Brüel & Kjær 2240 Guide De L'utilisateur page 42

36 Integrating-averaging Sound Level Meter Type 2240 – User Guide
A-weighting filter:
C-weighting filter:
decibel (dB):
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. See also C-
weighting and frequency weighting.
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. See also A-
weighting and frequency weighting.
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 μPa) to 130 dB
at the threshold of pain (∼100 Pa).