Biology Reference
In-Depth Information
Sound intensity is related to the inverse square law, which states the amount of
reduction of a power source with the distance. In fact, in ideal conditions sound
power from a point source is spread over the surface area of a sphere where
P
ac
4
I
¼
π
r
2
where
r
is the distance from the source or the radius of the sphere.
Considering that the power of the source is measured in W (watts), then the
intensity of power for unit area at distance
r
is
I
r
2
.
¼
W
/
4
π
9.2.1.13 Sound Intensity Level
Sound intensity level (IL or
L
i
) is defined as the difference between
sound
or
acoustic intensity
and a reference value of 10
12
W/m
2
. This value, which
represents the sound intensity level (IL), can be converted to dB:
dB
I
I
0
Lw
¼
10 log
10
the reference value (10
12
W/m
2
)
where
I
¼
acoustic intensity
and
I
0
¼
If for instance the power source is
¼
0.5 W, at 5 m of distance the intensity
would be
I
5
2
0.00159 W/m
2
and the
¼
0.5/4
3.14
¼
10
3
10
12
1
:
59
IL dB
ðÞ¼
10 log
10
9.2.1.14 Sound Exposure Level
Sound exposure level (SEL) is the measure of the energy of a sound and is the time-
integral of the instantaneous squared sound pressure normalized to a square refer-
ence measure in a 1-s period.
s
Z
T
2
SEL
¼
xt
ðÞ
d
t
0
This formula can be expressed also as SEL
¼
SPL (rms) + 10*log (duration).
9.2.1.15 Loudness
Loudness is an important characteristic of a sound as it is perceived by the human
ear. Loudness is correlated to the amplitude of a sound and is defined as “that
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