Sound Pressure Generated in an External-Ear Replica and Real Human Ears by a Nearby Point Source

A rubber replica has a pinna, concha, and auditory meatus with dimensions comparable with those of real human ears. At the eardrum position, there is provision for a totally reflecting termination (hard wall) or for various eardrum impedance networks. The replica is mounted in a rigid plane, and a point source at a distance of 8 cm provides sound with various angles of incidence over the frequency range 1–15 kHz. The sound pressure is measured with a probe-tube microphone at selected positions in the open canal and at the center of a plug closing the ear-canal entrance (“meatus-blocked” condition). The response with open canal and the response with blocked meatus have virtually identical angular dependence up to 12 kHz. From 2–7 kHz, there is substantial acoustic gain at the eardrum position associated with a fundamental canal resonance (M1) and a second mode largely controlled by a depth resonance of the concha (M2). Pressure distributions in the canal and concha are given for M1, M2, and three other modes. Limited data for six real ears with open and blocked canal are in good agreement with replica measurements up to 7 kHz. At 8 kHz, however, the on-axis response of real ears passes through a sharp minimum that is either removed to a higher frequency or is largely absent with the sound source above the axis.