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Ambient Noise
Commonly used for environmental noise purposes, this is the sound pressure
level in dB that is due to the ambient noise.
Generally it is the noise that exists under normal conditions at any given time
and can be with or without specific noise sources included. For the purposes of
the standard BS 4142 ambient noise is the totally encompassing sound
including all noise sources. See also ‘Residual Noise’.
Audio Frequency Range
This is the frequency range over which a normal human ear can detect sound.
The normal sound range usually decays with age and is approximately 20Hz to
20kHz.
Frequencies below 20Hz are known as infra sound and frequencies above
20kHz are known as ultra sound.
Audiometer
An electronic instrument that is used to apply known sound pressure levels to a
subject’s ear. These will be at various frequencies and levels and monitored one
ear at a time in order to determine a person’s hearing threshold.
It is intended to be used in an area with a very low ambient noise level such as
an audiometric booth and all tests should be conducted in accordance with the
standard BS EN ISO 8253-1.
Castle Group Ltd offers a range of audiometers and audiometric booths which
can be found at www.castlegroup.co.uk
Background Noise
This is the unwanted part of a measurement for a measured signal which is
caused by noise. For the purposes of the standard BS 4142 it is usually
measured as L90. See also ‘Ambient Noise’, ‘Residual Noise’ and ‘Percentile
Sound Levels’.
C-weighting
See ‘Frequency Weighted Filter’.
