COMPUTATION OF THE COMPOSITE NOISE 619 



Applications 

 In the following, several applications of the theory are made to 

 illustrate its practical usefulness. 



I. The composite noise in a typing room is computed. This com- 

 puted noise is compared with actual measurements. The effect of 

 increased room absorption is discussed. 



II. The effect on the composite noise of installing additional office 

 equipment is computed for the two cases where this equipment pro- 

 duces a continuous noise and where its noise is intermittent. 



III. The maximum permissible noise from added equipment is de- 

 termined on the basis that the composite noise level shall not be 

 increased by more than 0.5 db. 



Problem I 



For the purpose of computing the noise at a given location in the 

 typing room, the following information was obtained : 



A distribution of the noise from a typical typewriter was measured 

 at a distance of 2 feet from the type bar guide while the machine 

 was being operated at a normal rate. This is shown by Curve A of 

 Fig. 1. 



A location was chosen as a point of observation, and the distances 

 between it and the typing desks were measured. 



Estimates of the time spent in typing at each desk were obtained 

 which, taken together with data on average typing speeds, gave infor- 

 mation on the number of typing peaks produced per minute at each 

 desk. 



Computation of the absorption of the room using the usual values 

 of absorbing coefficients ^ gave a value of 650 units for F. 



Noise due to other sources, such as conversation and street noise, 

 was negligible in this room. 



The table shown below was then prepared. 



In this table Column 2 gives the average noise A/ produced by 

 each of the sources at 2 feet distance. This value is the median point 

 of Curve A in Fig. 1. Column 3 is the average number of source peaks 

 per minute m, produced at each desk. Column 4 is obtained from 

 Column 3 by using Fig. 4. The total number of source peaks is 

 A'' = 750, and from Fig. 5 the composite noise weight factor w = 

 — 0.4 db. The distances between the observing position and each 

 source are given in Column 5 and the losses in db due to these distances 

 are given in Column 6. These values were obtained from Fig. 3 for a 

 value oi F — 650. Column 7 is obtained by subtracting the losses of 

 Columns 4 and 6 from the values of Column 2. 



