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Acoustic effects in in-the-ear hearing aid response: results from a computer simulation
1Siemens Hearing Instruments, Inc., Piscataway, New Jersey.
Ear and Hearing
|June 1, 1988
Summary
Computer simulations show that ear canal size and eardrum impedance affect in-the-ear hearing aid sound levels but not frequency response shape. Vented hearing aids have complex responses, especially at high frequencies due to feedback.
Area of Science:
- Audiology
- Acoustics
- Biomedical Engineering
Background:
- Hearing aid performance is influenced by device design and individual ear acoustics.
- In-the-ear (ITE) hearing aids require precise fitting due to their placement within the ear canal.
Purpose of the Study:
- To investigate the impact of ear canal size, eardrum impedance, and vent characteristics on ITE hearing aid frequency response using computer simulation.
- To differentiate the effects of these parameters on vented versus unvented hearing aid performance.
Main Methods:
- A computer simulation model was developed to represent an ITE hearing aid.
- Simulations were run to analyze the effects of varying ear canal dimensions, eardrum impedance magnitudes, and vent size/damping.
- The acoustic output at the eardrum was analyzed for different simulated ear canal and hearing aid configurations.
Main Results:
- For unvented ITE hearing aids, changes in ear canal size and eardrum impedance primarily altered the overall sound pressure level at the eardrum, with minimal impact on the frequency response shape.
- For vented ITE hearing aids, vent size predictably influenced low-frequency response.
- Vented instruments exhibited significant and sometimes unexpected high-frequency response alterations due to acoustic feedback loops originating from the vent.
Conclusions:
- Ear canal acoustics and eardrum impedance are critical factors influencing the overall gain of unvented ITE hearing aids.
- Vent design in ITE hearing aids introduces complex acoustic interactions, particularly affecting high-frequency response and necessitating careful consideration in hearing aid fitting and design.
- Computer simulations provide a valuable tool for understanding the intricate relationship between ear canal characteristics, hearing aid design, and acoustic output.