C-2
Model 820 Technical Reference Manual
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 levels above the
Threshold Level are included in the integral.
Standard
: ANSI S12.19
Calibration
Adjustment of a sound or vibration measurement system so that it
agrees with a reference sound or vibration source. It should be
done before each set of measurements.
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 calculated 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 repre-
sent a lessened tolerance for noise during evening activities. They
are energy summed and converted to an average noise exposure
rating.
L
avg
qLog
10
1
T
--- 10
L
p
t
( )
(
)
q
⁄
T
1
T
2
∫
dt
⎝
⎠
⎜
⎟
⎜
⎟
⎛
⎞
=
Lden
10log10
10
Li
10
+
(
)
10
⁄
0000
0700
∑
10
Li
10
⁄
0700
1900
∑
10
Li
5
+
(
)
10
⁄
1900
2200
∑
10
Li
10
+
(
)
10
⁄
2200
2400
∑
+
+
+
=