Item 13 shows an indoor noise excess of 3 to 6 dB in
ly continuous use, external noise sources will not
the 125- to 1000-HZ octave bands. This would be
be as noisy when heard indoors. These various con-
rated as "marginal". If the NC25 criterion is a
ditions could be used to support or justify adjust-
ments to the NC criterion. In the present problem,
justified choice, these noise excesses should not be
permitted. A number of other factors could influ-
it is assumed that such factors have already been
considered, and the NC25 selection is a valid
ence the decision. If the housing is exposed to
choice.
other uncontrollable excess noise (such as nearby
(c) A CNR analysis should be carried out as
highway activity or base aircraft activity), power
a means of checking or confirming the expected re-
plant noise might not appear so noticeable. How-
action of the housed personnel to the power plant
ever, if the base is located in a very quiet suburban
noise. The N&V manual (para. 33c) summarizes
or rural area, with very little other noise, the pow-
the procedure. Figure 424 shows the CNR grid
er plant noise will be very noticeable. If the base is
upon which the outdoor power plant SPLs are
located in a very hot or very cold region, year-
plotted (taken from Item 8 of fig. 423). A noise
round, and the windows are kept closed most of the
level rank of "e" is obtained.
time, and if inside sources, such as air conditioners
or central heating and cooling systems, are in near-
4-35
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