188 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 3 2 



Among the loudest things one is likely to encounter are the noises 

 of riveting, pneumatic road drilling, steamship sirens, and printing 

 presses. More untoward events are lions and Niagara Falls, which 

 can apparently roar equally loudly (85 decibels). 



But the arch offender of all is the airplane engine at close quarters 

 (110 decibels). The noise in the cabins of airplanes in flight ranges 

 between 80 and 110 decibels, according to the type of machine. The 

 noise of the propeller is probably the dominant factor, though engine 

 exhaust and general engine clatter run it close, and all three must 

 be seen to if an improvement is to be apparent. There are, however, 

 good prospects that the noise in airplane cabins will presently be 

 substantially reduced (possibly to that of a railway train) by using 

 propellers with lower tip speeds, providing more effective silencers 

 on the exhausts, reducing engine clatter by inclosing the engines, and 

 constructing cabins of double walls containing a suitable filler. In 

 this connection, see Davis (Journ. Roy. Aer, Soc, 1931). 



PROTECTION FROM NOISE 



The best way of securing protection from noise is to quiet it at its 

 source. This is much more effective than trying to control it later. 

 For example, machines may be enclosed or better balanced, or better 

 shaped, and mounted on insulating materials. 



As regards traffic noise, a great deal of the more objectionable 

 noise is due to vehicles which are ill-cared for and in bad condition 

 or badly loaded. Indiscriminate horn-blowing is not, I think, a 

 characteristic British trait. 



Where there is considerable traffic noise, much can be done to add 

 to the comfort of a building by creating sound shadows, and by archi- 

 tectural ingenuity in providing " buffer " rooms, a recent example of 

 which is afforded by the new Headquarters of the British Broadcast- 

 ing Corporation. 



The protective shielding by buildings is well illustrated by the 

 sylvan quietness of inclosed quadrangles, such as the Inns of Courts, 

 which are in close proximity to noisy streets. The bedrooms opening 

 on an hotel courtyard are usually much quieter than a room on the 

 outside of the building, though sometimes the domestic quarters are 

 so situated as to nullify the advantage. 



NOISE-PROOFING WALLS 



There are two main practical methods for insulating an inclosure 

 against air-borne noises: 



(a) By using single nonporous rigid walls or partitions. 



(h) By using multiple partitions as independent as possible and 

 separated by air or some kind of loose filling. 



