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TRG-TRC007-EN 49
period four
Equipment Sound Rating
notes
This type of relationship between distance and surface area provides the
following simple mathematical model for estimating how sound will change
as the distance from the source increases.
L
p2
= L
p1
- 20 log
10
[r
2
/ r
1
]
where,
L
p2
= sound-pressure level at distance r
2
L
p1
= sound-pressure level at distance r
1
r
1
= distance from the source where L
p1
was measured
r
2
= distance from the source to where the sound pressure (L
p2
) is desired
Using this expression, it can be shown that doubling the distance from the
sound source results in a 6 dB reduction in the sound-pressure level. This is a
handy fact to know when making estimates of outdoor sound levels.
L
p2
= L
p1
- 20 log
10
[2
/1] = L
p1
- 6
Distance Correction in a Free Field
r
2
r
1
L
p2
= L
p1
– 20 log
10
Figure 54