Development of laboratory-based test methods for the comparative evaluation of performance of advanced hearing protection devices

Standard acoustic test methods may not fully capture the performance characteristics of advanced passive and active hearing protection devices. Development of new laboratory-based test methods with the ability to discriminate between the performance characteristics of these devices, such as level-dependent or nonlinear effects, without the use of human subjects was undertaken. Measurements of hearing protection device performance with respect to signal quality, sound localization, self-noise, and impulse response were performed. Signal quality and sound localization were both tested using a compact 3D positioning apparatus which gave us directivity information without the use of human subjects or a large hemispherical test fixture. A sound isolation box was used not only for self-noise but also for impulse response measurements. Results of the impulse testing were compared to freefield shock tube results to ensure consistency among methods. This new evaluation methodology, when performed on an array of advanced hearing protection devices, can provide supplemental or alternative performance data for the relative comparison of devices under test. The results allow for distinction between devices based on preferred characteristics, for example, low self-noise and good signal quality favored over better impulse protection. [Research supported by US Army Natick Soldier Research, Development, & Engineering Center.]