Larson Davis 831, User Manual

Page: 515 / 548

C-2 Basic Integrated Level Calculations Model 831 Manual
Note that the format used by the 831
to display equivalent continuous
sound pressure level is
L
Xeq
, where
X is the frequency weighting ( X = A,
C or Z ).
When a frequency weighting other than A is used, the
frequency weighting used shall be included explicitly in the
title and the formula of the quantity, for example equivalent
continuous C-weighted sound pressure level:
If no frequency weighting is used, the quantity is simply
called equivalent continuous sound pressure level.
Time-Weighted Averages
The Larson Davis 831 calculates many time-integrated
levels or time-weighted averages (TWA) based on different
parameters and time intervals. They are all designed and
programmed to perform the equation specified in IEC
61672-1 with allowances for the following:
A, C and Z frequency weighting characteristics
Various interval times, both fixed interval TWAs and
variable interval event TWAs
Exchange-rates, or “doubling rates” can be entered that
effect certain TWA measurements
Certain TWA measurements include a programmable
threshold with only levels above this threshold contributing
to the measurement
No attempt is made to meet the IEC 61672-1 requirement to
title the TWA by frequency weighting and time interval
within the analyzer’s display or report system. The
Frequency Weighting and Time Interval are both displayed
in the same view to meet this requirement.
The following figure indicates how the requirements are met
in the 831.
 
 
dB P d P
T
L L
T t
C














 


0
2 / 1
2
CeqT CT
/
1
lg 20

 