ISO 4869-1:1990 PDF

Specifies a method for measuring sound attenuation at the threshold of hearing. The procedure is designed to yield values close to the maximum attenuation which are not normally attained under field conditions. The values reflect the attenuating characteristics only to the extent that users wear the device in the same manner as did the test subjects. Data are collected at low sound pressure levels but which are also representative of the values at higher sound pressure levels.