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c) recording and reproducing equipment characteristics,
frequency response, and dynamic range compatible with
the response and accuracy requirements of 3.3; and
d) acoustic calibrators using sine wave or broadband noise
of known sound pressure level. If broadband noise is
used, the signal shall be described in terms of its average
and maximum root-mean-square (rms) value of nonoverload
signal level.
3.3 Sensing, recording and
reproducing equipment
3.3.1 When so specified by the certificating authority, the
sound produced by the aeroplane shall be recorded in such a
way that the complete information, including time history, is
retained. A magnetic tape recorder is acceptable.
3.3.2 The characteristics of the complete system shall
comply with the recommendations given in International
Electrotechnical Commission (IEC) Publication No. 179l with
regard to the sections concerning microphone, amplifier and
indicating instrument characteristics. The text and specifications
of IEC Publication No. 179' entitled "Precision Sound
Level Meters" are incorporated by reference into this section
and are made a part hereof.
Note.- When a tape recorder is used, it forms part of the
complete system complying with IEC Recommendation 561.'
3.3.3 The response of the complete system to a seilsibly
plane progressive sinusoidal wave of constant amplitude shall
lie within the tolerance limits specified in Table IV and
Table V for Type I instruments in IEC Publication No. 179,'
for weighting curve "A" over the frequency range 45 to
11 200 Hz.
3.3.4 The recorded noise signal shall be read through
an "A" filter as defined in IEC Publication No. 179,' and with
dynamic characteristics designated "slow".
Note.- During tests with high flight speeds, the 'tfast"
dynamic characteristics may be necessaly to obtain the true
level.
3.3.5 The equipment shall be acoustically calibrated using
facilities for acoustic free-field calibration. The overall sensitivity
of the measuring system shall be checked before and
after the measurement of the noise level for a sequence of
aeroplane operations, using an acoustic calibrator generating a
known sound pressure level at a known frequency.
Note.- A pistonphone operating at a nominal 124 dB and
250 Hz is generally used for this purpose.
3.3.6 A wind screen shall be employed with the microphone
during all measurements of aeroplane noise when the
wind speed is in excess of 11 kmlh (6 kt). Its characteristics
shall be such that when it is used, the complete system including
the wind screen will meet the specifications above. Its
insertion loss at the frequency of the acoustic calibrator shall
also be known and included in the provision of an acoustic
reference level for the analysis of the measurements.
3.4 Noise measurement procedures
3.4.1 The microphones shall be oriented in a known
direction so that the maximum sound received arrives as
nearly as possible in the direction for which the microphones
are calibrated. The microphones shall be placed so that their
sensing elements are approximately 1.2 m (4 ft) above ground.
3.4.2 Immediately prior to and after each test, a recorded
acoustic calibration of the system shall be made in the field
with an acoustic calibrator for the two purposes of checking
system sensitivity and providing an acoustic reference level for
the analysis of the sound level data.
3.4.3 Background noise, including ambient noise and
electrical noise of the measurement systems, shall be recorded
and determined in the test area with the system gain set at
levels which will be used for aeroplane noise measurements. If
aeroplane sound pressure levels do not exceed background
sound pressure levels by at least 10 &(A), approved conections
for the contribution of background sound pressure level
to the observed sound pressure level shall be applied.
4. REPORTING OF DATA TO THE
CERTIFICATING AUTHORITY AND
CORRECTION OF MEASURED DATA
4.1 Data reporting
I . As amended. Available from the Central Office of the International 4.1.1 Measured and corrected sound pressure levels
Electrotechnical Commission, 3 rue de Varembe, Geneva, obtained with equipment conforming to the specifications
Switzerland. described in Section 3 of this appendix shall be reported.
24/11/05 APP 3-2
Appendix 3 Annex 16 - Environmental Protection
4.1.2 The type of equipment used for measurement and
analysis of all acoustic aeroplane performance and meteorological
data shall be reported.
4.1.3 The following atmospheric environmental data,
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