Method to measure the effect of acoustic leaks on active noise reduction device performance

Abstract

Passive hearing protection (HP) systems are designed to reduce the level of noise at the ear. Passive HP typically excel in attenuating mid- to high-frequency noise. Active noise reduction (ANR) has the potential to provide additional attenuation of low-frequency noise. There are documented reports describing unwanted sound being generated by ANR systems if an acoustic leak is present. The objective of this effort was to develop a method to measure the performance of ANR devices with and without the introduction of an acoustic leak. A number of ANR earcups were selected for this study. Data were collected with an artificial ear and a flat base plate in a noise environment that ranged from 65–115 dB SPL. Wedges, designed in-house, created a consistent acoustic leak that ranged in size from 1–2 mm in radius. The results revealed that some ANR earcups provided high levels of protection when the earcup was well-sealed; however, when an acoustic leak was introduced, the earcups became unstable and generated noise in the earcup. This instability was not seen in all ANR devices. The outcome of these measurements solidified the need for a method to measure ANR device performance when acoustic leaks are introduced.