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Sound pressure distribution within human ear canals: II. Reverse mechanical stimulation
Michael E Ravicz1, Jeffrey Tao Cheng1, John J Rosowski1
1Eaton-Peabody Laboratory, Massachusetts Eye & Ear, 243 Charles Street, Boston, Massachusetts 02114, USA.
The Journal of the Acoustical Society of America
|May 10, 2019
Summary
Reverse stimulation of the ear canal (EC) reveals complex sound fields near the tympanic membrane (TM). Nonuniform sound modes significantly influence sound pressure, especially at EC natural frequencies, suggesting earplug design can mitigate these effects.
Area of Science:
- Acoustics
- Bioengineering
- Auditory Physiology
Background:
- Understanding ear canal (EC) sound propagation is crucial for auditory research.
- Otoacoustic emissions (OAEs) involve complex sound interactions within the EC.
- Previous studies often focused on forward sound stimulation, limiting understanding of reverse sound dynamics.
Purpose of the Study:
- To investigate the spatial characteristics of sound fields in the human ear canal under reverse-driven conditions.
- To analyze the influence of nonuniform sound modes on sound pressure near the tympanic membrane (TM).
- To explore the impact of EC occlusion on sound field variations and standing wave patterns.
Main Methods:
- Mechanical "in reverse" stimulation of ossicles in human temporal bones to mimic otoacoustic emissions (OAEs).
- High-resolution sound field sampling within the EC (0.5-2 mm spacing) near the TM and along the longitudinal axis.
- Measurements conducted with the EC in both open and occluded states.
Main Results:
- Reverse-driven sound fields near the TM exhibited greater spatial irregularity below 10 kHz compared to forward stimulation, indicating significant nonuniform sound mode contributions.
- These spatial variations were largely confined to approximately 4 mm from the TM.
- Longitudinal sound variations aligned with standing wave patterns, influenced by EC occlusion, and nonuniform components were prominent at EC natural frequencies.
Conclusions:
- Nonuniform sound modes play a significant role in shaping the sound field near the TM during reverse stimulation.
- Sound field variations are primarily localized near the TM, with limited propagation distally.
- Reducing longitudinal sound pressure variations, potentially through earplug design, can minimize transverse sound pressure variations in the EC.
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