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from something other than (or in addition to) an actual tone (or
any spectral irregularity other than aeroplane noise), an additional
analysis shall be made using a filter with a bandwidth
narrower than one-third of an octave. If the narrow band analysis
corroborates these suspicions, then a revised value for the
background sound pressure level, SPLV(i,k), shall be determined
from the narrow band analysis and used to compute a
revised tone correction factor for that particular one-third
octave band.
4.4 Maximum tone corrected
perceived noise level
4.4.1 The maximum tone corrected perceived noise level,
PNLTM, shall be the maximum calculated value of the tone
corrected perceived noise level PNLT(k). It shall be calculated
in accordance with the procedure of 4.3. To obtain a satisfactory
noise time history, measurements shall be made at
half-second time intervals.
Note.- Figure A1-2 is an example of aflyover noise time
history where the maximum value is clearly indicated.
4.4.2 If there are no pronounced irregularities in the spectrum,
even when examined by a narrow band analysis, then the
procedure of 4.3 shall be disregarded since PNLT(k) would be
identically equal to PNL(k). For this case, PNLTM shall be the
maximum value of PNL(k) and would equal PNLM.
4.5 Duration correction
Step 8. Calculate the differences, F(i,k), between the original 4.5.1 The duration correction factor, D, determined by the
sound pressure level and the fmal background sound pressure integration technique shall be defined by the expression:
level as follows:
F(i,k) = SPL(i,k) - SPL"(i, k)
and note only values equal to or greater than three.
Step 9. For each of the relevant one-third octave bands (3
to 24), determine tone correction factors from the sound where T is a normalizing time constant, and PNLTM is the
pressure level differences, F(i,k), and Table A 1-2. maximum value of PNLT.
APP 1-9 24/11/05
Annex 16 - Environmental Protection Volume 1
Table A1-3. Example of tone correction calculation for a turbofan engine
-
Band f SPL S 1ASI SPL' S' S SPL" F C
(i) Hz dB dB dl3 dB dB dB dB dB dB
Step S;P Step Step Step Step Step Step
1 4 5 6 7 8 9
I50 - - - - - - - - - 1
1 step 1 @(I) - @(i - 1) 1 1 step 6 [@(i)+ @(i+ 1)+1
step 2 @ti)- @(i- 111 1
Step 3 see instructions
~ -
see instructions
Step 7 @(i- I)+ @(i- 1
( step 8 00-) @ (i)
1 step 9 see Table A1-2 1
APP 1-10
Appendix 1 Annex 16 - Environmental Protection
4.5.1.1 If PNLTM is greater than 100 TPNdB. t(l) shall
be the first point of time after which PNLT becomes greater
than PNLTM - 10 and t(2) shall be the point of time after
which PNLT remains constantly less than PNLTM - 10.
4.5.1.2 If PNLTM is less than 100 TPNdB, t(1) shall be
the first point of time after which PNLT becomes greater than
90 TPNdB and t(2) shall be the point of time after which
PNLT remains constantly less than 90 TPNdB.
4.5.1.3 If PNLTM is less than 90 TPNdB, the duration
correction shall be taken as equal to 0.
4.5.2 Since PNLT is calculated from measured values of
SPL, there will, in general, be no obvious equation for PNLT
as a function of time. Consequently, the equation shall be
rewritten with a summation sign instead of an integral sign as
follows:
1 d/At
At. antilog -
where At is the length of the equal increments of time for
which PNLT(k) is calculated and d is the time interval to the
nearest 1.0 second during which PNLT(k) remains greater or
equal either to PNLTM - 10 or to 90 according to the cases
specified in4.5.1.1 to 4.5.1.3.
4.5.3 To obtain a satisfactory history of the perceived
noise level,
a) half-second time intervals for At, or
b) a shorter time interval with approved limits and constants,
shall be used.
4.5.4 The following values for T and At shall be used in
calculating D in the procedure given in 4.5.2:
T = 10 s, and
At = 0.5 s
Using the above values, the equation for D becomes
I 2d
D = 10 log C antilog P-NLT(k) I - PNLTM - 13
10
where the integer d is the duration time defined by the points
corresponding to the values PNLTM - 10 or 90 as the case
may bc.
4.5.5 If in the procedures given in 4.5.2, the limits of
PNLTM - 10 or 90 fall between the calculated PNLT(k)
values (the usual case), the PNLT(k) values defining the
t;' Z
a -
-E
.3- e
PNLTM
4
-
t(2)
Flyover time t, seconds
Figure A1-2. Example of perceived noise level corrected for tones
as a function of aircraft flyover time
APP 1-11
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