Equal-loudness-level contours provide the foundation for theoretical and practical analyses of intensity-frequency characteristics of auditory systems. Since 1956 equal-loudness-level contours based on the free-field measurements of Robinson and Dadson [Br. J. Appl. Phys. 7, 166-181 (1956)] have been widely accepted. However, in 1987 some questions about the general applicability of these contours were published [H. Fastl and E. Zwicker, Fortschritte der Akustik, DAGA '87, pp. 189-193 (1987)]. As a result, a new international effort to measure equal-loudness-level contours was undertaken. The present paper brings together the results of 12 studies starting in the mid-1980s to arrive at a new set of contours. The new contours estimated in this study are compared with four sets of classic contours taken from the available literature. The contours described by Fletcher and Munson [J. Acoust. Soc. Am. 5, 82-108 (1933)] exhibit some overall similarity to our proposed estimated contours in the mid-frequency range up to 60 phons. The contours described by Robinson and Dadson exhibit clear differences from the new contours. These differences are most pronounced below 500 Hz and the discrepancy is often as large as 14 dB.

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IntroductionAn equal-loudness level contour (ELC) is defined as a curve that ties up the sound pressure levels having equal loudness as a function of frequency. ELCs over the whole range of audibility have been standardized as ISO 226 [1], which is based on the data provided by Robinson and Dadson [2]. In 1985, Fastl and Zwicker [3] reported that equalloudness levels of 70 phons at around 400 Hz specified in ISO 226 were inconsistent with those estimated by Zwicker's loudness calculation method specified in ISO 532B [4]. This report triggered works to re-determine the ELCs. The authors have been conducting a series of experiments to obtain ELCs for Japanese subjects [5][6][7][8]. Similar experiments have been conducted in Germany and in Denmark [9][10][11][12][13]. All these recent studies have consistently shown that equal-loudness levels at frequencies below 1 kHz are significantly higher than the corresponding contours specified in ISO 226.In the high frequency range, however, only few sets of data are available above 70 phons in recent data [5][6][7][8][9][10][11][12][13]. Equal-loudness levels of 90 phons were measured at frequency up to 4 kHz [8] and those of 80 phons were measured up to only 1 kHz [11,13]. Therefore, if new equalloudness contours were standardized based on such recent data, it would be quite difficult to standardize the new contours above 70 phons at frequencies above 1 kHz because of the lack of data above 1 kHz at 80 phons. Hence, equalloudness levels at 80 phons for frequencies from 1 kHz to 12.5 kHz as well as equal-loudness levels at 60 phons and thresholds of hearing for the same frequency range were measured in this study. Equal-loudness levels at 60 phons were measured because only one research group, Betke and Mellert [9], has reported data above 1 kHz.