Environmental Engineering Reference
In-Depth Information
One-half octave band==
()
f
2
f
(2.8)
2
1
where
f
2
= 1/2 octave band
f
1
= Lower frequency band
One-thirdoctaveband==
()
f
3
2
f
(2.9)
2
1
where
f
2
= 1/3 octave band
f
1
= lower frequency band
Adding Noise Sources
When sound power is known:
ww
ww
+
+
1
2
L
w
=
10
log
(2.10)
0
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).
Sound Pressure Additions
When sound pressure is known:
2
p
p
SPL
(decibels) =10
log
(2.11)
2
0
where
p
2
/
p
2
= 10
SPL
/10
.
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
(2.12)
1
2
3
When adding any number of sources, whether or not the sources are identical, the
equation becomes
(
)
++
(
)
SPL
1
10
/
SPL
n
/
10
SPL
=
10
log
10
10
(2.13)
