Verifying the attenuation of earplugs in situ: Method validation using artificial head and numerical simulations

The use of in situ measurements of hearing protectors' (HPD's) attenuation following the microphone in real ear (MIRE) protocol is increasing. The attenuation is hereby calculated from the difference in sound levels outside the ear and inside the ear canal behind the HPD. Custom-made earpl...

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Bibliographic Details
Published in:The Journal of the Acoustical Society of America 2008-08, Vol.124 (2), p.973-981
Main Authors: Bockstael, Annelies, de Greve, Bram, Van Renterghem, Timothy, Botteldooren, Dick, D'Haenens, Wendy, Keppler, Hannah, Maes, Leen, Philips, Birgit, Swinnen, Freya, Vinck, Bart
Format: Article
Language:English
Subjects:
Acoustics
Computer Simulation
Ear Canal - anatomy & histology
Ear Protective Devices
Equipment Design
Exact sciences and technology
Fundamental areas of phenomenology (including applications)
Head - anatomy & histology
Humans
Models, Anatomic
Models, Biological
Noise - prevention & control
Noise: its effects and control
Physics
Pressure
Reproducibility of Results
Signal Processing, Computer-Assisted
Sound Spectrography
Tympanic Membrane - anatomy & histology
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Summary:The use of in situ measurements of hearing protectors' (HPD's) attenuation following the microphone in real ear (MIRE) protocol is increasing. The attenuation is hereby calculated from the difference in sound levels outside the ear and inside the ear canal behind the HPD. Custom-made earplugs have been designed with an inner bore that allows inserting a miniature microphone. A thorough understanding of the difference, henceforth called transfer function, between the sound pressure of interest at the eardrum and the one measured at the inner bore of the HPD is indispensable for optimizing the MIRE technique and extending its field of application. This issue was addressed by measurements on a head-and-torso-simulator and finite difference time domain numerical simulations of the outer ear canal occluded by an earplug. Both approaches are in good agreement and reveal a clear distinction between the sound pressure at the MIRE microphone and at eardrum, but the measured transfer functions appear to be stable and reproducible. Moreover, the most striking features of the transfer functions can be traced down to the geometrical and morphological characteristics of the earplug and ear canal.
ISSN:0001-4966
1520-8524
DOI:10.1121/1.2945709