A36.4.1.3 The calculation procedure that
uses physical measurements of noise to derive the EPNL evaluation measure of subjective response consists of the following five
steps:
(a) The 24 one-third octave bands of sound
pressure level are converted to perceived
noisiness (noy) using the method described
in section A36.4.2.1 (a). The noy values are
combined and then converted to instantaneous perceived noise levels, PNL(k).
(b) A tone correction factor C(k) is calculated for each spectrum to account for the
subjective response to the presence of spectral irregularities.
(c) The tone correction factor is added to
the perceived noise level to obtain tone-corrected perceived noise levels PNLT(k), at
each one-half second increment:
PNLT(k) = PNL(k) + C(k)
The instantaneous values of tone-corrected
perceived noise level are derived and the
maximum value, PNLTM, is determined.
(d) A duration correction factor, D, is computed by integration under the curve of tonecorrected perceived noise level versus time.
(e) Effective perceived noise level, EPNL,
is determined by the algebraic sum of the
maximum tone-corrected perceived noise
level and the duration correction factor:
EPNL = PNLTM + D
A36.4.2 Perceived noise level.
A36.4.2.1 Instantaneous perceived noise levels, PNL(k), must be calculated from instantaneous one-third octave band sound pressure levels, SPL(i, k) as follows:
(a) Step 1: For each one-third octave band
from 50 through 10,000 Hz, convert SPL(i, k)
to perceived noisiness n(i, k), by using the
mathematical formulation of the noy table
given in section A36.4.7.
(b) Step 2: Combine the perceived noisiness
values, n(i, k), determined in step 1 by using
the following formula:

 - 
 - - 24
-
N (k) = n (k) + 0.15 -  -  n (i, k)-  -  n ( k )-
 - 
 - - i =1
-
24

= 0.85 n ( k ) + 0.15 -  n (i, k )

spaschal on DSK3GDR082PROD with CFR

i =1
where n(k) is the largest of the 24 values of
n(i, k) and N(k) is the total perceived
noisiness.
(c) Step 3: Convert the total perceived
noisiness, N(k), determined in Step 2 into
perceived noise level, PNL(k), using the following formula:

PNL (k) = 40.0 +

10
log N (k)
log 2

NOTE: PNL(k) is plotted in the current advisory circular for this part.
A36.4.3 Correction for spectral irregularities.
A36.4.3.1 Noise having pronounced spectral
irregularities (for example, the maximum
discrete frequency components or tones)
must be adjusted by the correction factor
C(k) calculated as follows:
(a) Step 1: After applying the corrections
specified under section A36.3.9, start with the
sound pressure level in the 80 Hz one-third
octave band (band number 3), calculate the
changes in sound pressure level (or  - slopes - )
in the remainder of the one-third octave
bands as follows:
s(3,k) = no value
s(4,k) = SPL(4,k)SectionSPL(3,k)
-
-
s(i,k) = SPL(i,k)SectionSPL(iSection1,k)
-
-
s(24,k) = SPL(24,k)SectionSPL(23,k)
(b) Step 2: Encircle the value of the slope,
s(i, k), where the absolute value of the
change in slope is greater than five; that is
where:
|Ds(i,k)| = |s(i,k)Sections(iSection1,k)|>5
(c) Step 3:
(1) If the encircled value of the slope s(i, k)
is positive and algebraically greater than the
slope s(iSection1, k) encircle SPL(i, k).
(2) If the encircled value of the slope s(i, k)
is zero or negative and the slope s(iSection1, k) is
positive, encircle SPL(iSection1, k).
(3) For all other cases, no sound pressure
level value is to be encircled.
(d) Step 4: Compute new adjusted sound
pressure levels SPL-(i, k) as follows:
(1) For non-encircled sound pressure levels,
set the new sound pressure levels equal to
the original sound pressure levels, SPL-(i, k)
= SPL(i, k).
(2) For encircled sound pressure levels in
bands 1 through 23 inclusive, set the new
sound pressure level equal to the arithmetic
average of the preceding and following sound
pressure levels as shown below:
SPL-(i,k) = 1-2[SPL(iSection1,k) + SPL(i + 1,k)]
(3) If the sound pressure level in the highest frequency band (i = 24) is encircled, set
the new sound pressure level in that band
equal to:
SPL-(24,k) = SPL(23,k) + s(23,k)
(e) Step 5: Recompute new slope s-(i, k), including one for an imaginary 25th band, as
follows:
s-(3,k) = s-(4,k)
s-(4,k) = SPL-(4,k)SectionSPL-(3,k)
-
-
s-(i,k) = SPL-(i,k)SectionSPL-(iSection1,k)
-
-

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ER08JY02.002</MATH>

Pt. 36, App. A

ER08JY02.001</MATH>

Federal Aviation Administration, DOT