Crystal Instruments Spider - SLM Measures

Spider DSA User’s Manual
241
equivalent to an exponential averaging mode to calculate LAF; the second path
goes to a time averaging function, which is equivalent to a linear averaging mode
to calculate Leq.
With A-weighting applied as shown in the example, the list of symbols used by the
instrument is:
Symbol of
Measured
Values
Description
LAF
A-weighted, F time-weighted sound level
LAFmax
Maximum A-weighted, F time-weighted sound level
LAFmin
Minimum A-weighted, F time-weighted sound level
LCpeak
Peak C sound level, greatest absolute instantaneous
C-weighted sound pressure level
Lpeak
Peak sound level, greatest absolute instantaneous
sound pressure level
LAeq
A-weighted, time-average sound level (equivalent
continuous sound level)
LAeqmax
Maximum A-weighted, time-average sound level
(equivalent continuous sound level)
LAeqmin
Minimum A-weighted, time-average sound level
(equivalent continuous sound level)
LAE
A-weighted sound exposure level
LN (N = any
integer
between
0~100)
Statistical Level general term
L1, L5, L50,
L95....
Statistical Levels with specific N values. The sound
level exceeds this level 1, 5, 50 or 95 percent of the
time for the duration of the measurement.
SLM Measures
There are two ways to view sound level measurements: instantaneous SLM
measurement and RMS history. Instantaneous SLM measurements represent the
most current value of the subject variable.
RMS history not only shows the most current value, but also a record of historical
values against time or RPM. Some of the measures allow only instantaneous
values others allow both.
The following SLM measurement are available for real-time reading and can be
saved as a data structure for future review.
Time Weighted Sound Levels
Time weighted sound level is the output of frequency-weighting and then time
weighting filters. Time weighting serves an exponential averaging operator. The
computation is illustrated in Figure 150.