The hearing and loudness perception of humans is determined by the psychoacoustic hearing perception, which is expressed in the hearing characteristics. In order to be able to evaluate the sound pressure perceived by the human auditory system, the auditory perception is therefore simulated when measuring the sound pressure at workplaces.
For this purpose, sound level meters are preceded by filters that simulate the anatomical characteristics of the human auditory system and the hearing characteristics. This sound pressure evaluation whose filter characteristics are based on a frequency weighting curve with a volume of 40 phon is marked with the letter (A). At high and low frequencies, higher sound pressures are required for the same loudness perception than at the average frequency of 1 kHz.TCO 95, the limit value may not exceed 38 dB(A) when a personalcomputer is in operation, and 32 dB(A) when it is idle.