This part of ISO 4869 specifies a method for measuring the insertion loss of ear-muff type hearing protectors using an acoustic test fixture. The method is applicable to the investigation of production spreads of performance as part of type approval or certification procedures, and to the investigation of the change of performance with age. It is intended to ensure that ear-muff hearing protector samples submitted for subjective testing of attenuation according to ISO 4869-1 have performances typical of the type. The method specified in this part of ISO 4869 is not applicable as the basic test for type approval. Performance data obtained by this method are not intended to be quoted as representing the real-ear sound attenuation of an ear-muff, nor the protection provided by the ear-muff. For the testing of certain ear-muffs (such as those attached to safety helmets, or those with contoured ear-cups or ear-cushions, or supra-aural ear-muffs), the procedure described in this part of ISO 4869 might need to be modified.