Frequency compensation for in-ear noise dosimetry

Abstract

Personal noise dosimeters (PNDs) are used in the prevention of noise induced hearing loss (NIHL) by monitoring noise exposure. Exposure of a worker is typically estimated by measuring the noise level at the shoulder location and subtracting the estimated protection provided by any worn hearing protection devices. Current noise dosimeters in the marketplace are deficient because the noise level at the shoulder does not necessarily represent the noise exposure in the ear canal due to shadowing, canal resonances and other acoustical phenomena. Moreover, workers often deliberately insert earplugs to shallow canal depths to better hear their environments, and earmuff attenuation is inconsistent due to variations in head geometry. Thus, the estimated hearing protection is often in error. In-ear personal noise dosimeters (iPNDs) can solve these problems because they incorporate a microphone within a hearing protection earplug that measures the actual noise level in an ear canal. However, the acoustics of the in-ear measurement are quite different compared to the shoulder measurement, and in-ear measurements must be frequency compensated to achieve valid results. This paper discusses in-ear noise dosimetry, why frequency compensation is needed and how to compensate the microphone signal. [This work was funded by a CDC SBIR grant.]