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Pressure transfer function and absorption cross section from the diffuse field to the human infant ear canal
D H Keefe1, J C Bulen, S L Campbell
1School of Music, University of Washington, Seattle 98195.
Insights
The study measured how sound travels to infants
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.
Abstract:
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, has 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 structure in the 2-6-kHz range, corresponding to the ear-canal and concha resonances. The ear-canal resonance frequency decreases from 4.4 kHz at age 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. Below 2 kHz, the diffuse-field transfer function shows effects due to the torsos of the infant and parent, and varies with how the infant is held. Comparisons are reported of the diffuse-field absorption cross section for infants relative to adults. This quantity is a measure of power absorbed by the middle ear from a diffuse sound field, and large differences are observed in infants relative to adults. The radiation efficiencies of the infant and the adult ear are small at low frequencies, near unity at midfrequencies, and decrease at higher frequencies. The process of ear-canal development is not yet complete at age 24 months. The results have implications for experiments on hearing in infants.