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PAGE 30 — INDUSTRIAL GENERATOR SETS — APPLICATION & INSTALLATION MANUAL — REV. #4 (09/07/07)
ENVIRONMENTAL CONSIDERATIONS — dB(A)
Effects of Distance
As the distance between a noise source and receiver
increases, the sound level decreases. If a second sound
measurement is taken twice as far from the source, the
second reading will be approximately 6 dB(A) less than the
first reading. If the sound pressure level (SPL
1
) of a source
at distance d
1
is known, the sound pressure level (SPL
2
) at
distance d
2
can be found as follows:
If the sound pressure level (SPL
1
) at 21 meters (d
1
) is 100
dB(A), then at 7 meters (d
2
) the sound pressure level (SPL
2
)
will be:
It should be noted the background noise level must be at
least 10 dB(A) below the noise level of the generator set,
the installation must approximate a free field environment
and the generator set must be equipped with a critical grade
muffler.
Figure 4. below can be used as an alternative to the formula
for estimating the sound level at various distances (such as
to the property line). For instance, as shown by the dashed
arrows, if the noise rating of the generator set is 95 dB(A) at
7 meters, the noise level 100 meters away will be
approximately 72 dB(A).
When using Figure 4, draw a line parallel to the slanted lines
from the known dB(A) value on the vertical scale line to the
vertical line for the specified distance. Then draw a horizontal
line back to the vertical scale line and read the new dB(A)
value.
Figure 4. Distance Effects on dB(A)