1. 1) ISO 226, Acoustics – Normal Equal-Loudness-Level Contours (International Organization for Standardization, Geneva, 2003).
2. 2) ISO 389-7, Acoustics – Reference Zero for the Calibration of Audiometric Equipment – Part 7: Reference Threshold of Hearing under Free-Field and Diffuse-Field Listening Conditions (International Organization for Standardization, Geneva, 2005).
3. 3) ISO 28961, Acoustics – Statistical Distribution of Hearing Thresholds of Otologically Normal Persons in the Age Range from 18 Years to 25 Years under Free-Field Listening Conditions (International Organization for Standardization, Geneva, 2012).
4. 4) K. Kurakata, T. Mizunami, K. Matsushita and K. Ashihara, ``Statistical distribution of normal hearing thresholds under free-field listening conditions,'' Acoust. Sci. & Tech., 26, 440-446 (2005).
5. 5) K. Kurakata, T. Mizunami and K. Matsushita, ``Percentiles of normal hearing-threshold distribution under free-field listening conditions in numerical form,'' Acoust. Sci. & Tech., 26, 447-449 (2005).