The Pressure Distribution in the Auditory Canal in a Progressive Sound Field

Abstract

The variation of the sound pressure along the auditory canal was determined experimentally on a number of subjects, male and female, placed in a progressive sound field. This was accomplished by insertion of a small flexible probe microphone at various positions along the length of the auditory canal. The subjects were placed in the sound field of a loudspeaker in a room free from acoustic wall reflections. The measurements were carried out over the significant range of audio-frequencies at various orientations in azimuth of the subjects with respect to the sound source. The free-field sound pressure was also determined at the subjects' location. The sound pressure at the eardrum is greater than the free-field pressure. The average ratio of these two quantities is a function of frequency and reaches values of about 20 db in the vicinity of 3000 c.p.s. The human ear is thus an effective acoustic “amplifier.” This amplification is a combination effect of diffraction around the head and pinna and resonance in the auditory canal. The measurements of the sound pressure at some of the other positions along the auditory canal serve to separate these two phenomena to a certain extent and to furnish additional information about the pressure distribution in the auditory canal.