An Investigation of the Attenuation Provided by the Surefire EP3 Sonic Defender™ Earplug


  1. Abel, S.M.
  2. Nakashima, A.
Corporate Authors
Defence R&D Canada - Toronto, Toronto ONT (CAN)
The sound attenuation provided by the Surefire EP3 Sonic Defender™ earplug was determined in five males and five females. According to the manufacturer, an orifice in the plug allows safe sound levels to pass while lowering potentially harmful levels above 80 dBA from impulse noise by 35 dB. With the orifice closed the device performs like a conventional level-independent earplug. In each subject, hearing thresholds were measured at nine one-third octave noise band centre frequencies with the ears unoccluded and fitted with the Surefire EP3 with the orifice open and closed. Attenuation was defined as the difference between the protected and occluded thresholds. With the orifice closed attenuation increased non-monotonically from 14.5-31.0 dB from 0.125 kHz to 8 kHz. A decrease to 19.1 dB was evident at 4 kHz. With the orifice open attenuation increased from 4.4-27.0 dB with a decrease to 16.6 dB at 4 kHz and 6.3 kHz. The greatest differences due to mode of operation (9-10 dB) were observed at 0.125 and 0.25 kHz. There was no effect of gender of subjects. Comparison with the E-A-R® Combat Arms earplug, which also has modes of operation for continuous and impulse noise indicated that the two devices were similar for the orifice open condition. For the orifice closed condition the Combat Arms earplug provided attenuation of 20.7-40.3 dB, on average 8 dB more than the Surefire EP3. Surefire EP3 attenuation was also compared with insertion loss measurements obtained using an ac

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hearing protection;noise-induced hearing loss
Report Number
DRDC-TORONTO-TR-2008-040 — Technical Report
Date of publication
01 May 2008
Number of Pages
Electronic Document(PDF)

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