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Geneva, Switzerland.
3.9.3 When the angles of incidence of sound emitted from
the aircraft are within &3O0 of grazing incidence at the microphone
(see Figure A2-l), a single set of fiee-field corrections
based on grazing incidence is considered sufficient for correction
of directional response effects. For other cases, the angle
of incidence for each one-half second sample shall be
determined and applied for the correction of incidence effects.
3.9.4 For analogue magnetic tape recorders, each reel of
magnetic tape shall carry at least 30 seconds of pink random or
pseudo-random noise at its beginning and end. Data obtained
from analogue tape-recorded signals shall 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.
3.9.5 The frequency response of the entire measurement
system while deployed in the field during the test series, exclusive
of the microphone, shall 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. The output of the noise generator shall be determined by
a method traceable to a national standards laboratory within
six months of each test series, and tolerable changes in the
rclativc output from thc prcvious calibration at each one-third
octave band shall be not more than 0.2 dB. The correction for
frequency response shall be reported to the certificating
authority and applied to the measured one-thud octave sound
pressure levels determined from the output of the analyser.
3.9.6 The performance of switched attenuators in the
equipment used during noise certification measurements and
calibration shall be checked within six months of each test
series to ensure that the maximum error does not exceed
0.1 dB.
3.9.7 The sound pressure level produced in the cavity of
the coupler of the sound calibrator shall be calculated for the
test environmental conditions using the manufacturer's supplied
information on the influence of atmospheric air pressure and
temperature. The sound pressure level shall be used to establish
the acoustical sensitivity of the measurement system. The
output of the sound calibrator shall be determined by a method
traceable to a national standards laboratory within six months of
each test series and tolerable changes in output from the
previous calibration shall be not more than 0.2 dB.
3.9.8 Sufficient sound pressure level calibrations shall be
made during each test day to ensure that the acoustical sensitivity
of the measurement system is known at the prevailing
environmental conditions corresponding with each test series.
The measurement system shall be considered satisfactory if the
difference is not greater than 0.5 dB between the acoustical
sensitivity levels recorded immediately before and immediately
after each test series on a given day. The 0.5 dB limit
applies after any atmospheric pressure corrections have been
determined for the calibrator output level. The arithmetic mean
24/11/05 APP 2-8
Appendix 2 Annex 16 - Environmental Protection
of the before and after measurements shall be used to represent
the acoustical sensitivity level of the measurement system for
that test series. The calibration corrections shall be reported to
the certificating authority and applied to the measured onethird
octave band sound pressure levels determined from the
output of the analyser.
3.9.9 Each recording medium, such as a reel, cartridge,
cassette, or diskette, shall cany a sound pressure level calibration
of at least 10 seconds duration at its beginning and end.
3.9.10 The free-field insertion loss of the windscreen for
each one-third octave nominal midband frequency from 50 Hz
to 10 kHz inclusive shall be determined with sinusoidal sound
signals at appropriate incidence angles on the inserted microphone.
For a windscreen which is undamaged and uncontaminated,
the insertion loss may be taken ffom the manufacturer's
data. In addition, the insertion loss of the windscreen may be
determined by a method traceable to a national standards laboratory
within six months of each test series, and tolerable
changes in the insertion loss from the previous calibration at
each one-third octave frequency band shall be not more than
0.4 dB. The correction for the free-field insertion loss of the
windscreen shall be reported to the certificating authority and
　
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