MEASUEEMENT OF NOISE KAYE 



183 



about 20 feet away illustrates a loudness of about 80 decibels. Twins 

 crying together are only 3 decibels louder than one crying alone. 

 Another way of increasing a noise by 3 decibels is for the observer to 

 move 30 per cent nearer (that is, when in the open air). Another 

 20 per cent (that is, halving the distance) and the total gain will 

 be 6 decibels. 



Loudness Levels o{ Common Noises 



Decibels (ibove 

 Threshold 



In Pile aeroplane ^ 

 (vcrij noisij) 



in t'he t'rain 

 (noisu) 



In Hie sPreel* 

 (aweracjc) 



In Hhe home 

 (auieV) 



In Vhe counPrij ^ 

 (veru auiel') 



40 

 30 

 20 







Noisii aepoplcine cabin 

 Pneumal'ic road drill 

 In Piibc frain (London) 

 Vcri] biisij fro^^ic (London) 

 In sPccim t'rain (w^indow opciO 

 Ordinciri] coiiversahon (S^l") 

 In t^uieP saloon car (30m. ph.) 

 Suburban sPreel* 

 Quiel* c^avden (suburbs^ 

 Quiel' whisper (S^O 

 Threshold o{ hearina 



FlGUEE 8 



Figure 8 shows a kind of " noise thermometer " of common noises 

 ranging up to 100 decibels — a level which is unlikely to be exceeded 

 in everyday experience. Some broad general groupings of noises 

 are indicated on the left. Above 50 decibels the scale is differenti- 

 ated as containing in general those noises which we should do well to 

 endeavor to moderate as far as it may be practicable to do so, and 

 we can perhaps regard this figure as a kind of " temperate " level 

 on our noise thermometer. 



