Larson Davis 831, User Manual

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Model 831 Manual Glossary D-7
Department of Defense Level
(L
DOD
)
The Average Sound Level calculated in accordance with
Department of Defense Exchange Rate and Threshold Level.
See Average Sound Level
Dose
(See Noise Dose)
Detector
The part of a sound level meter that converts the actual
fluctuating sound or vibration signal from the microphone to
one that indicates its amplitude. It first squares the signal,
then averages it in accordance with the time-weighting
characteristic, and then takes the square root. This results in
an amplitude described as rms (root-mean-square).
Eight Hour Time-Weighted
Average Sound Level (L
TWA(8)
)
It is the constant sound level that would expose a person to
the same Noise Dose as the actual (unsteady) sound levels.
The equation for it is
NOTE: This definition applies only for a Criterion Duration
of 8 hours.
Standard : ANSI S12.19
Energy Equivalent Sound Level
(L
eq
)
The level of a constant sound over a specific time period that
has the same sound energy as the actual (unsteady) sound
over the same period.
where p is the sound pressure and the Measurement
Duration (specific time period) T=T
2
-T
1
. See Sound
Exposure Level.
Exchange Rate (Q), Exchange
Rate Factor (q), Exposure
Factor (k)
It is defined in ANSI S1.25 as “the change in sound level
corresponding to a doubling or halving of the duration of a
sound level while a constant percentage of criterion
exposure is maintained.” The rate and the factors are given
L
TWA 8
 
L
c
qLog
10
D
100
---------
 
 
+ =
L
eq
10 Log
10
p
2
t
 
t d
T
1
T
2

p
o
2
T
--------------------------
=