scope:

This Technical Specification specifies a method for measuring noise reduction of passive hearing protectors at the threshold of hearing. The method is designed to provide estimates of the noise reduction obtained by typical groups of users in real-world occupational settings, who may lack the training and motivation to wear hearing protectors in an optimum manner.
The principle of the test method is to measure the difference in hearing threshold with and without wearing a hearing protector. This difference between the thresholds constitutes the noise reduction. The measurement is done twice on a given number of test subjects.