PRESSURE TRANSFER-FUNCTION AND ABSORPTION CROSS-SECTION FROM THE DIFFUSE FIELD TO THE HUMAN INFANT EAR CANAL

The diffuse-field pressure transfer function from a reverberant field to the ear canal of human infants, ages 1, 3, 6, 12, and 24 months, ha s been measured from 125-10700 Hz. The source was a loudspeaker using pink noise, and the diffuse-field pressure and the ear-canal pressure were simultaneously measured using a spatial averaging technique in a reverberant room. The results in most subjects show a two-peak structu re in the 2-6-kHz range, corresponding to the ear-canal and concha res onances. The ear-canal resonance frequency decreases from 4.4 kHz at a ge 1 month to 2.9 kHz at age 24 months. The concha resonance frequency decreases from 5.5 kHz at age 1 month to 4.5 kHz at age 24 months. Be low 2 kHz, the diffuse-field transfer function shows effects due to th e torsos of the infant and parent, and varies with how the infant is h eld. Comparisons are reported of the diffuse-field absorption cross se ction for infants relative to adults. This quantity is a measure of po wer absorbed by the middle ear from a diffuse sound field, and large d ifferences are observed in infants relative to adults. The radiation e fficiencies of the infant and the adult ear are small at low frequenci es, near unity at midfrequencies, and decrease at higher frequencies. The process of ear-canal development is not yet complete at age 24 mon ths. The results have implications for experiments on hearing in infan ts.