654 BELLS YS TE M TE CHNI CA L JO UR NA L 



Otherwise. The second series of tests was made for the purpose of de- 

 termining the difference between the room noise encountered under 

 winter conditions and that encountered under summer conditions. 

 Consequently, a selected group of the locations, which had been meas- 

 ured in the winter, were measured again under summer conditions. 



It must be appreciated, in generalizing from the data given, that 

 tests were made in only a limited number of locations. 



Two methods were employed in making the measurements described 

 in this paper, one electrical and the other aural. The electrical method 

 employed a condenser-transmitter pick-up, amplifiers, and detector. 

 A weighting network was incorporated in the amplifier to simulate the 

 sensitivity characteristic of the ear. The aural method, known as the 

 "masking method," involved the measurement of the masking effect of 

 the noise on various warbler tones recorded on a phonograph record. 

 Both of these methods will be described in greater detail below. 



General Results 



Some of the interesting results which were obtained from this survey 

 may be summarized as follows: 



On the average, room noise in residences was about 20 db less in mag- 

 nitude than that in business locations. 



The spread in the magnitudes of business room noises was about 

 40 db, as compared to 20 db for residence room noises. These spreads 

 include 90 per cent of the measurements, excluding the lowest and high- 

 est 5 per cent. The standard deviation of the measurements was about 

 12 db for business noise and 6 db for residence noise. 



Room noises averaged 4 or 5 db higher in summer than in winter. 



In general, the magnitude of residence noise was affected to only a 

 minor extent by the size of the town or city in which it was measured. 



On the average, the frequency composition of residence noise was 

 about the same as that of business noise. The masking effect of the 

 noise on a tone covering the range 750-1500 cycles was greater than 

 that on ranges above and below this. The magnitudes of components 

 in the lower part of the range covered (about 250-5000 cycles) appeared 

 to be somewhat larger than those in the higher part of this range. 



Methods of Measurement 



The two methods which were employed in the survey are as follows : 



Aural Method — Masking of Warbler Tone.^ — In this method a tone 



of varying pitch (warble) is produced and sent into a receiver. The 



receiver cap is provided with slots shaped so that the observer's ear 



* R. H. Gait, Jl. Acoustical Soc. Ainer., October 1929, p. 147. 



