Loudness adaptation may be measured by a simultaneous loudness balance, or, as in the two experiments reported below, by a median plane localization of a dichotically presented acoustic stimulus. The loudness of a steady auditory stimulus generally decreases with time. That is, the intensity of a comparison stimulus in the rested ear is ordinarily set below the intensity in the stimulated ear.
Two experiments were done on loudness adaptation for bands of noise. In Experiment 1, using 36 subjects, loudness adaptation for a wide‐band thermal noise of 100–5000 cps was studied as a function of five SPL's: 40, 70, 90, 100, and 105 db over all. The mean maximum loudness adaptation obtained was 2.3, 9.9, 11.4, 14.4, and 16.3 db, respectively. The mean standard deviation for all measures was 6.1 db, and the distributions of the sets of measures tended to be skewed toward greater adaptation.
In Experiment 2 (12 subjects), the loudness adaptation for a 1500‐cps tone was compared with that for bands of noise whose centers (mel scale) were at 1500 cps, and whose over‐all SPL's were equal to the SPL of the pure tone. The band limits in cycles per second were 1280–1120, 1075–1950, 720–2600, and 100–4900. For each band, adaptation was measured for 50, 70, and 90 db SPL over all. The essential results are: (1) Loudness adaptation for 1500 cps is about 8.5 db greater than the maximum adaptation for any noise band at any SPL; (2) Adaptation is small (4.5 db) at 50 db for all bands of noise; it is complete within one minute and is about equal for all band widths; (3) At 70 and 90 db, time taken for complete adaptation increases and the two widest bands give greater adaptation than the two narrowest bands. At 90 db a trend becomes clear: the wider the band, the greater the degree of adaptation and the longer the time required for maximum adaptation to be attained.