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This Malaysian Standard specifies a subjective method for measuring Sound attenuation of hearing protectors at the threshold of hearing. The method and procedures are designed to yield values close to the maximum attenuation which are not normally attained under field conditions. This approach has been adopted because the attenuation values tan then be consistently reproduced. The values reflect the attenuating characteristics of the hearing pro- tector only to the extent that users wear the device in the Same manner as did the test subjects.
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 Standard is inapplicable; it will usually underestimate Sound attenuation for these devices.
MS ISO 4869-1:2004 Acoustics - hearing protectors: Part 1: subjective method for the measurement of sound attenuation (ISO 4869-1:1990, IDT)