b. PWL criterion for noise to hospital. It is first
This plant is to be located 1600 ft. from a military
base hospital, and it is the designer's responsibility
required to estimate the total PWL of the power
to specify the acoustic requirements of the pack-
plant that will just produce acceptable sound levels
aged generator. The gas turbine power output
inside the hospital building at a distance of 1600-ft.
shaft, operating at 7200 rpm, drives a gear which
An indoor criterion of NC20 for patient rooms is
in turn drives a generator at 3600 rpm. The Engine
wanted. This low level is selected to help reduce
Room and the Generator Room are ventilated by
the audibility of the tonal sounds of the plant. The
30-hp fans, as seen in the exhaust vents of these
hospital is fitted with sealed-closed windows, with
two rooms in figure 43. The manufacturer pro-
each room receiving some fresh air through small
vides a housing for the entire unit that is made of
wall vents to the outside (similar to wall type C in
l/16-in. -thick sheet steel with a 4-in .-thick absorb-
the N&V table 610). There is a tall growth of me-
ent lining on the inside, covered with 22-gauge per-
dium dense woods between the power plant and the
forated sheet steel. Consideration should be given
hospital. The woods are about 500 ft. deep, and the
to the following parts of the noise problem: Muffler
trees are about 40 ft. high. The top of the exhaust
requirement and design for the air inlet to the en-
stack of the power plant is about 30 ft. above ground
gine, muffler requirement and design for the en-
elevation, and the upper windows of the two-floor
gine exhaust, noise escape from the walls and roof
hospital buildings are about 25 ft. above ground.
of the entire package, noise escape from the venti-
The approximate insertion loss of the woods is esti-
lation openings of the Engine and Generator
mated with the use of DD Form 2300 (Elevation
Rooms, hearing protection for operators, when
Profile Between Sound Source and Receiver Posi-
necessary, and acceptable noise levels in the Con-
tion) and DD Form 2301 (Estimation of Insertion
trol Room. In this sample problem, only the intake
Loss of Vegetation in Outdoor Sound Path). Fig-
and exhaust muffler requirements are evaluated.
ures 430 and 431 are filled-in copies of these two
Details of the other parts of the total study would
data forms.
follow along the lines of the example given in detail
in paragraph 42.
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