我們常用分貝來描述聲音的強度

dB (分貝) is defined as,

db = 10.log(I/Io)
where I is the sound intensity
Io is the threshold of hearing

hence, 80 db = 10.log(I/Io) where I is the sound intensity at 80 dB
I = Io.10^8

20 db = 10.log(I'/Io) where I' is the sound intensity at 20 dB
I' = Io.10^2

Therefore, I/I' = 10^8/10^2 = 10^6 (i.e. 1 million times 一百萬倍)