噪音計算公式

The Sound Pressure Level:
Lp=10 log( p2 / pref2 )=10 log( p/pref )^2 = 20 log(p/pref )
where
Lp = sound pressure level (dB)
p = sound pressure (Pa)
pref = 2x 10-5 - reference sound pressure (Pa)

let sound pressure level : Lpm = sound pressure of machine,
, Lpb1 = sound pressure of background 1,
, Lpb2 = sound pressure of background 2,
sound pressure: pm - machine, pb1 - background 1, pb2 - background 2,

環境一:
Lpm-Lpb1=14 dB = 20 log (pm/pb1) (Equation 1)
Lpb1 = 66 = 20 log (pb1/pref)
pb1 = 39.9 x 10^-3 Pa

put into Eq.1,
14 = 20 log (pm / 0.0399)
pm ~ 200 x 10^-3 Pa

環境二:
Lpb2 = 50 = 20 log( pb2/pref )
pb2 = 6.3 x 10^-3 Pa

now, operate the machine in situation 2,
Lpm-Lpb2 = 20 log (pm/ pb2)
Lpm - Lpb2 = 30 dB

so, Lpm = 30 + 50 = 80 dB

機器在實驗室環境50分貝時,開機後是80分貝