Attenuation AND awareness? : Designing a method for measuring accuracy and certainty of sound identification when wearing a HPD

Abstract: Noise pollution is widespread in today’s society, from traffic to industrial sources, and many people are confined to unhealthy acoustic environments through their employment. When noise cannot be eliminated at the sound source, the protective measure is usually to equip the employee with hearing protection devices (HPDs), e.g. earmuffs, that attenuates the noise. Applying excessive attenuation can render the wearer disconnected from her acoustic environment and present risks and social isolation. HPDs using level-dependent function (LDF) uses ambient microphones together with a signal processing unit and internal loudspeakers to achieve attenuation flexibility – if ambient noise is low, the loudspeakers can amplify the sound to combat an excessive passive attenuation of the HPD, and if ambient noise is high this amplification is decreased to maintain healthy sound levels. Appropriate levels of attenuation allows the user to detect ambient sounds which contributes to the their situational awareness. Besides attenuating the sounds however, HPDs does change the spectral content of the sound which may complicate the ability to identify them. This thesis has focused on exploring the human ability to identify sounds, design a method for measuring this ability, implement it and evaluate its result and the method itself. The thesis has been conducted in collaboration with 3MTM PeltorTM and was intended to evaluate the effect of earmuffs with LDF on the ability to identify sounds in a process industry soundscape. The progression of the thesis was structured within the Double Diamond process, where literature reviews, benchmarking and workshops informed the research and resulted in a method design that was analyzed using a repeated measures ANOVA based on empirical data from 16 participants. Surprisingly, the results showed no statistically significant advantage from wearing a HPD using LDF, as opposed to no LDF, in the user accuracy or certainty in sound identification. The reasons for this are discussed with a focus on evaluating the usefulness of the designed method in future efforts to develop HPDs that afford reliable sound identification.