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Transmission of High-Amplitude Sound through Leakages of Ill-fitting Earplugs

Haocheng Yu, Krishan K. Ahuja, Lakshmi N. Sankar, Spencer H. Bryngelson

TL;DR

This study addresses sound leakage through ill-fitting earplugs under high sound pressure levels by developing an analytical circular-orifice leak model, validating it with impedance-tube experiments, and examining leakage dynamics via direct numerical simulations with the MFC solver. The work shows that leaks can substantially diminish attenuation (e.g., ${\sim}18$ dB TL reduction at $\mathrm{OISPL}=120$ dB for silicone rubber) and that sealing leaks markedly improves performance, while higher SPLs enhance dissipation through vortex shedding, especially at lower frequencies as explained by Strouhal-number considerations. Three-dimensional simulations further reveal that realistic geometry shifts vortex shedding to the ear canal outlet, confirming significant energy conversion to vorticity as a dominant dissipation mechanism. Collectively, the results highlight the critical role of earplug fit and seal integrity in high-SPL environments and provide a framework for designing earplugs with improved leakage resistance.

Abstract

High sound pressure levels (SPL) pose notable risks in loud environments, particularly due to noise-induced hearing loss. Ill-fitting earplugs often lead to sound leakage, a phenomenon this study seeks to investigate. To validate our methodology, we first obtained computational and experimental acoustic transmission data for stand-alone slit resonators and orifices, for which extensive published data are readily available for comparison. We then examined the frequency-dependent acoustic power absorption coefficient and transmission loss (TL) across various leakage geometries, modeled using different orifice diameters. Experimental approaches spanned a frequency range of 1--5 kHz under SPL conditions of 120--150 dB. Key findings reveal that unsealed silicone rubber earplugs demonstrate an average TL reduction of approximately 18 dB at an overall incident SPL (OISPL) of 120 dB. Direct numerical simulations further highlight SPL-dependent acoustic dissipation mechanisms, showing the conversion of acoustic energy into vorticity in ill-fitting earplug models at an OISPL of 150 dB. These results highlight the role of earplug design for high-sound-pressure-level environments.

Transmission of High-Amplitude Sound through Leakages of Ill-fitting Earplugs

TL;DR

This study addresses sound leakage through ill-fitting earplugs under high sound pressure levels by developing an analytical circular-orifice leak model, validating it with impedance-tube experiments, and examining leakage dynamics via direct numerical simulations with the MFC solver. The work shows that leaks can substantially diminish attenuation (e.g., dB TL reduction at dB for silicone rubber) and that sealing leaks markedly improves performance, while higher SPLs enhance dissipation through vortex shedding, especially at lower frequencies as explained by Strouhal-number considerations. Three-dimensional simulations further reveal that realistic geometry shifts vortex shedding to the ear canal outlet, confirming significant energy conversion to vorticity as a dominant dissipation mechanism. Collectively, the results highlight the critical role of earplug fit and seal integrity in high-SPL environments and provide a framework for designing earplugs with improved leakage resistance.

Abstract

High sound pressure levels (SPL) pose notable risks in loud environments, particularly due to noise-induced hearing loss. Ill-fitting earplugs often lead to sound leakage, a phenomenon this study seeks to investigate. To validate our methodology, we first obtained computational and experimental acoustic transmission data for stand-alone slit resonators and orifices, for which extensive published data are readily available for comparison. We then examined the frequency-dependent acoustic power absorption coefficient and transmission loss (TL) across various leakage geometries, modeled using different orifice diameters. Experimental approaches spanned a frequency range of 1--5 kHz under SPL conditions of 120--150 dB. Key findings reveal that unsealed silicone rubber earplugs demonstrate an average TL reduction of approximately 18 dB at an overall incident SPL (OISPL) of 120 dB. Direct numerical simulations further highlight SPL-dependent acoustic dissipation mechanisms, showing the conversion of acoustic energy into vorticity in ill-fitting earplug models at an OISPL of 150 dB. These results highlight the role of earplug design for high-sound-pressure-level environments.
Paper Structure (19 sections, 12 equations, 26 figures, 3 tables)

This paper contains 19 sections, 12 equations, 26 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Background
  3. Previous Work
  4. Circular Orifice Model of Leaks
  5. Methodology
  6. Acoustic Performance Metrics
  7. Experimental Method
  8. Experimental setup
  9. Transmission Loss of Orifice Plates
  10. Ear Test Articles
  11. Numerical Methods
  12. Compressible Flow Solver
  13. Simulation Configuration
  14. 2D Slit Resonator
  15. Results
  16. ...and 4 more sections

Figures (26)

  • Figure 1: Sketch of (a) the human ear with an earplug inserted in the ear canal and (b) its analogy to a circular orifice opening
  • Figure 2: A layout (not to scale) and specifications of the extended two-sided tube with its data acquisition system. The inner diameter of the tube is $D = 25.4mm$.
  • Figure 3: The processing steps: (a) separating the incident and transmitted pulse from their reflected pulses, (b) applying a Hann window on the separated incident and transmitted pulses, (c) averaging 100 windowed incident and reflected pulses, and (d) using FFT to determine the incident and transmitted power spectral density (PSD), which is used to calculate the TL defined in \ref{['eq:TL_tau']}.
  • Figure 4: The five orifice plates studied in this work.
  • Figure 5: Measured performance of the steel orifice plates (test article #1--5) under $\mathrm{OISPL}=120dB$ for (a) the transmitted pulse in time domain and (b) the transmission loss spectrum compared to the analytical model described in \ref{['ss:analy_model']}.
  • ...and 21 more figures