Assessment of otoacoustic emission probe fit at the workfloor using integrated calibration procedure
Invited paper
Gent Universiteit
Wednesday 3 june, 2015, 10:00 - 10:20
0.4 Brussels (189)
Abstract:
<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>