D-2 824 Reference Manual 11/3/00
(unsteady) sound levels. If the Measurement Duration is the
same as the Criterion Duration, then L
avg
=L
TWA(LC)
where the Measurement Duration (specified time period) is
T=T
2
-T
1
and q is the Exchange Rate Factor. Only sound lev-
els above the Threshold Level are included in the integral.
Standard
: ANSI S12.19
Community Noise Equivalent
Level (CNEL, L
den
)
A rating of community noise exposure to all sources of
sound that differentiates between daytime, evening and
nighttime noise exposure. The equation for it is
The continuous equivalent sound level is generally calcu-
lated on an hourly basis and is shown in the equation as L.
The levels for the hourly periods from midnight to 7 a.m.
have 10 added to them to represent less tolerance for noise
during sleeping hours. The same occurs from 10 p.m. to
midnight. The levels for the hourly periods between 7 p.m.
and 10 p.m. have 5 added to them to represent a lessened tol-
erance for noise during evening activities. They are energy
summed and converted to an average noise exposure rating.
Criterion Duration (T
c
)
It is the time required for a constant sound level equal to the
Criterion Level to produce a Noise Dose of 100%. Criterion
Duration is typically 8 hours.
Example
: If the Criterion Level = 90 dB and the Criterion
Duration is 8 hours, then a sound level of 90 dB for 8 hours,
will produce a 100% Noise Dose. See Noise Dose.
Standard
:
ANSI S12.19
Criterion Sound Exposure
(CSE)
The product of the Criterion Duration and the mean square
sound pressure associated with the Criterion Sound Level
when adjusted for the Exchange Rate. It is expressed in Pas-
cals-squared seconds when the exchange rate is 3 dB.
L
avg
qLog
10
1
T
---
10
L
p
t
()()
q
⁄
T
1
T
2
∫
dt
=
L
den
10log
10
10
L
i
10+
()
10
⁄
0000
0700
∑
10
L
i
10
⁄
0700
1900
∑
10
L
i
5+
()
10
⁄
1900
2200
∑
10
L
i
10+
()
10
⁄
2200
2400
∑
++ +=
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