Individual in situ calibration of in-ear noise dosimeters

Abstract

The noise exposure of a given individual is commonly assessed using conventional measurement tools such as sound level meters or personal noise dosimeters. While generally effective, the underlying techniques only provide information about the ambient noise levels, and fail to account for the attenuation provided by potential hearing protectors being worn. Assuming that the risk of hearing loss is directly related to the sound pressure levels (SPLs) at the eardrum, in-ear noise dosimetry (IEND) is a promising approach to continuously monitor an individual’s noise exposure inside the ear and better predict the energy that ultimately reaches the inner ear. Current IENDs, however, do not allow direct measurement of eardrum SPLs, as the in-ear microphone is typically located at a certain distance from the tympanic membrane. Furthermore, because of the inter-individual variability in the earcanal’s size and geometry, the correction to convert such distant measured values to the eardrum may be significantly different between two individuals wearing the same IEND. This paper proposes a personal in situ calibration procedure to identify the appropriate acoustical corrections for IEND measurements that aim to assess an individual’s noise exposure at the eardrum. A computational method, together with prototypes, were developed using data collected on human test-subjects and simulation tools. Preliminary results obtained with the developed instrumentation suggest that the proposed method can effectively be used in open (unprotected) ears, ears occluded by earplugs, or ears covered with earmuffs.