Comparison of the SPLs in Items 10 and 12 shows
than that of 4-in.-thick dense concrete (N&V table
that the noise radiated by the wall will fall about 20
58), whichever is less. Equation 33 is used here
to 30 dB below the NC25 indoor criterion levels.
to obtain the PWL radiated separately by each En-
Thus, wall-radiated noise will be of no concern in
gine Room roof. Then, the directivity loss in the
horizontal direction is applied, using table 3-1. The
this sample problem.
power plant building has a parapet, so it qualifies
(d) Engine noise escaping through the room
should be checked in accordance with paragraph
as a Type 1 roof, and the smaller D dimension of
32d. The roof deck for the building is of 2-in. -
each Engine Room is 40 ft., so the column of
thick poured concrete on corrugated metal. The TL
directivity corrections for "D under 50 ft. " should
of the roof deck is estimated to be about the same
be used. Each Engine Room has different sound
sources, so the effect of each roof section must be
as that of 2-in. -thick dense plaster (N&V table
511) or about 4 dB less than that of 4-in. -thick
calculated. Only one roof (for Engine Room No. 2)
is illustrated in figure 428.
dense plaster (N&V table 5ll) or about 5dB less
4-41
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