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Appendix E

Glossary

A-weighting Filter: Frequency weighting corresponding approximately to the 40 dB equal

loudness curve, that is to say, the human ear’s response at low to medium

sound levels. It is by far the most commonly applied frequency weighting

and is used for all levels of sound.

B-weighting Filter: Frequency weighting corresponding approximately to the 70 dB equal

loudness curve, that is to say, the human ear’s response at medium sound

levels.

C-weighting Filter: Frequency weighting corresponding to the 100 dB equal loudness curve, that

is to say, the human ear’s response at fairly high sound levels. Mainly used

when assessing peak values of high sound pressure levels.

Criterion Level: Criterion Level is the maximum averaged sound level allowed for an 8-hour

period. Used for calculation of Dose, ProjDose, DoseUQ and ProjDoseUQ,

where U = F or S and Q = 4, 5 or 6 dB.

Decibel (dB): The measurement unit for expressing the relative intensity of sound. A direct

application of linear scales (in Pa) to the measurement of sound pressure

leads to large and unwieldy numbers. As the ear responds logarithmically

rather than linearly to stimuli, it is more practical to express acoustic

parameters as a logarithmic ratio of the measured value to a reference value.

This logarithmic ratio is called a decibel or dB. The advantage of using dB

can be clearly seen in the below illustration. Here, the linear scale with its

large numbers is converted into a manageable scale from 0 dB at the

threshold of hearing (20 Pa) to 130 dB at the threshold of pain (100 Pa).

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