ANSI/ASA S12.6-2008
Methods for measuring the real-ear attenuation of hearing protectors

Real ear attenuation testing uses human subjects to assess the performance of a hearing protection device. The results of these tests are published with the model when it is placed on sale and supplied to wearers. This test measures the threshold of hearing – the lowest sound pressure level perceivable by the ear – of ten or twenty human test subjects with and without the hearing protection worn. It is then possible to calculate the performance of the model from these values, expressed as a Noise Reduction Rating (NRR) value.