The External Ear

Abstract

The external ear protects the eardrum from mechanical damage by providing a narrow and extended entrance to the auditory system. It also transforms the sound field modifying and augmenting the directionality associated with head diffraction and adding substantial acoustic gain at the higher frequencies. These properties are intimately connected with the spatial perception of sound and are of considerable importance in auditory measurements and instrument design. To understand these properties it is useful to divide the acoustic antenna system into its functional components: the head, the torso and the pinna flange (Fig. 1) acting as diffracting bodies, the concha and the earcanal serving as acoustic resonators, and the eardrum providing an acoustic termination. But these components must always be seen as parts of an integrated system for it is the sound pressure transformation from the free field to the eardrum as a function of frequency, direction, and perhaps distance which is most directly linked with monaural and binaural localization and with the overall sensitivity of the hearing system.