Currently, the hearing threshold method according to DIN ISO 4869 (1991) is typically used to determine the insulation of hearing protection devices. The subjectively determined insulation values are assumed to be independent of the level, that is, valid for all real life exposure levels. The validity of this assumption was to be objectively tested with the aid of an artificial head measuring system. Four hearing protection devices were exposed to a diffuse sound field at levels of 65, 85, and 105 dB with one-third octave band noise according to DIN ISO 4869, and the effective attenuation values (reduction in noise level provided by the hearing protector measured in dB) were determined. The evaluation of measuring data confirmed that the effectiveness of the examined ear muffs is approximately equal for the different noise levels. In a second step, the attenuation values were compared to the values which were subjectively determined according to DIN ISO 4869. Partially very different courses were observed. If appropriate correction factors are applied, however, the use of the absolutely objective artificial head measuring technique instead of the subjective method according to DIN ISO 4869 seems to be feasible.