Sound Pressure Transformation from the Free Field to the Eardrum

Abstract

The sound pressure transformation by the human head and external ear has been the subject of many measurements over a long period of time. The average acoustic properties of the external ear are now established sufficiently well that diverse data can be brought into a common set of reference frames. Data from 10 studies in five countries are presented in terms of eardrum response at eight azimuthal angles as functions of frequency from 0.2 to 12 kHz. Data from the same pool are also presented in terms of azimuthal variations and interaural level differences at 18 frequencies. Where there is lack of agreement between studies, the presentation often indicates the probable causes. A critical examination of all the data leads to self-consistent families of average response at the eardrum position as a function of frequency and angle of incidence in the azimuthal plane. An extension of the method should provide useful estimates of average response at angles of incidence not on the horizontal plane.