A Direct Comparison of the Loudness of Pure Tones

The loudness of pure tones of frequencies 60 to 4000 cycles and for intensities from the threshold to 90 T.U. above the 700 cycle threshold.---The loudness of eleven pure tones was studied by adjusting the voltage applied to a telephone receiver to make these tones as loud as certain fixed levels of a 700 cycle tone. The average results of 22 observers, 11 men and 11 women, were arranged as contour lines of equal loudness through the normal auditory sensation area in terms of r.m.s. pressure in ear canal as a function of frequency. Frequencies from 60 to 4000 cycles were used and intensities from threshold of audibility to 90 T.U. above the 700 cycle threshold. It was found that if the amplitudes of pure tones are increased in equal ratios the loudness of low frequency tones increases much more rapidly than that of high frequency tones. For frequencies above 700 cycles the rate is nearly uniform.A loudness unit.---As a loudness unit the least perceptible increment of loudness of a 1000 cycle tone was employed. In absolute magnitude this varies from level to level, but in the ordinary range of loudness it becomes constant. This unit takes into account the subjective character of loudness.Sources of variation in data on loudness.---The variability of the data from which the averages were computed was separated into a factor expressing dissimilarity of ears and another expressing errors of observers' judgment. There was no level at which the variances were a minimum. Dissimilarity of ears causes more variation than errors of observers' judgment. The variances showed no significant sex difference.