Pn,(△Pn) Intensity I: 1=av (19-19) The response of the ear to sound of increasing intensity is approximately logarithmic. One can define a logarithmic scale of intensity called the sound level sl SL=10 log (1920) Where I is a reference intensity which is chosen to be 10 -12w/m2(a typical value for the threshold of human hearing〔听觉阈)Intensity I: (19-19) The response of the ear to sound of increasing intensity is approximately logarithmic. One can define a logarithmic scale of intensity called the “sound level SL” (19-20) Where is a reference intensity, which is chosen to be (a typical value for the threshold of human hearing(听觉阈)). 0 10log I I SL = 0 I 12 2 10 w/ m − v P A P I av m 2 ( ) 2  = =