Larson Davis System 824, Technical Reference Manual

Page: 598 / 673

D-2 824 Reference Manual 9/29/09
Average Sound Level (L
avg
)
It is the logarithmic average of the sound during a
Measurement Duration (specific time period), using the
chosen Exchange Rate Factor. Exposure to this sound level
over the period would result in the same noise dose and the
actual (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
levels 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
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
L
avg
qLog
10
1
T
--- 10
L
p
t
( ) ( )
q
⁄
T
1
T
2
∫
dt
⎝ ⎠
⎜ ⎟
⎜ ⎟
⎛ ⎞
=
Lden 10log10
1
24
------
10
Li 10 +
( )
10
⁄
0000
0700
∑
10
Li 10
⁄
0700
1900
∑
10
Li 5 +
( )
10
⁄
1900
2200
∑
10
Li 10 +
( )
10
⁄
2200
2400
∑
+ + +
⎩ ⎭
⎨ ⎬
⎧ ⎫
=