May 2015 Page 39 of 51
15. Glossary of Terms
A-Weighting is the standard weighting of the audible frequencies designed to
approximate the response of the human ear to noise.
Acoustic Calibrator is an instrument that provides a reference noise source with a
standard level and frequency. This is used to calibrate and check the
performance of sound level meters and noise dosimeters.
ANSI S1.25 - 1991 is the U.S. Standard for Noise Dosimeters.
C-Weighting is the frequency response of the human ear which varies with the
sound intensity. At high noise levels typically greater than 100 dB,
the ear’s frequency response becomes flatter and is represented by
the C weighting filter shape.
C weighting is primarily used for Peak measurements (LCPk) or for C
weighted equivalent Level (LCeq).
Criterion Level (CL) is the normalised eight hour average weighted sound level in dB that
corresponds to the maximum permitted daily exposure or 100% noise
dose.
Criterion Time (CT) is the time, in hours, used in the calculation of the %Dose.
dB(A) is the A-weighted sound level in decibels.
dB(C) is the C-weighted sound level in decibels
dB(Z) is the Z-weighted sound level in decibels
Decibel (dB) is the standard physical unit for measuring sound level and noise
exposure.
Estimated Exposure is a calculated estimate of the exposure of the wearer if the average
level measured continues for the period defined by the Criterion Time.
Estimated exposure is expressed in Pascal Squared Hours (Pa
2
h).
Fast Time Weighting is a standard time weighting applied by the sound level measurement
instrument.
IEC 61252 is the International Standard for Personal Sound Exposure Meters.
LAE is the A-weighted exposure level. It is the level that would contain the
same amount of energy in one second as the actual noise has during
the whole measurement period.
LAeq is the A-weighted equivalent level, i.e. the A-Weighted average noise
level over the measurement period. According to ISO procedures, a
doubling in energy results in a 3dB change in the Leq or an ‘exchange
rate’ of Q=3. There is no Threshold value taken into account.
LAF is the A-weighted sound level measured with Fast Time Weighting.
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