Loudness as a Function of Signal Duration
Arnold McC. Small, John F. Brandt, Philip G. Cox · The Journal of the Acoustical Society of America · 1962
Subjects were asked to change the level of a short noise burst in order to make it equally as loud as a standard 500-msec burst. Above some critical duration loudness is independent of duration but below it for each decade decrease in duration the level of the short burst must be increased about 12.5 db, independent of the level at which the standard burst is presented.