Pressure transfer function and absorption cross section from the diffuse field to the human infant ear canal

Area of Science:

• Acoustics
• Bioacoustics
• Human Physiology

Background:

• Understanding how sound reaches the infant ear is crucial for accurate hearing assessments.
• Previous research has not fully characterized the diffuse-field pressure transfer function in developing human infants.
• Infant hearing development involves significant anatomical changes affecting sound perception.

Purpose of the Study:

• To measure the diffuse-field pressure transfer function (DFPTF) in infants aged 1 to 24 months.
• To analyze the development of ear canal and concha resonances.
• To compare sound absorption and radiation efficiency in infant ears versus adult ears.

Main Methods:

• Simultaneous measurement of diffuse-field and ear-canal pressure using pink noise in a reverberant room.
• Spatial averaging technique applied to infants (1, 3, 6, 12, 24 months) and comparison with adults.
• Frequency range analyzed: 125 Hz to 10700 Hz.

Main Results:

• A two-peak structure (2-6 kHz) was observed, attributed to ear-canal and concha resonances.
• Ear-canal resonance frequency decreased from 4.4 kHz (1 month) to 2.9 kHz (24 months).
• Concha resonance frequency decreased from 5.5 kHz (1 month) to 4.5 kHz (24 months).
• Significant differences in diffuse-field absorption cross-section were found between infants and adults.
• Infant ear development was incomplete at 24 months.

Conclusions:

• Infant ear canal and concha resonances change significantly during the first 24 months of life.
• Infant ears differ from adult ears in sound absorption from diffuse fields.
• These findings have critical implications for designing and interpreting infant hearing experiments.