Artificial heads versus miniature microphones for measuring active noise-reduction hearing protector performance

Abstract

The results of sound attenuation measurements on hearing protectors with head and torso simulators (HATSs) are quite encouraging if suitable corrections for the bone conduction and the occlusion effect are applied. Yet, the real-ear-at-threshold (REAT) method is still the standardized and most often used procedure to get appropriate measures for the protection provided by passive earmuffs and passive earplugs. With the development of active noise reduction (ANR) hearing protectors, however, the REAT method fails because of the background noise generated by the electronic components of the devices. Furthermore, the limits and the efficiency of such devices cannot be tested with sound-pressure levels near the hearing threshold. Thus there is an urgent need for using either HATSs or probe microphones on humans for the measurement of the ANR performance of a hearing protection device. Attempts to determine the effective attenuation with a combination of REAT and artificial head measurements will be compared with the results of microphone in real ear (MIRE) measurements for several commercially available ANR systems, including noise cancelling headphones. Aspects of validity and uncertainty of the various procedures, as well as practical relevance and ethical considerations, will be discussed.