Hearing Thresholds and Equal Loudness Contours in Free Field at Frequencies below 1 kHz

Abstract

Hearing thresholds for pure sinusoidal tones were determined in a free field at frequencies from 25 Hz to 1 kHz. Contours of equal loudness were determined at the same frequencies at loudness levels from 20 phon to 80 phon in steps of 20 phon. 12 subjects participated. The psychometric method used for the threshold determinations was the method of limits. The deviations from minimum audible field values given in ISO/R226 were small (3 dB at most frequencies). For the measurement of equal loudness the reference was a 1 kHz tone, and other tones were compared to that. The psychometric method was the method of limits. The resulting equal loundess contours were positioned at much higher levels than those of ISO/R226. Similar results have recently been reported by others. At low loudness levels the results were in good agreement with the curves obtained by Fletcher and Munson, but at high loudness levels they were also above their curves. Some of the points of equal loudness were also determined by a maximum likelihood estimation method. The results differed slightly from those obtained by the method of limits.