TABLES 301-310A.— ACOUSTICS * 



309 



TABLE 301.— RELATIVE POWER AND FREQUENCY OF OCCURRENCE OF 

 VOWEL AND CONSONANT SOUNDS 100 



Vowels 



Initial and final consonants 



* Data selected and arranged by Cyril M. Harris, Bell Telephone Laboratories. 



ioo Fletcher, H., Speech and hearing, p. 74, D. VanNostrand, 1929. French, Carter, and Koenig, 



Bell System Techn. Journ., vol. 9, p. 290, 1930. 



TABLE 302.— SOUND LEVELS OF NOISE IN VARIOUS LOCATIONS 



It is customary to compare the pressure of all sounds in air with 0.0002 dynes/cm*. The 

 sound-pressure level of waves having a r.m.s. sound pressure of p dynes/cm 2 is defined as 

 20 log M (J/0.0002) decibels.t 



The following table gives some typical values of sound levels of noise in the locations 

 indicated : 



Sound 



level 



Location in db 



Electric power station, 



generating room 120 



Boiler factory 110 



Subway station, train passing 100 



Streetcar 85 



Factory 75 



Large store 65 



Sound 

 level 

 Location in db 



Average office 55 



Average residence with radio 50 



Average residence without radio... 43 



Quiet residence 35 



Radio broadcast studio 30 



Reference level, .0002 dynes/cm 1 . . . 



t The bel is a dimensionless unit for expressing the ratio of two values of power, the number of 

 bels being the logarithm to the base 10 of the power ratio. 



The decibel, abbreviated db, is one-tenth of a bel. When conditions are such that scalar ratios of 

 pressure amplitudes or particle velocities are the square roots of the corresponding power ratios, the 

 number of decibels by which the corresponding powers differ is expressed by 



20 log ifJP % ) db 

 where P t /p 2 represents the scalar ratio. This relationship is frequently applied where the scalar ratio 

 is not the square root of the corresponding power ratio, but such usage should be accompanied by a 

 specific statement of application. 



SMITHSONIAN PHYSICAL TABLES 



