When a worker's time-weighted noise exposure exceeds 100 dBA, both earplugs and earmuffs should be worn. How much attenuation a hearing protector provides depends on its characteristics and how the worker wears it. Because a worker may not know how long a given noise exposure will last or what additional noise exposure he or she may incur later in the day, it may be prudent to wear hearing protectors whenever working in hazardous noise. Fortunately, none of these reasons present insurmountable barriers. The best hearing protector is the one that the worker will wear .
Several methods exist for estimating the amount of sound attenuation a hearing protector provides.
The NRR was designed to function as a simplified descriptor of the amount of protection provided by a given device. The formulas used to calculate the NRR are based on the octave-band, experimenter fit, REAT method. The NRR was intended to be used to calculate the exposure under the hearing protector by subtracting the NRR from the C-weighted unprotected noise level. To get around some of the limitations associated with NRR calculations, other methods have been developed for estimating hearing protector performance. Both NRR and the other hearing protector ratings referred to above are based on data obtained under laboratory conditions in which experimenters fit hearing protectors on trained listeners.