Spider DSA User’s Manual
240
Figure 148shows the relationship between the Sound Exposure Level (SEL), the
Sound Pressure Level (SPL), and the Leq. The Leq is the constant level needed to
produce the same amount of energy as the actual varying sound (the SPL).
The SEL is the Leq normalized to 1 second. It is what the Leq would be if the event
occurred over a one second duration.
Statistical Level (L
N
)is defined as the sound pressure level which is exceeded
N% of the time over the duration of a measuring time interval. L0 is the
maximum level over the duration of the measurement. L100 is the minimum.
Data Processing Diagram
Figure 149 shows the data processing diagram for ONE input channel for all the
SLM measurements when A-weighting is applied.
Figure 149. Sound level meter computation diagram.
In the SLM measurement, after the digitized data comes in, it is split into three
paths: one goes to frequency weighting A, B, C or Z and one goes to C weighting or
no weighting. The peak detection is computed from the output of C weighting or
no weighting. The output of frequency weighting (A, B, C or Z) is further split into
two paths. The first will go to a time weighting function which is more or less
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