GHM DeltaOHM HD2010UC, Operating Manual

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HD2010UC
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V4.2
In the figure, the equivalent level profile is highlighted. It is stabilizing within few minutes to
a level just above 71dBA.
Considering an intermittent source of noise (for example a train passing by), it is obvious that the
equivalent level can give a measurement of the mean energy level after considering many passages.
If you wish to measure the energy content of a single passage, you need to use a different
measurement parameter, the “Sound Exposure Level”, symbols SEL or L
E
(IEC 60804/IEC 61672).
The sound exposure level is defined as the constant sound level for 1 second that contains the same
energy of the event being examined. By standardizing the SEL value (1 second), it is possible to
compare sound events with different durations.
S
TATISTICAL
A
NALYSIS
If you need to examine, from a statistical viewpoint, the distribution in time of the sound pres-
sure level, you have to use the percentile levels. A percentile level, symbolized as L
x
is defined as
the sound level being exceeded by the X percentage during the total time. To calculate the percen-
tile levels you first need to classify the sampled sound level according to regular intervals (usually
1/8s) in width classes, usually between 0.1dB and 2dB. At the end of the acquisition the probability
for each class is calculated by dividing the sampling frequency by the total number of samples. The
result is the sound level distribution of probabilities shown below.