Use of the Zwicker method to predict signal audibility in noise with hearing protection devices

Abstract

Hearing protection devices (HPDs) can decrease perception of acoustic warning signals. Therefore, specific restrictions are given for the use of HPDs in specific danger areas in Germany. For example, up until 1996, German traffic regulation did not permit use of HPDs while steering a vehicle in road traffic. Within investigations carried out in the 1980s, the audibility of track-layer warning signals was examined during exposure to typical noises and when HPDs were worn. For this purpose, differences in audibility were determined on the basis of the Zwicker method (ISO 532, Method B). As a result, a procedure to predict signal audibility with HPDs was available to select appropriate HPDs for specific situations at work. A special procedure to be carried out if HPDs have to be worn in road traffic was published in 1996 in Germany: A list of hearing protectors realizes a preselection; a final perception test at work under operation conditions carried out by the individual employee and the person responsible for safety indicates the suitability of the HPD. Recent investigations on level-dependent HPDs show that the level of signal audibility seems to depend on the transfer characteristic of the level-dependent HPD.