The external ear sound pressure level transformation in infants

Some preliminary findings obtained in a study of the acoustic characteristics of the external ears of infants are reported. A technique was developed for positioning the inlet of a probe-tube microphone in the lateral-half of the ear canals of sleeping infants. A diffuse sound field (spectral density approximately 42 dB SPL) was introduced and the microphone output recorded. Free-field-to-ear canal sound pressure level transformations were determined for infants ranging in age from a few days old to 36 months. Representative transformations are presented, and these vary systematically with the age of the child. The resonance frequency of the external ear is high in newborns and declines exponentially with age. The asymptotic value (approximately 2700 Hz) appears to be reached during the second year of life. [Work supported by NIH-NINCDS.]