Item 2 in the figure is the PWL of roof-radiated
bands should be improved sufficiently to eliminate
noise obtained with the use of equation 33, using
the calculated noise excess completely. This final
the TL of 2-in. dense plaster and an area of 40 x 50
step in the total analysis should assure a satisfacto-
2
= 2000 ft. Comparison of Items 10 and 12 shows
ry noise design for the complete installation.
that roof-radiated noise is also about 20 to 30 dB
4-3. Example of an on-grade packaged gas
below NC25 indoor sound levels at the base
turbine generator plant.
housing.
(e) This completes the basic analysis of the
The gas turbine generator plant plays an increas-
community noise obtained from each noise source
ingly prominent role in out-of-the-way locations for
of group of noise sources considered in this sample
both continuous and peak-load applications. Its rel-
calculation. One final check is required of the en-
ative portability means that it can be moved in and
tire plant. When the analysis is completed on each
set up almost anywhere power is needed, but, by
individual source radiating toward the housing, and
the same token, its light weight makes it a poten-
suitable noise control measures are tentatively se-
tial noise problem. The gas turbine is basically a
lected for each source, a final analysis should be
very noisy device, and the simple cabinet-like en-
made of the entire plant. All sources together must
closure and the all-too-frequent shortage of ade-
not exceed the noise criterion in all octave bands.
quate mufflers do not always control the noise.
If a few sources combine to produce excessive
a. Description of power plant. In this example, a
noise in one or more octave bands, the noise con-
15-MW plant is supplied by the manufacturer in a
trol treatments for those sources in those octave
packaged form as shown in figure 429.
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