10 Sound and the Ear /I : 2 



TABLE I 

 Various Sound Pressure Levels 



Dynes/cm 2 SPL 



160 db 

 10,000.00 Mechanical damage to human eardrum 



100.00 



0.01 



140 Pain threshold 

 Jet motor 



120 Discomfort threshold 



Riveter (peak values) 



Damage to human hearing after prolonged exposure 

 100 Average factory 

 Subway car 

 Automobile 



80 Class lecture 

 1.00 Loud radio 



60 Typical office 



Conversational speech 



40 Average living room 



20 Very quiet room 



0.0002 Threshold of hearing 



In air it is customary to use forp the arbitrary value 2 x 1 " 4 dynes/cm 2 . 

 The 20 in the definition of decibels (db) arose out of historical reasons; 

 from the properties of logarithms, one might equally well write this as 



