Noise attenuation performance of deep-insert custom earplugs under single and double hearing protection

This paper evaluates various aspects of noise attenuation performance of deep-insert custom earplugs (DICEPs). Different from traditional custom earplugs, the DICEPs refer to solid earplugs that are custom-manufactured from ear impressions and fit deeply into earcanals of individual users, reaching or passing the second bend of the earcanal. The DICEP was recently developed to provide more reliable hearing protection performance for personnel working in extremely hazardous noise environments. In this paper, a review of prior literature regarding hearing protector performance was given to illustrate the need for performance evaluation on laboratory and field attenuation of DICEP devices. Real-Ear Attenuation at Threshold (REAT) measurements were used to evaluate noise attenuation levels of the DICEP when used alone as single hearing protection (SHP), and in combination with a circumaural earmuff as double hearing protection (DHP). It was experimentally determined that the mean attenuation levels of the DICEP SHP and DICEP DHP systems ranged from 37 to 45 dB and 38 to 48 dB across one-third octave bands spanning from 125 Hz to 8 kHz with NRRs of 29 dB and 32 dB, respectively. Furthermore, the performance consistency for multiple insertions and stability against kinetic activities after the initial insertion of the DICEP SHP and DHP systems were also investigated. Statistical analyses of the test data showed that the DICEP noise attenuation performance was consistent in both SHP and DHP configurations, despite variations in user experience level, fitting protocol and fitting iteration. In addition, the DICEP performance was also observed to be highly stable against jaw and whole-body activities that may be required by users during continuous use in the field.