Studying equal loudness level contours with Rhona Hellman

Dr. Rhona Hellman stayed at Tohoku University as a Visiting Associate Professor once for a half year during March-September 1997, and then for three months in 1998. She completed her PhD dissertation, "Growth of Loudness for Individuals and Groups in Normal and Cochlear-impaired Hearing," at Tohoku University during these stays [1]. At that time, we were investigating the equal-loudness-level contours for pure tones for revision of the international standard (ISO 226). To give the loudness-level contours in conformance with experimental data obtained at specific frequencies and loudness levels, some interpolation is necessary. Ill-shaped curves might result if a contour for a certain loudness level is depicted independently of other contours. To avoid this inexpedience, the use of knowledge of the loudness growth function is extremely helpful. In completing our work for the present ISO 226:2003, the loudness growth function proposed by Zwislocki and Hellman in 1960 was used, with great benefit. Moreover, we jointly conducted psychoacoustical measurements of loudness growth to determine equal loudness levels at high frequencies. This presentation describes our experience with Dr. Rhona Hellman while investigating these topics.