Measurement of the real-ear attenuation of hearing protectors according to the South African Standard SABS 572 1973

Abstract

In general current national standards for the measurement of the real-ear attenuation of hearing protectors involve the use of a real-ear attenuation at threshold, or REAT method. One of the few which does not is the South African Standard SABS 572 1973. This involves use of a loudness balance method by means of which, since it is performed at supra-threshold levels, one avoids some of the problems associated with REAT methods. The values of attenuation generated by this method have been reported to be substantially lower than those produced by not only REAT methods but also previous loudness balance methods. The nature of these discrepancies was not fully explained by the authors of the standard and therefore a further investigation of this method was felt to be necessary. Accordingly, a series of measurements have been performed in accordance with the instructions contained in SABS 572 1973. The results of these experiments are of the same character as those described by the authors of the standard. Attenuation values were generated which were appreciably less than those produced by REAT methods. Efforts were made to determine the cause of the discrepancies. Evidence from the literature together with the results from a subsidiary experiment has demonstrated that SABS 572 1973 is probably in error. There is an implicit assumption in the standard that the attenuation of a circumaural protector is substantially augmented by the introduction of an insert earphone into the ear beneath the protector cap. This view was not corroborated by the experimental evidence and it is concluded that SABS 572 1973 requires major modification.