orous steps, and a few of these are included in the
escaping outside and through the two walls to the
example--largely to demonstrate that such ap-
Control Room should be evaluated and compared
proaches must sometimes be taken when exactness
with the applicable criteria. For both the Engine
is not possible.
Room and the Generator Room, the escaping noise
b. Data forms are used freely throughout this
through the ventilation openings should be checked
and the N&V manual to show that they are simple
(including the noise of the 30-hp fans), and the in-
to use, that they remind the user of many key
sertion losses of the wall- and roof-mounted muf-
steps in the calculation procedures, that they pro-
flers estimated. The total noise from all sources
vide documentation of the rationale and data used
must be kept at or below the PWL criterion evalu-
to arrive at acoustic designs, and that they are suf-
ated in figure 432. The external side walls of the
ficiently flexible to be adapted to slightly different
intake and exhaust stack must have adequate TL
conditions from those for which they were de-
(transmission loss) so that noise does not escape
signed. Blank copies of the data forms developed
through these side-wall flanking paths. The TL of
for this and the N&V manual are reproduced in ap-
the side walls should be at least 10 dB greater than
pendix A. These forms may be duplicated and used
the insertion loss of the muffler (para. 34a).
to analyze and document the various steps in
Finally, for conservation of hearing, personnel
acoustic designs covered by these manuals.
should be admitted into the Engine Room and Gen-
erator Room only when wearing adequate hearing
c. A dilemma that might be brought on by the
protection, possibly consisting of both ear plugs
manual is the impasse which could develop when
and ear muffs. SPLs inside the Engine Room may
manufacturers state that their equipment or sound
exceed 110 to 115 dB in the upper octave bands if
control devices perform better acoustically than is
the engines do not have noise-reducing covers.
assumed here. If this situation should arise, it is
Suitable labeling of the noise-hazardous areas
important to receive some form of guaranteed as-
should be included in the design of the plant.
surance in writing (accompanied by valid test data
carried out by a reputable and disinterested organ-
ization) that the manufacturer will back up the
4-4. Summary and conclusions.
claims.
a. The specific examples illustrated in this chap-
d. The procedures used in these manuals have
ter and the generalized applications given in the
evolved over the past 20 to 30 years of applied
N&V manual show the various calculable steps in-
acoustics in the United States and have been used
volved in the analysis of a wide variety of noise
successfully to evaluate and solve many types of
problems and solutions. Some of the acoustic analy-
noise problems. The data and procedures are rec-
ses are quite simple and straightforward, and the
ommended for use by engineers, architects, and
results are quite reliable. However, some of the
planners of military installations as well.
analyses involve approximations and a few nonrig-
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