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Improving low-frequency attenuation of passive earplugs using Helmholtz resonators
Kévin Carillo1, Franck Sgard1, Olivier Dazel2
1Institut de recherche Robert-Sauvé en santé et en sécurité du travail (IRSST), Montréal, Québec, Canada.
The Journal of the Acoustical Society of America
|April 28, 2026
Summary
New meta-earplugs significantly improve low-frequency noise reduction by controlling sound wave reflections. This passive design enhances hearing protection, especially in noisy environments, by up to 15 dB.
Area of Science:
- Acoustics
- Materials Science
- Audiology
Background:
- Passive earplugs are crucial for preventing noise-induced hearing loss but struggle with low-frequency attenuation.
- Limited effectiveness stems from inconsistent use, poor fit, and inherent acoustic properties, especially for low frequencies.
- Enhanced low-frequency attenuation is vital for better overall hearing protection and improved sound quality.
Purpose of the Study:
- To investigate the impact of the reflection coefficient on low-frequency noise reduction in passive earplugs.
- To explore passive design strategies for optimizing low-frequency attenuation.
- To assess the efficacy of meta-earplugs with Helmholtz resonators for enhanced low-frequency noise reduction.
Main Methods:
- Developed an analytical noise reduction (NR) model to determine conditions for maximum attenuation.
- Designed and tested meta-earplugs featuring three Helmholtz resonators.
- Evaluated performance using an acoustic test fixture and human participants.
Main Results:
- Achieved up to 15 dB increase in low-frequency attenuation (below 1 kHz) by inducing anti-phase or quadrature-phase reflections.
- Demonstrated that this passive strategy maintains effectiveness even with moderate acoustic leakage.
- Meta-earplugs showed significant potential for enhancing low-frequency noise reduction.
Conclusions:
- Optimizing the reflection coefficient at the earplug's medial surface is key to enhancing low-frequency noise reduction.
- Passive meta-earplugs with Helmholtz resonators offer a promising solution for more effective and robust hearing protection.
- This approach improves overall hearing protection and can mitigate the occlusion effect.
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