Theoretical and applied external ear acoustics.

The external ear (pinna and earcanal) plays a major role in transforming acoustic signals from free field to the tympanic membrane in humans. It acts as a filter to reduce low frequencies, a resonator to enhance mid frequencies (2.0 to 7.0 kHz), and a direction-dependent filter at high frequencies to augment spatial perception. The external ear transfer function is altered by variations in the physical dimension of the external ear either due to individual differences or due to mechanical obstructions such as blockages, hearing aid placement, perforation of the tympanic membrane, and use of insert earphone. It is significant that any change in the characteristics of the acoustic signal can produce considerable disparity in within- and between-individual responses. The present paper examines published studies on sound pressure transfer function provided by the external ear in humans.