von Békésy (1941) and Onchi (1954) [low-frequency emphasis]. The current results, in conjunction with earlier findings of the present long-range study, permit, for the first time, of a theory of BC compatible with observational facts, e.g., the clinical tests of Bing, Runge, Weber, and Gelle. Explanations for all of these differ slightly, but significantly, from each other. [This study supported by a Public Health Service, U. S. Department of Health, Education, and Welfare grant.]