Item 2 is the algebraic sum of Items 3 and 4. Thus,

The NC20 acceptable indoor sound levels are first

inserted in Items 11 and 12. If the criterion levels

Item 2 represents the total PWL of the power

are met, the Item 10 values will be the same as the

plant sound that would just produce an NC20 in-

Item 12 values, so they are repeated in Item 10.

door criterion at the hospital--after traveling 1600

Item 9 shows the noise reduction of outdoor noise

ft., passing through the wooded area, and entering

coming indoors through the wall, which most near-

the hospital through the type C wall structure.

ly resembles wall type C of the N&V table 6-7.

This is--called the PWL criterion. In a real-life situ-

The allowable outdoor noise levels (Item 8) are

ation, the outdoor SPLs at the hospital (Item 8 of

figure 432) probably would not be acceptable to

then the algebraic sum of Items 9 and 10. In travel-

ing to the hospital, the sound encounters the

residential neighbors. Further, the NC20 criteri-

on levels inside the hospital would not be achieved

wooded area evaluated figures 430 and 431. For

a conservative estimate (lower value) of the inser-

inside residences, at the same distances, that have

their windows open much of the time. Thus, the

tion loss of the woods, the winter insertion loss

from figure 4-31 is used in Item 5 of figure 4-32.

problem developed here is based only on the condi-

Item 4 of figure 432 is the algebraic sum of Items

tions as defined.

5 and 8. This "tentative outdoor SPL" would have

been the same as the Item 8 values if there had

sources of a gas turbine engine are calculated with

been no woods. Item 3 is the distance term (N&V

the use of DD Form 2305. The calculation is carried

table 64 for standard-day sound propagation con-

out for this 15-MW engine in figure 433.

ditions) for the 1600-ft. distance (Item 1). Finally,