Assessment of otoacoustic emission probe fit at the workfloor using integrated calibration procedure

Invited paper

Vincent Nadon

Gent Universiteit

Wednesday 3 june, 2015, 10:00 - 10:20

0.4 Brussels (189)

<latex>To evaluate and improve the effectiveness of personal hearing protection at the workfloor, an in-field measurement procedure of otoacoustic emissions (OAE) has been developed and validated. Anyhow, unsupervised evaluation of OAE probe placement during the work shift is an important challenge for in-field OAE measurement. In this regard, proper OAE probe fit in the ear canal is a major concern in order to provide optimal ambient noise isolation and to ensure that OAE stimuli levels are precisely calibrated at the eardrum. Stimuli sound pressure level (SPL) at eardrum reference point (ERP) can be established using the ear canal transfer function, probe microphone and receivers during the calibration procedure. SPL calibrated at ERP should account for individual differences in probe placement. Previous work shows that an important characteristic of this transfer function is the residual ear canal length between the OAE probe and eardrum. As a result, probe insertion depth and related probe noise isolation can be estimated by measuring this transfer function. In the following study, a lumped elements model of an occluded ear canal is used; first, to analyze the effects of probe insertion depth on the ear canal transfer function. Second, to validate the proposed method by comparing the model's transfer functions with those estimated during experiments with an OAE probe and tube setup. Afterwards, the probe's passive noise isolation is calculated for different insertion depth by measuring the SPL inside and outside the occluded tube. Finally, the relationship between the probe's noise isolation, occluded ear canal transfer function and residual ear canal length is established. This proposed approach could assess the probe fit \emph{in situ} and solve problems of unsupervised evaluation of probe placement by automatically warning the wearer of a shallow fit.</latex>

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