Standard test methods to determine hearing protector attenuation use a real ear at threshold subjective method, where subjects identify when they can just hear test signals in order to establish their threshold of hearing. The threshold of hearing is measured over a range of test frequencies, with and without a hearing protector worn. The difference in threshold (with and without a hearing protector) provides the attenuation; and a group of results from a range of subjects provides a mean result and a standard deviation in each test frequency band.
Systems that measure earplug attenuation for individual wearers are commercially available and the work detailed in this report aimed to assess the performance and test the reliability of two types of available system: objective measurement and subjective equal loudness. Systems were chosen to represent a type of system rather than a specific model of device and because they: were commercially available through leading manufacturers; were designed for use by operators with a minimal level of training or expertise; could be used with a range of earplugs; and were typical of the state of the art.
Both systems investigated were found to have benefits and limitations. A number of recommendations are presented.
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