What Does Noise Reduction Rating (NRR) Mean?
Noise Reduction Rating (NRR) is the difference between the overall C-weighted sound level of a noise spectrum having equal energy per octave and the resulting A-weighted noise levels under a hearing protection device.
Safeopedia Explains Noise Reduction Rating (NRR)
Noise Reduction Rating is used to evaluate and determine the effictiveness or fit of noise protection equipment for a given work environment. NRR is specifically the measurement, in decibles, of how well hearing protection reduces noise as specified by the Environmental Protection Agency.
The higher the NRR number the greater the noise reduction. While wearing hearing protection your exposure to noise is equal to the total noise level minus the NRR of the hearing protectors in use. For example, if you were exposed to 80db of noise but were wearing earplugs with an NRR of 29, your actual noise exposure would only be 51dB.