Sound pressure level is indicated by notation SPL, Its definition as the ratio of Sound pressure effective valuep(e) and Reference sound pressurep(ref) to be measured is use logarithms and multiplied by 20, that is,

.

SPL=20LOG(10)[p(e)/p(ref)]

Its unit is decibels (dB).

The Reference sound pressurep(ref) in the air is generally taken as 2*10E-5 pa, and this number value is the sound pressure value that the normal ear can just detect for 1 KHZ sound, that is, the audible threshold sound pressure of 1 KHZ sound. Generally speaking, below this sound pressure value, the human ear can no longer detect the existence of the sound. Obviously, the audible threshold Sound pressure level is zero decibels.

Sound pressure level(SPL)：

Sound pressure level(SPL)：
SPL ＝ 20log₁₀(P/P_ref)

SPL = Sound pressure level(SPL)

P = Sound pressure effective value

P_ref = Reference sound pressure