The 2002 International Congress and Exposition on Noise Control Engineering Dearborn, MI, USA. August 19-21, 2002 Expandable Earplug With Smart Custom Fitting Capabilities J. Voix and F. Laville Département de génie mécanique, École de technologie supérieure 1100 Notre-Dame Ouest Montréal, Québec, H3C 1K3, CANADA Abstract For hearing protection to be made effective, the research needs established by NIOSH (National Institute for Occupational Safety and Health) are to find a way for workers to be individually fitted and to offer them increased comfort and the ability to hear speech and warning signals. To address these issues, a new concept has been developed; a re-usable earplug that is custom-fitted thanks to silicon injection between a hard core and a soft expendable envelope. A miniature bore in the hard core is used to determine the sound pressure level difference across the earplug and for real time monitoring of the acoustic seal during the injection process until an adequate fit has been reached. Another benefit of this measuring capability is the development of a field method to estimate the noise attenuation obtained by such expandable earplugs as worn in the workplace. This estimation uses a statistical approach to link subjective attenuation with objective measurement of the Noise Reduction. Further developments include inserting filtering elements in the earplug; passive filters for selective sound attenuation and active filters to let the worker hear speech and warning signals. 1. Introduction The NIOSH (National Institute for Occupational Safety and Health) has gathered all its recent data and has established research needs for new Hearing Protection Devices as follow: "[...] The noise attenuation of hearing protectors as they are worn in the occupational environment is usually quite different from that realized in the laboratory. The manufacturer's labeled NRRs [Noise Reduction Ratings] (which are currently used by OSHA [Occupational Safety and Health Administration] in determining compliance with the PEL [Protected Exposure Level] when engineering controls are being implemented or are not feasible) usually do not reflect actual experiences. Thus a pressing need exists for a laboratory method to estimate the noise attenuation obtained with hearing protectors worn in the field. Field research is now