186 ANNUAL REPORT SMITHSONIAN INSTITUTION, 193 2 



Table 1. — Loudness levels of various noises — Continued 

 TRAIN NOISES— Continued 



In American Pullman railway car (Parkinson): 



3 decibels increase in noise for 10 miles per hour increase in speed. 

 5 decibels increase in noise by opening window. 



5 decibels Increase in noise when passing another train. 

 10 decibels increase in noise in tunnel. 



6 decibels increase in noise in corridor. 



5-10 decibels decrease in noise when berths are made up. 



References: 



Davis, Journal Royal Aeronautical Society, 1931. 

 Free, Journal Acoustical Society of America, 1930. 

 Gait, Journal Acoustical Society of America, 1930. 

 Parkinson, Journal Acoustical Society of America, 1930. 



Figure 9 (due to Gait, Journ. Acoust. Soc. Amer., 1929) shows 

 masking measurements of crowd noises obtained by the use of a 

 3-band warbler audiometer on the occasion of Lindbergh's arrival in 

 New York after his Atlantic flight. The observers were on the fifth 

 floor, about 110 feet from the street. The masking effects of the 

 noise produced by the crowd's welcome as Lindbergh passed are 

 pronounced — quite sufficient, in fact, to mask the sound of a brass band 

 not many yards distant. It is clear that here is a quantitative 

 method, as Mr. Gait remarks, by which footlight and other favorites 

 of the public can periodically assess their popularity ! 



As regards the individual components of traffic noise, it would 

 seem from the limited data available that British and American 

 tramcars do not on the average differ appreciably as regards noise. 

 The same remark probably holds for motor cars. It is of interest to 

 note quantitative evidence that a modern car at moderate speed is 

 quieter than a horse vehicle on a paved street. 



Among the contributory factors to traffic noise are motor horns, 

 into the noisiness and stridency of which an inquiry of a restricted 

 character was undertaken in 1929 by the National Physical Labora- 

 toiy on behalf of the Ministry of Transport. Observations were 

 made in a closed chamber with heavily lagged walls. Both physical 

 and aural methods of measuring noise were employed, cathode-ray 

 oscillograph records being also made of the average wave form. It 

 appeared from the limited observations that stridency was bound up 

 largely with sheer loudness, but that strong high-frequency com- 

 ponents, strong unrelated notes, and any marked starting character- 



