Effects of hearing protection devices on speech intelligibility and situational awareness – a literature review

This report summarizes our literature review to investigate the effects of hearing protection devices (HPD) on speech intelligibility and situational awareness. This is especially relevant in light of shooting activities being conducted in the Norwegian Armed Forces. Based on our review, we recommend the following:
•For the assessment of speech intelligibility with different HPDs or combinations of HPDs, subjective methods should be used, specifically the HINT method (Hearing in noise test), with the test materials in Norwegian. The type and level of background noise during subjective tests should represent the operational environment for respective users. Using Norwegian HINT lists for subjective tests to determine word recognition scores should be investigated. This may make it easier to compare the results from international institutions that have used other subjective methods for testing the performance on speech intelligibility.•A major aspect of situational awareness is sound source localization. The sound source localization measurements should be carried out in accordance with the ANSI S3.71-2019 Methods for Measuring the Effect of Head-worn Devices on Directional Sound Localization in the Horizontal Plane standard.•Several investigations and experiments show that level-dependent earplugs positively affect noise attenuation and speech intelligibility. The Norwegian Armed Forces should include this type of passive earplugs in their investigation for better hearing protection devices in the high-noise environments.