Geoscience Reference
In-Depth Information
15.7.5.7
Adding Noise Sources When Sound Power Is Known
L
w
= 10 log (
w
1
+
w
2
)/(
w
0
+
w
0
)
where
L
w
= Sound power (watts).
w
1
= Sound power of noise source 1 (watts).
w
2
= Sound power of noise source 2 (watts).
w
0
= Reference sound power (reference 10
-12
) (watts).
15.7.5.8
Sound Pressure Additions When Sound Pressure Is Known
SPL
= 10 log
p
2
/
p
2
where
p
2
/
p
2
= 10
SPL
/10
.
SPL
= Sound pressure level (decibels).
p
= Measured root-mean-square (rms) sound pressure (N/m
2
, µba rs).
p
0
= Reference rms sound pressure (20 µPa, N/m
2
, µba rs).
For three sources, the equation becomes
(
)
+
(
)
+
(
/
)
SPL
/
10
SPL
/
10
SPL
10
SPL
=
10
log
10
10
10
1
2
3
When adding any number of sources, whether the sources are identical or not, the equation becomes
(
)
++
(
)
SPL
1
10
/
SPL
n
/
10
SPL
=
10
log
10
…
10
To determine the sound pressure level from multiple identical sources, use the following equation:
SPL
f
=
SPL
i
+ 10 log
n
where
SPL
f
= Total sound pressure level (dB).
SPL
i
= Individual sound pressure level (dB).
n
= Number of identical sources.
15.7.5.9
Noise Levels in a Free Field
SPL
=
L
w
- 20 log
r
- 0.5
where
SPL
= Sound pressure (reference 0.00002 N/m
2
).
L
w
= Sound power (reference 10
-12
watts).
r
= Distance (feet).
15.7.5.10
Noise Levels with Directional Characteristics
SPL =
L
w
- 20 log
r
- 0.5 + log
Q
where
SPL
= Sound pressure (reference 0.00002 N/m
2
).
L
w
= Sound power (reference 10
-12
watts).
r
= Distance (feet).
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