Loudness is evaluated in the workplace regulation with different filters. For sound pressure measurements, there are the filter curves according to A-Weighting, B-Weighting and C-Weighting. In addition, there is the flat frequency response curve according to Z-Weighting.
While A-Weighting uses a filter characteristic corresponding to a volume of 40 phon and B-Weighting works for higher volumes at 70 phon, C-Weighting is used for peak sound pressures with a reference characteristic of 90 phon. With this filter characteristic, the deviations at high and low tones are much less pronounced than with the other two measurement curves. Sound level meters for dB(C) weighting measure "dB above Reference Noise with C-Weighting", dBrnC.