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Monday, July 8 • 16:10 - 16:30
A COUPLED FINITE ELEMENT/TRANSFER MATRIX METHOD TO SIMULATE THE INSERTION LOSS OF EARPLUGS IN AN ACOUSTIC TEST FIXTURE

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Acoustic test fixtures (ATFs) can be used to measure the insertion loss (IL) of earplugs. Reliable numerical modeling of the occluded artificial ear canal of the ATF could be helpful for optimizing the earplug performance during the design phase. This requires the simulation of the IEC 60318-4 occluded ear simulator which is usually based on the classical lumped parameter model (LPM) or complete 3D numerical model. Lumped models are generally accepted to have inherent frequency limitations and cannot properly deal with the thermal and viscous phenomena in certain areas of the simulator. 3D numerical models based on the finite element (FE) or boundary element method are capable of accurately describing the simulator behavior taking thermo-viscous effects into consideration but many dimensional details related to the published numerical models of the IEC 60318-4 simulator remain unspecified. This study proposes a transfer matrix (TM) model of the IEC 60318-4 simulator whose geometry is determined using Computed Tomography scan images. The specific acoustic impedance of certain elements in the simulator model is deduced using the low reduced frequency (LRF) model which has been proved satisfactory to account analytically for thermo-viscous energy losses. The TM model is validated using a 3D FE model of the simulator based on the same geometric dimensions. It is then coupled to a 2D axisymmetric FE model of an ATF ear canal occluded or not by a silicone earplug to simulate the earplug IL. The coupled FE/TM method is found to provide satisfactory IL prediction compared to a complete 3D FE model of the corresponding system. The proposed TM model is also shown to better capture the simulator behavior compared to the classical LPM.


Monday July 8, 2019 16:10 - 16:30 EDT
Outremont 4
  T06 Industr. and occup. Noise & vib., SS01 Hearing protection