Evaluation of level-dependent performance of in-ear hearing protection devices using an enclosed sound source

Abstract

Hearing protection devices are increasingly designed with the capability to protect against impulsive sound. Current methods used to test protection from impulsive noise, such as blasts and gunshots, suffer from various drawbacks and complex, manual experimental procedures. For example, the use of a shock tube to emulate blast waves typically produces a blast wind of a much higher magnitude than that generated by an explosive, a specific but important inconsistency between the test conditions and final application. Shock tube test procedures are also very inflexible and provide only minimal insight into the function and performance of advanced electronic hearing protection devices that may have relatively complex response as a function of amplitude and frequency content. To address the issue of measuring the amplitude-dependent attenuation provided by a hearing protection device, a method using a compression driver attached to an enclosed waveguide was developed. The hearing protection device is placed at the end of the waveguide and the response to exposure to impulsive and frequency-dependent signals at calibrated levels is measured. Comparisons to shock tube and standard frequency response measurements will be discussed.