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Note 2.- It is not necessary to include microphone extension
cables as configured in the field.
3.6.6 On the reference level range, the level corresponding
to the calibration sound pressure level shall be at least 5 dB, but
no more than 30 dB less han the upper boundary of the level
range.
3.6.7 The linear operating ranges on adjacent level ranges
shall overlap by at least 50 dB minus the change in attenuation
introduced by a change in the level range controls.
Note.- It is possible for a measurement system to have level
range controls that permit attenuation changes oj for example,
either 10 dB or I dB. mth I0 dB steps, the minimum overlap
required would be 40 dB, and with I dB steps the minimum
overlap would be 49 dB.
3.6.8 Provision shall be made for an overload indication
to occur during an overload condition on any relevant level
range.
microphone preamplifier, and any other signal-conditioning
elements that are considered to be part of the microphone sys- 3. IEC 61265:1995 entitled "Electroacoustics - Instruments for
tem, at one-third octave nominal midband frequencies of 50 Hz, smyesatesmurse mto emnte oasf uareir cornaeft- thnirodi-soec t-ave P hearfnodr msoaunncde prreeqsusiurreem leevnetsl sf oinr
1 kHz and 10 kHz, and the calibration check frequency, if it is noise certification of transport-category aeroplanes". This IEC
not one of these frequencies, the level non-linearity shall not publication may be obtained from the Central Office of the Interexceed
*0.5 dB for a linear operating range of at least 50 dB national Electrotechnical Commission, 3 rue de Varembt, Geneva,
below the upper boundary of the level range. Switzerland.
24/11/05 APP 2-6
Appendix 2 Annex 16 - Environmental Protection
3.6.9 Attenuators included in the measurement system to
permit range changes shall operate in known intervals of
decibel stcps.
3.7 Analysis systems
3.7.1 The analysis system shall conform to the specifications
in 3.7.2 to 3.7.7 for the frequency bandwidths, channel
configurations and gain settings used for analysis.
3.7.2 The output of the analysis system shall consist of
one-third octave band sound pressure levels as a function of
time, obtained by processing the noise signals @referably
recorded) through an analysis system with the following
characteristics:
a) a set of 24 one-third octave band filters, or their equivalent,
having nominal midband frequencies from 50 Hz
to 10 kHz inclusive;
b) response and averaging properties in which, in principle,
the output from any one-third octave filter band is
squared, averaged and displayed or stored as timeaveraged
sound pressure levels;
C) the interval between successive sound Dressure level
3.7.4 When SLOW time averaging is performed in the
analyser, the response of the one-third octave band analysis
systcr~lto a sudden onset or interruption of a constant sinusoidal
signal at the respective one-third octave nominal midband
frequency shall be measured at sampling instants 0.5, 1, 1.5
and 2 seconds after the onset and 0.5 and 1 seconds afler interruption.
The rising response shall be -4 * 1 dB at 0.5 seconds,
-1.75 + 0.75 dB at 1 second, -1 +C 0.5 dB at 1.5 seconds and
-0.5 * 0.5 dB at 2 seconds relative to the steady-state level.
The falling response shall be such that the sum of the output
signal levels, relative to the initial steady-state level, and the
corresponding rising response reading is^-6.5 +C I dB, at both
0.5 and 1 seconds. At subsequent times the sum of the rising
and falling responses shall be -7.5 dB or less. This equates to
an exponential averaging process (SLOW weighting) with a
nominal 1 -second time constant (i.e. 2 seconds averaging time).
3.7.5 When the one-third octave band sound pressure
levels are determined from the output of the analyser without
SLOW time weighting, SLOW time weighting shall be simulated
in the subsequent processing. Simulated SLOW weighted
sound pressure levels can be obtained using a continuous
exponential averaging process by the following equation:
L,(i, k) = 10 log [(0.60653) 10 O.lLs[i,(k-+l)l
(0.39347) lo0.' L(i,k)]
be 500 ms ' ms for specwl where L3(i,k) is the simulated SLOW weighted sound pressure
with or without SLOW time weighting; level and L(.i ,k,) is the as-measured 0.5 seconds time average -
sound pressure level determined from the output of the analyser
d) for those analysis systems that do not process the sound for the k-th instant of time and the i-th one-third octave band.
pressure signals during the period of time required for For k = 1, the SLOW weighted sound pressure L,[i,(k-1 = O)] on
rsehaadllo unto ta nexdcfoeer dre as edttuirnagt ioofn tohfe 5a nmalsy; saenr,d t he loss of data the right-hand side shall be set to dB.
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