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An approximation of the continuous exponential averaging
the system Operate in real time from 50 Hz is represented by the following equation for a four sample
to at least 12 kHz inclusive. This requirement applies to averaging process for k = 4:
all operating channels of a multichannel spectral analysis
system.
3.7.3 The one-third octave band analysis system shall at
least conform to the class 2 electrical performance requirements
of IEC 612604 as amended, over the range of one-third
octave nominal midband frequencies from 50 Hz to 10 kHz
inclusive.
Note.-Tests of the one-third octave band analysis system
should be made according to the methods described in
ZEC 6126@ or by an equivalent procedure approved by the
certificating authority, for relative attenuation, anti-aliasing
filters, real-tittle operation, level liriearity, and$lter integruted
response (efective bandwidth).
Ls(i,k ) = 10 lo [(0 1 3) 10 0.1L[i'(k-3+)1
(0.21) 10 o.~L[~.(*+-% i0I.0 .27) 10 o.w,(~-~+) I
(0.39) 10 O.lL[i,kl]
where L,(i,k) is the simulated SLOW weighted sound pressure
level and L(i,k) is the as-measured 0.5 seconds time average
sound pressure level determined from the output of the analyser
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 0.5 seconds data samples,
or for times greater than 2.5 seconds after initiation of data
analysis.
Note.- The coeflcients in the two equations were calcu-
4. IEC 61260:1995 entitled ''~lectroacousti-~s octave-band and lated for use in determining equivalent SLOW weighted sound
fractional-octave-bandf ilters7', This IEC publication may be pressure level~fi.0ms ~tnploef~ 0 .5 seconds time average sound
obtained from the Central Office of the International Electrotech- pressure levels. The equations should not be used with data
nical Commission, 3 rue de VarembC, Geneva, Switzerland. samples where the averaging time differs from 0.5 seconds.
APP 2-7 24/11/05
Annex 16 - Environmental Protection Volume I
3.7.6 The instant in time by which a SLOW time weighted
sound pressure level is characterized shall be 0.75 seconds
earlier than the actual readout time.
Note.- The definition of this instant in time is required to
correlate the recorded noise with the aircrajlposition when the
noise was emitted and takes into account the averagingperiod
of the SLOW weighting. For each one-halfsecond data record
this instant in time may also be identij?ed as 1.25 seconds after
the start of the associated 2 seconds averaging period.
3.7.7 The resolution of the sound pressure levels, both
displayed and stored, shall be 0.1 dB or better.
3.8 Calibration systems
The acoustical sensitivity of the measurement system shall be
determined using a sound calibrator generating a known sound
pressure level at a known frequency. The sound calibrator shall
at least conform to the class 1L requirements of IEC 60942~
as amended.
3.9 Calibration and
checking of system
3.9.1 Calibration and checking of the measurement
system and its constituent components shall be carried out to
the satisfaction of the certificating authorities by the methods
specified in 3.9.2 to 3.9.10. The calibration adjustments, including
those for environmental effects on sound calibrator output
level, shall be reported to the certificating authority and applied
to the measured one-third octave sound pressure levels determined
from the output of the analyser. Data collected during an
overload indication are invalid and shall not be used. If the
overload condition occurred during recording, the associated
test data shall be considered as invalid, whereas if the overload
occurred during analysis, the analysis shall be repeated with
reduced sensitivity to eliminate the overload.
3.9.2 The free-field frequency response of the microphone
system may be determined by using an electrostatic
actuator in combination with the manufacturer's data or by
testing in an anechoic free-field facility. The correction for frequency
response shall be determined within 90 days of each
test series. The correction for non-uniform frequency response
of the microphone system shall be reported to the certificating
authority and applied to the measured one-third octave band
sound pressure levels determined from the output of the
analyser.
5. IEC 60942: 1997 entitled "Electroacoustics - Sound calibrators".
This IEC publication may be obtained from the Central Office of
the International Electrotechnical Commission, 3 rue de VarembC,
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