The acoustic properties of the infant ear. A preliminary report.

This is a preliminary report about the acoustic characteristics of the external ears of infants. A technique was developed to insert a probe tube that is attached to a miniature microphone into the external auditory canals of sleeping infants. The inlet to the microphone was positioned in the lateral half of the external auditory canal. A diffuse sound field (spectral density of approximately 45 dB SPL) was introduced. The microphone output was recorded, and its Fourier Transform was computed. Diffuse-field-to-ear canal sound pressure level transformations were determined for infants ranging in age from newborn to 37 months. Representative sound pressure level transformations are presented. These are shown to vary systematically with the age of the child. The resonance frequency of the external ear is high in the newborns and declines with age. The asymptotic value (approximately 2,700 Hz) is reached during the second year of life. These findings have potential implications for fitting hearing aids on infants and children.