Hearing protection has to be selected to bring the level at the ear to somewhere between 70 and 80 dB. This selection can be carried out by using one of three methods.
SNR method
By far the easiest and quickest way of selecting suitable hearing protectors. Most hearing protection manufacturers quote a Single Number Rating (SNR) for their products. This is a measure of how well the protector performs. If one measures SPL using the C-weighting on a meter and then subtracts the SNR figure supplied by the Hearing protector supplier, this will give the sound level at the ear of the wearer.
For example, let us say that a particular employee is subjected to a sound level of 95 dB of C-weighted noise. With hearing protection, we will need to reduce the level at his ear to between 70 and 80 dB. So a hearing protector with an SNR of about 20 will give the required level of protection.
Octave Band method
This involves taking measurements at different frequencies and using these to calculate the required protection. Normally only required for complex noise patters. Not recommended other than for noise professionals.
HML method
An easier method than the Octave Band one. One has to take a C-weighted and an A weighted measurement. The Hearing protection manufacturers supplied data for H, M and L is also required. (H, M and L refer to the protection provided at the High, Medium and Low frequencies).
This method is only required if there is significant low frequency component. However this cannot be described as a simple method.
Note: Those wishing to use the Octave Band or the HML method may find the Hearing Selector provided by 3M useful which can be found on One needs to register to use this facility.
