The Computation of the Composite Noise Resulting from Random Variable Sources

TT is generally recognized that the effects of noise upon the individual exposed to it are, to a large extent, dependent on the loudness of the noise. Various tests have been made of the relation between loudness and the different effects of noise, such as interference with hearing, reaction on the nervous system, disturbance of rest, reduction of working efficiency,1 etc. It has also been recognized that the ear itself, in general, is not a convenient means for the accurate measurement of loudness, especially in absolute terms. To overcome this difficulty sound level meters 2 have been made available for the measurement of acoustic noises or sound in general. This paper is concerned with the application of such sound level meters in the study of noise problems and, in particular, with the question of determining the contribution of individual noise sources to the general "composite noise" including noise sources whose outputs are random, discontinuous variables. The paper does not concern itself with the attributes of loudness or the effects of noise, but merely with the computation of a meter reading of the total noise from available measurements of the noise components. It is recognized, of course, that not only are sound level meter readings an incomplete description of the effect of a change in noise but that considerable experience is required to appreciate properly the significance of the decibel unit employed. T Y P E S OF PROBLEM The method described in this paper has been developed to meet a very practical need experienced in the solution of a large variety of noise problems.