RE-DETERMINATION OF THE THRESHOLD OF HEARING UNDER FREE-FIELD AND DIFFUSE-FIELD LISTENING CONDITIONS

The data for the reference threshold of hearing under free-field and d iffuse-field listening conditions as specified in the International St andard ISO 226 from 1987 were compiled during measurements over a peri od of several years at the National Physical Laboratory, England, in t he mid-fifties. In order to re-determine the threshold data, five inst itutes from Denmark, Germany and Japan recently combined in a joint pr oject with each institute carrying out extensive investigations. Free- field data were determined from hearing threshold measurements, wheres diffuse-field data were calculated from free-field data and random in cidence characteristics of human heads. Fortunately, the results of th ese studies are quite consistent and have allowed new reference data i n a frequency range slightly extended towards high frequencies to be c alculated. A revised version of ISO 226, now being assigned ISO 389-7 as part of the standard series specifying the reference zero for the c alibration of audiometric equipment, has been submitted to national st andardization organizations for voting.