Objective: Our objective was to obtain reliable threshold measurements without a sound booth by using a passive noise-attenuating hearing protector combined with in-ear 1/3-octave band noise measurements to verify the ear canal was suitably quiet.
Design: We deployed laptop-based hearing testing systems to Tanzania as part of a study of HIV infection and hearing. An in-ear probe containing a microphone was used under the hearing protector for both the in-ear noise measurements and threshold audiometry. The 1/3-octave band noise spectrum from the microphone was displayed on the operator's screen with acceptable levels in grey and unacceptable levels in red. Operators attempted to make all bars grey, but focused on achieving grey bars at 2000 Hz and above.
Study sample: 624 adults and 197 children provided 3381 in-ear octave band measurements. Repeated measurements from 144 individuals who returned for testing on three separate occasions were also analysed.
Results: In-ear noise levels exceeded the maximum permissible ambient noise levels (MPANL) for ears not covered, but not the dB SPL levels corresponding to 0 dB HL between 2000-4000 Hz. In-ear noise measurements were repeatable over time.
Conclusions: Reliable audiometry can be performed using a passive noise-attenuating hearing protector and in-ear noise measurements.