spaschal on DSK3GDR082PROD with CFR

Federal Aviation Administration, DOT

Pt. 36, App. A

the output of the analyzer without slow
time-weighting, slow time-weighting must
be simulated in the subsequent processing.
Simulated slow time-weighted sound pressure levels can be obtained using a continuous exponential averaging process by the
following equation:
Ls (i,k) = 10 log [(0.60653) 100.1 Ls[i, (kSection1)] +
(0.39347) 100.1 L (i, k)]
where Ls(i,k) is the simulated slow timeweighted sound pressure level and L(i,k)
is the as-measured 0.5s time average
sound pressure level determined from the
output of the analyzer for the k-th instant of time and i-th one-third octave
band. For k = 1, the slow time-weighted
sound pressure Ls[i, (k Section 1 = 0)] on the
right hand side should be set to 0 dB. An
approximation of the continuous exponential averaging is represented by the
following equation for a four sample
averaging process for k -4:
Ls (i,k) = 10 log [(0.13) 100.1 L[i,(kSection3)] + (0.21) 100.1
L[i, (kSection2)] + (0.27) 100.1 L[i, (kSection1)] + (0.39) 100.1 L[i,
k]]
where Ls (i, k) is the simulated slow timeweighted sound pressure level and L (i, k)
is the as measured 0.5s time average
sound pressure level determined from the
output of the analyzer for the k-th instant of time and the i-th one-third octave band.
The sum of the weighting factors is 1.0 in
the two equations. Sound pressure levels calculated by means of either equation are valid
for the sixth and subsequent 0.5s data samples, or for times greater than 2.5s after initiation of data analysis.
NOTE: The coefficients in the two equations were calculated for use in determining
equivalent slow time-weighted sound pressure levels from samples of 0.5s time average
sound pressure levels. The equations do not
work with data samples where the averaging
time differs from 0.5s.
A36.3.7.6 The instant in time by which a
slow time-weighted sound pressure level is
characterized must be 0.75s earlier than the
actual readout time.
NOTE: The definition of this instant in
time is needed to correlate the recorded
noise with the aircraft position when the
noise was emitted and takes into account
the averaging period of the slow timeweighting. For each 0.5 second data record
this instant in time may also be identified as
1.25 seconds after the start of the associated
2 second averaging period.
A36.3.7.7 The resolution of the sound pressure levels, both displayed and stored, must
be 0.1 dB or finer.
A36.3.8 Calibration systems.
A36.3.8.1 The acoustical sensitivity of the
measurement system must be determined
using a sound calibrator generating a known

sound pressure level at a known frequency.
The minimum standard for the sound calibrator is the class 1L requirements of IEC
60942 as amended (incorporated by reference,
see Section 36.6).
A36.3.9 Calibration and checking of system.
A36.3.9.1 Calibration and checking of the
measurement system and its constituent
components must be carried out to the satisfaction of the FAA by the methods specified
in sections A36.3.9.2 through A36.3.9.10. The
calibration adjustments, including those for
environmental effects on sound calibrator
output level, must be reported to the FAA
and applied to the measured one-third-octave sound pressure levels determined from
the output of the analyzer. Data collected
during an overload indication are invalid and
may not be used. If the overload condition
occurred during recording, the associated
test data are invalid, whereas if the overload
occurred during analysis, the analysis must
be repeated with reduced sensitivity to
eliminate the overload.
A36.3.9.2 The free-field frequency response
of the microphone system may be determined by use of an electrostatic actuator in
combination with manufacturer-s data or by
tests in an anechoic free-field facility. The
correction for frequency response must be
determined within 90 days of each test series.
The correction for non-uniform frequency response of the microphone system must be reported to the FAA and applied to the measured one-third octave band sound pressure
levels determined from the output of the analyzer.
A36.3.9.3 When the angles of incidence of
sound emitted from the aircraft are within
Section30Section of grazing incidence at the microphone
(see Figure A36-1), a single set of free-field
corrections based on grazing incidence is
considered sufficient for correction of directional response effects. For other cases, the
angle of incidence for each 0.5 second sample
must be determined and applied for the correction of incidence effects.
A36.3.9.4 For analog magnetic tape recorders, each reel of magnetic tape must carry at
least 30 seconds of pink random or pseudorandom noise at its beginning and end. Data
obtained from analog tape-recorded signals
will be accepted as reliable only if level differences in the 10 kHz one-third-octave-band
are not more than 0.75 dB for the signals recorded at the beginning and end.
A36.3.9.5 The frequency response of the entire measurement system while deployed in
the field during the test series, exclusive of
the microphone, must be determined at a
level within 5 dB of the level corresponding
to the calibration sound pressure level on
the level range used during the tests for each
one-third octave nominal midband frequency
from 50 Hz to 10 kHz inclusive, utilizing pink
random or pseudo-random noise. Within six
months of each test series the output of the

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