The Loudness Level of Random Noise
Walter A. MacNair · The Journal of the Acoustical Society of America · 1934
A calculation according to the method of Fletcher and Munson is made of the loudness level of noise of the random type such as “thermal agitation” noise. The comparison is made that noise of this type changes in loudness level 5 decibels for every 3 decibels change in intensity level if this level is between 0 and 40 decibels above threshold, the range in which noise is frequently heard; whereas the loudness level of speech changes about 3 decibels for every 3 decibels change in intensity level if this level is greater than 60 decibels above threshold, the range in which speech is usually heard.