Sound attenuation from earmuffs and earplugs in combination: maximum benefits vs. missed information.
BACKGROUND
Noise levels from military aircraft range from 100-130 dBA. Peak pressure levels from large caliber weapons may reach 180 dB SPL. To protect against hearing loss, individuals are encouraged to wear double hearing protection. This study determined ways to maximize benefit.


METHODS
Hearing thresholds from 0.25-8 kHz and consonant discrimination were assessed in normal-hearing subjects with ears unoccluded and fitted with highly rated earmuffs and earplugs, singly or in combination. The earplugs were available in two sizes. Selection was based on best fit. Attenuation values were derived from the threshold measurements.


RESULTS
With the muff, plug, and muff and plug in combination, thresholds ranged from 35-48 dB SPL, 40-55 dB SPL, and 44-66 dB SPL, respectively, across the frequencies tested. The combination (without regard to size of plug) resulted in attenuation values of 38-54 dB. With the smaller of the two plugs, low-frequency values as high as 53-61 dB were realized. Consonant discrimination decreased by 6-8% with the devices worn singly and by 22% with the devices in combination, relative to unoccluded listening.


CONCLUSIONS
Sufficient low-frequency attenuation may be achieved with muffs and plugs in combination to prevent hearing loss from operational noise. Attenuation may be maximized by choosing a smaller earplug to achieve a better fit. Possible downsides are reduced detection of warning sounds and speech intelligibility. To be heard warning sounds should surpass protected thresholds by at least 5 dB. Choosing devices which provide somewhat less attenuation may be necessary to preserve communication capability.
Abel
Sharon M
SM
Defence Research and Development Canada, Toronto, Ontario, Canada. Sharon.abel@drdc-rddc.gc.ca
Odell
Patricia
P
D000328:Adult; D000337:Aerospace Medicine; D001309:Auditory Threshold; D004430:Ear Protective Devices; D005260:Female; D006309:Hearing; D006317:Hearing Loss, Noise-Induced / Q000517:prevention & control; D006801:Humans; D008297:Male; D008889:Military Personnel; D009784:Occupational Diseases / Q000517:prevention & control; D012737:Sex Factors; D013016:Sound