Norin, Emanuel, and Letowski (2011) report that passive, level-dependent earplugs (combat arms earplugs and Sonic II earplugs) provided word recognition scores similar to scores obtained without earplugs. The authors performed audiometric evaluations in quiet and in two background noise situations (multitalker noise and military vehicle noise). Across different levels of attenuation, multiple noise environments and multiple signal-to-noise ratios (+10, 0 , -10 dB), Norin and colleagues determined that the single most important factor related to word recognition scores was the signal-to-noise ratio (SNR).
The authors concluded that, “individuals subjected to high-level impulse noise should be able to use passive, level-dependent earplugs to protect their auditory system from noise-induced damage without noticeably compromising speech communication.”
For More Information, References, and Recommendations
Norin JA, Emanuel DC, Letowski TR. (2011) Speech Intelligibility and Passive, Level-Dependent Earplugs. Ear & Hearing, 32(5):642-649.
Wu CC, Young YH. (2009) Ten-Year Longitudinal Study of the Effect of Impulse Noise Exposure from Gunshot on Inner Ear Function. International Journal of Audiology (48)9:655-660.