The degree of protection (attenuation) given by hearing protection devices (HPDs) such as earplugs, earmuffs, and canal caps is generally much less in actual use than in laboratory certification tests upon which HPD ratings are based. Also, the attenuation varies so greatly between individuals that the amount of protection provided to any particular individual is almost completely unknown. As a result, underprotection of workers exposed to high noise levels can often only be detected by subsequent measurement of their hearing loss. Procedures which can readily be used to assess field performance of HPDs would be very useful for worker training and hearing conservation program assessment. The one method currently in use is only applicable to earplugs, shows considerable variance from the standard method, and must be done in the quiet environment of an audiometric test booth. A new procedure for measuring HPD attenuation is proposed which may be done in moderately noisy environments and could be used for any sort of hearing protector or combination of HPDs. It is a loudness balance technique in which one sound is delivered to the inner ear by a bone- conduction transducer and another sound is delivered externally to the ear and the HPD. By balancing the loudness of the two sounds both with and without the HPD, the attenuation of the HPD may be directly calculated. Preliminary results indicate that it is a reproducible technique which gives measurements comparable to the standard methods. The proposed research is intended to develop procedures and instrumentation necessary to use this new technique as an alternative method of HPD attenuation measurement. The method will also be compared to the commonly used procedures for both laboratory and field measurements. A variety of different types of HPD will be evaluated using the procedure to demonstrate its usefulness in actual practice and to provide information on any defects and limitations of the method.
