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 (SPL1) of a source at distance d1 is known, the sound pressure level (SPL2) at distance d2 can be found as follows:
If the sound pressure level (SPL1) at 21 meters (d1) is 100 dB(A), then at 7 meters (d2) the sound pressure level (SPL2) 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)
PAGE 30 — INDUSTRIAL GENERATOR SETS — APPLICATION & INSTALLATION MANUAL — REV. #4 (09/07/07)
