DOSIMETRY MEASUREMENTS USING A PROBE TUBE MICROPHONE IN THE EAR CANAL

Federal and international standards recommend use of microphone placem ent either on or in the vicinity of the shoulder for dosimetry to mini mize deviations from the undisturbed sound field. Probe microphone mea surements from the ear canal were compared to shoulder and chest measu res in order to investigate the validity of current dosimetry methodol ogies. Six subjects were monitored in an industrial setting. As expect ed, ear-canal levels exceeded other measures for all subjects. Shoulde r and chest measures showed very low intersubject variability whereas ear-canal measures resulted in large intersubject variability. The ear -canal methodology has the potential to identify individuals whose ext ernal ear gain exceed the mean, putting them at increased risk of nois e-induced permanent threshold shift (NIPTS). It is proposed that overa ll external ear pressure gain be used as an index to adjust exposure l evels when predicting NIPTS using ISO 1999. A normative database of ex ternal ear pressure gain was constructed from 30 ears for this purpose .