A procedure, combining objective and subjective techniques, to measure the level-dependent attenuation of electronic amplitude-sensitive earmuffs

Abstract

Electronic amplitude-sensitive earmuffs (EASEs) are hearing protectors designed to provide electroacoustic restoration of ambient sounds at low levels, progressively reduced as the ambient level increases. No standardized procedure is available, at the present time, for assessing the attenuation given by such protectors, at different ambient sound levels. Several possible methods have been examined. The microphone-in-real-ear (MIRE) technique appears interesting but still difficult to be used as a ‘routine’ method. The alternative procedure proposed here allows measuring of the EASEs attenuations on a standardized acoustic test fixture (ATF), at different ambient sound levels and in different frequency bands. The measures are then corrected, using a correction formula which introduces the real-ear attenuation in passive mode (electroacoustic restoration ‘off’). The relevance of this procedure has been checked on five models of EASEs. For a reference, attenuations were measured, in different frequency bands and at different ambient sound levels, by the MIRE technique. On the other hand they were measured by the proposed corrected-ATF procedure. The approximation of the real-ear attenuation by the present corrected ATF method is rather good for all five EASEs, particularly at the higher sound levels: corrected ATF values asymptotically tended to those found using MIRE for the passive mode (MIREPM). If, for practical purposes, MIREPM values were replaced by real-ear attenuation at threshold (REAT) values for the passive mode (REATPM) measured according to ISO 4869-1, the corrected ATF values will then approach those found by REATPM. The procedure proposed here, based on standardized measurements, allows efficient correction of measurements made on ATF, particularly at the higher noise levels, which are the most troublesome for hearing conservation purposes. It can provide an alternative to MIRE measurements for situations in which an alternative technique is preferred.