The sound pressure level is represented by the symbol SPL, which is defined as the ratio of the effective value of the sound pressure to be measured p(e) to the reference sound pressure p(ref) taken from the common logarithm and then multiplied by 20, that is:

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

Its unit is decibel (dB).

The reference sound pressure p(ref) in the air is generally taken as 2*10E-5 Pa. This value is the sound pressure value at which the normal human ear can just perceive the existence of a 1 kHz sound, that is, the audible threshold sound pressure of a 1 kHz sound. Generally speaking, below this sound pressure value, the human ear can no longer perceive the existence of this sound. Obviously, the sound pressure level of the audible threshold sound pressure is zero decibel.

Sound Pressure Level (SPL):

Sound Pressure Level (SPL):
SPL ＝ 20log₁₀(P/P_ref)

SPL = Sound Pressure Level (SPL)

P = effective sound pressure

P_ref = Reference sound pressure