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decibel filter (dB(A))

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.

Filter Characteristics for Loudness Rating

Filter Characteristics for Loudness Rating

The dB(A) is a logarithmic value that has similar significance to the phon. Between the two quantities, 0 dB(A) is equal to 2 x 10exp-5 Pascal (Pa) sound pressure at 1 kHz. This value is also the hearing threshold.

dB(A)-evaluation of loudness

dB(A)-evaluation of loudness

The dB(A)-measurements and -values are defined in the Workplace Ordinance for the protection of workers against the immission of noise. There is a TA guideline from the VDI (Association of German Engineers ) from which the dB(A) values for industrial, commercial or residential areas for day and night are derived. For PC workplaces, the limit values are not only specified in the Workplace Ordinance, but also in the TCO guidelines. According to 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.

For evaluations of higher volumes, there are the filter curves (B) and (C) and the dB evaluations dB(B) and dB(C).

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Englisch: decibel filter - dB(A)
Updated at: 25.03.2011
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Translations: DE