The sound pressure perception of the human auditory system extends over 14 powers of ten between the hearing threshold and the pain threshold. These enormous differences in sound pressure are best handled in logarithmic representation, and are therefore expressed in decibels( dB).
For Sound Pressure Level( SPL), the sound pressure levels are related to the reference level at the hearing threshold, which is '10^-12 W/m^2'. The formula for Decibel Sound Pressure Level (dBSPL) is `10*log10^-12`, with "X" as sound pressure in watts per square meter.
Sound perception is manifested in hearing characteristics and shows a strong frequency dependence. For this reason, the frequency weighting of the sound pressure is done with different filters. One of the most well-known and in the technology used evaluation procedures reproduces in filters the human hearing characteristic. The measured dB value is given in dB(A). As further evaluation characteristics there are the evaluation functions dB(B), dB(C) and dB(Z).