What is SNR?
SNR (Single Number Rating) is a simplified noise reduction factor. It is usually expressed as a single number indicating the attenuation that a hearing protector can provide. This value is used in determining the effectiveness of hearing protectors.
Using the SNR method to select hearing protectors
The SNR method is used wherever the sound level meter contains a "C" weighting filter and octave band readings cannot be taken. It makes it possible to predict the noise level when determining the continuous sound pressure level ("C").
LCeq - SNR = LAeq
For example, if the SNR is 19 and LCeq is 90, your total would be 90 - 19 = 71 dB.
The HSE recommends allowing 4dB for real-world factors, so you can assume that the hearing protector you choose will produce 75dB at the ear.