In the U.S., hearing protection is sold with a Noise Reduction Rating (NRR) required by the U.S. Environmental Protection Agency.1 The purpose of the NRR is to inform consumers about the potential to reduce hazardous sounds to a level which is safe for the ear of the person using the protection.
Input data to calculate the NRR requires that hearing protection is tested via a method designed to assess the attenuation in the presence of continuous noise, using subjective response of a group of subjects with relatively normal hearing.