The Computation of the Composite Noise Resulting 

 from Random Variable Sources 



By E. DIETZE and W. D. GOODALE, Jr. 



A statistical method is described for computing the meter read- 

 ing which would be obtained on a sound level meter when used to 

 measure room noise resulting from the random concurrent opera- 

 tion of a number of intermittent or continuous noise sources. 

 The application of the method in the solution of practical problems 

 is illustrated. 



IT 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,^ etc. 



It has also been recognized that the ear itself, in general, is not a 

 convenient means for the accurate measurement of loudness, espe- 

 cially in absolute terms. To overcome this difficulty sound level 

 meters ^ 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 out- 

 puts are random, discontinuous variables. The paper does not con- 

 cern 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 recog- 

 nized, of course, that not only are sound level meter readings an in- 

 complete description of the effect of a change in noise but that con- 

 siderable experience is required to appreciate properly the significance 

 of the decibel unit employed. 



Types 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. To illustrate, consideration may be given to reducing 

 1 For reference see Bibliography. 



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