International cooperation on hearing thresholds and equal loudness contours

The hearing thresholds and the equal loudness contours for free-field exposure describe some of the most fundamental properties of the human hearing. They have been standardized for many years in ISO226. The data in this standard have their origin in Robinson and Dadson's work in the mid-1950's. More recent data have shown systematic deviations from the standardized data, and a full-scale revision of the standard was started. It was soon realized that the hearing threshold could be revised with only minor changes, and a threshold was standardized separately in ISO389-7:1996. For the equal loudness contours, deviations appeared more serious, and it was realized that the scientific background, in particular concerning psychometric methods and modelling of the loudness function, as well as the available data material, had to be evaluated thoroughly, and most likely new data had to be provided. This work would go beyond the usual work of a standardization working group, and a forum of international experts was established, representing acknowledged laboratories throughout the world. Aalborg University has contributed to all aspects of this work, with a particular focus, though, on our hearing at low frequencies. In this region, only few laboratories have produced data. There has especially been lack of data at high levels, a natural consequence of the technical problems in producing these sounds accurately and without distortion. The international research cooperation has run parallel to and has supported the standardization process, and there is now general agreement about new data and their foundation in models of loudness. Revised international standards have been issued (ISO 226:2003 and ISO 389-7:2005) This international cooperation was made possible due to generous economic support from NEDO (New Energy and industrial technology Development Organization, Japan). Partners were: Yoiti Suzuki, Tohoku University, Japan (research coordinator); Volker Mellert, Oldenburg University, Germany; Utz Richter, Physikalisch-Technische Bundesanstalt, Germany; Henrik Møller, Aalborg University, Denmark; Leif Nielsen, Danish Standards Association, Denmark; Rhona Hellman, Northeastern University, USA; Kaoru Ashihara, Electrotechnical Laboratory, Japan; Kenji Ozawa, Yamanashi University, Japan; Hisashi Takeshima, Sendai National College of Technology, Japan. Supported by STVF/FTP.