This International Standard specifies a subjective method for measuring sound attenuation of hearing protectors at the threshold of hearing. The method is a laboratory method designed to yield reproducible values under controlled measurement conditions. The values reflect the attenuating characteristics of the hearing protector only to the extent that users wear the device in the same manner as did the test subjects. For a more representative indication of field performance the methods of ISO/TS 4869-5 may be used. This test method yields data which are collected at low sound pressure levels (close to the threshold of hearing) but which are also representative of the attenuation values of hearing protectors at higher sound pressure levels. An exception occurs in the case of amplitude-sensitive hearing protectors for sound pressure levels above the point at which their level-dependent characteristics become effective. At those sound pressure levels the method specified in this International Standard is inapplicable; it will usually underestimate sound attenuation for these devices. NOTE At low frequencies (below 500 Hz) the sound attenuation may be overestimated by a few decibels as a result of masking caused by physiological noise during the occluded ear tests.