TM
5805-9/AFM
88201NAVFAC
DM3.14
CHAPTER 2
SOUND ANALYSIS PROCEDURE
a. Step 1, source data.
2-1. Contents of chapter.
(1) The sound power levels (PWLs) of the en-
This chapter summarizes the four basic steps for
gine noise sources are given below in paragraphs
evaluating and solving an engine noise problem.
27 and 28. Sound pressure levels (SPLs) or
The steps involve sound level data for the source,
sound power levels of some auxiliary sources may
sound (and vibration) criteria for inhabited spaces,
be found in -chapter 7 of the N&V manual, or may
the fundamentals of sound travel (both indoors and
have to be obtained from the literature or from the
outdoors), and knowledge and use of sound (and vi-
equipment manufacturers.
bration) treatments to bring the equipment into
(2) Detailed procedures for converting PWL
conformance with the criteria conditions applicable
data to SPL data and for estimating the SPL of a
to the work spaces and neighboring areas. Much of
source at any receiver position of interest indoors
this material is discussed in detail in the N&V
or outdoors are given in chapters 5 and 6 of the
manual, but brief summaries of the key items are
N&V manual.
listed and reviewed here. Special noise- and vibra-
(3) Where several noise sources exist, the ac-
tion-control treatments (beyond the normal uses of
cumulated effect must be considered, so simple
walls, structures, and absorption materials to con-
procedures are given (Appendix B of the N&V
tain and absorb the noise) are discussed in chapter
manual) for adding the contributions of multiple
3, and examples of the analysis procedure are giv-
noise sources by "decibel addition. "
en in chapter 4.
b. Step Z, criteria.
(1) Applicable criteria are discussed in the
N&V manual (chap. 3 for sound and chap. 4 for vi-
22. General procedure.
bration) and are summarized in paragraphs 2-3 and
In its simplest form, there are four basic steps to
24 below for most situations in which an intruding
evaluating and solving a noise problem. Step 1 re-
or interfering noise may influence an acoustic envi-
quires the estimation or determination of the noise
ronment (hearing damage due to high noise levels,
levels produced by a noise source at the particular
interference with speech, interference with tele-
point of interest, on the initial assumption that no
phone use and safety or warning signals, and noise
special acoustic treatment is used or required. Step
annoyance at work and at home).
2 requires the establishment of a noise level crite-
(2) In a complex problem, there may be a mul-
rion considered applicable for the particular point
tiplicity of criteria as well as a multiplicity of
of interest. Step 3 consists of determining the
sources and paths. An ultimate design might have
amount of "excess noise" or the "required noise re-
to incorporate simultaneously a hearing protection
duction" for the problem. This reduction is simply
criterion for one operator, reliable speech or tele-
the algebraic difference, in decibels, between the
phone communication for another operator, accept-
noise levels produced by the equipment (step 1
able office noise levels for other personnel, and ac-
above) and the criterion levels desired for the re-
ceptable sleeping conditions for still other
gion of interest (step 2 above). Step 4 involves the
personnel.
design or selection of the acoustic treatment or the
c. Step 3, noise reduction requirements.
architectural structure that will provide the "re-
(1) The required noise reduction is that
quired noise reduction (step 3 above). This basic
amount of noise level that exceeds the applicable
procedure is carried out for each octave frequency
criterion level. Only simple subtraction is involved,
band, for each noise source if there are several
but, again, it is essential that all noise sources be
sources, for each noise path if there are several
considered at each of the various criterion
possible paths, and for each point of interest that
situations.
receives the noise. The basic procedure becomes
(2) Some noise sources are predominantly of
complicated because of the multiplicity of all these
high-frequency content and add little low-
factors. The ultimate success of the design depends
frequency noise to the problem, while others are
largely on devising adequate practical solutions,
predominantly low-frequency. Thus, frequency
but it also requires that a crucial noise source,
content by octave bands is important in determin-
path, or receiver has not been overlooked. Addi-
ing the portion of excess noise contributed by a
tional details that fall under these four steps follow
given source.
immediately.
2-1
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