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HW #2
FUNDAMENTALS & SOUND LEVEL
Answer Key
1)
Speed of Sound, Frequency, and Wavelength
λ
⋅
=
f
V
…….
①
V
= speed of sound,
f
= frequency,
λ
= wavelength
2)
Sound Intensity & Inverse Square Law
2
4
d
W
I
π
=
2
1
2
2
2
1
d
d
I
I
=
…….
②
d
: distance
3)
Sound Intensity Level
0
log
10
I
I
L
I
=
…….
③
I
= intensity, W/m
2
I
0
= 10
12
W/m
2
, the threshold of hearing
1.
Find the corresponding wavelength of sound at each of the following frequencies. Suppose that the speed of
sound in air is 1,000 ft/sec.
1) 20 Hz
2) 250 Hz
3) 1000 Hz
By the equation
①
,
1)
=
=
=
20
1000
f
V
50 ft
2)
=
=
250
1000
4 ft
3)
=
=
1000
1000
1 ft
2.
Sound energy requires a medium in which to travel – from one point in the medium to another. The speed of
sound is dependent upon density of the medium and other ambient conditions such as temperature and
humidity. Discuss how the speeds of sound may be different with each other in air, steel, and in concrete if
the ambient conditions are constant.
In general, the density of air is a lot lower than the density of steel or concrete, and the density of
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 Fall '08
 Staff

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