Audiometric tests are widely used in Brazil to identify noise induced hearing losses, routine examination to support otolaryngology diagnoses and to design appropriate hearing aids. It can be very complicated to estimate uncertainties in such areas once it involves human sensitivity. In Brazil all audiometric tests shall follow the ISO 8253-1 requirements, which, in turn, refer to ISO Guide 98-3 for the expression of uncertainty in measurement. According ISO 8253-1 seven input quantities should be considered to estimate the uncertainty for hearing threshold level measurements. The contribution due some of those input quantities for total uncertainty was estimated from audiometric data obtained during an experimental investigation involving fifteen subjects, each of them tested six times during three days, in the morning and afternoon. A second trial of measurements was performed in live room with highly absorbent foam placed on all surfaces to reduce the reverberation and also background levels, which remained below ISO requirements. Again each of five subjects were tested six times for repeatability estimation. The last test checked the influence of operator/subject headphone fitting.
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