about 11 dB at 10-ft. distance and at 14-ft. dis-
In Item 4 of figure47, Surface ''A'' is the Mainte-
nance Shop wall, at a distance of about 10 ft. to the
tance. Thus, the SPL reduction for Item 6 would
be 3 dB (from 8 dB down to 11 dB) at 31 Hz.
acoustic center of the nearest engine, and Surface
The SPL reduction increases gradually at the
"B" is the upper-level Control Room wall, at a dis-
higher R values in the higher octave bands. Item 7
tance of about 14 ft. to the acoustic center of the
then gives the SPL estimated at the engine room
engine. Item 5 is filled in with the R values of fig-
side of the Maintenance Shop wall and the Control
ure 45. Item 6 is obtained from figure 51 of the
Room wall.
N&V manual by taking the SPL reduction (going
(c) The procedure of (b) above is somewhat
"down" on the graph) from the 3-ft. starting dis-
tedious, although correct. The procedure can be
tance out to the 10-ft. and 14-ft. wall distances,
shortened with certain adaptations of the data
along the lines representing the Room Constant
form. Figure 4-8 shows the simplified (and still
values of the various octave bands. Thus, for R =
2
correct) version.
660 ft. (in the 31-Hz band), the REL SPL of figure
51 drops from about 8 dB at 3-ft. distance to
4-11
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