spaschal on DSK3GDR082PROD with CFR

Federal Aviation Administration, DOT

Pt. 36, App. A

system and the root mean square sound pressure that would exist at the position of the
microphone in its absence.
A36.3.1.6 Free-field sensitivity level of a microphone system means, in decibels, twenty
times the logarithm to the base ten of the
ratio of the free-field sensitivity of a microphone system and the reference sensitivity
of one volt per Pascal.
NOTE: The free-field sensitivity level of a
microphone system may be determined by
subtracting the sound pressure level (in decibels re 20 SectionPa) of the sound incident on the
microphone from the voltage level (in decibels re 1 V) at the output of the microphone
system, and adding 93.98 dB to the result.
A36.3.1.7 Time-average band sound pressure
level means in decibels, ten times the logarithm to the base ten, of the ratio of the
time mean square of the instantaneous
sound pressure during a stated time interval
and in a specified one-third octave band, to
the square of the reference sound pressure of
20 SectionPa.
A36.3.1.8 Level range means, in decibels, an
operating range determined by the setting of
the controls that are provided in a measurement system for the recording and one-third
octave band analysis of a sound pressure signal. The upper boundary associated with any
particular level range must be rounded to
the nearest decibel.
A36.3.1.9 Calibration sound pressure level
means, in decibels, the sound pressure level
produced, under reference environmental
conditions, in the cavity of the coupler of
the sound calibrator that is used to determine the overall acoustical sensitivity of a
measurement system.
A36.3.1.10 Reference level range means, in
decibels, the level range for determining the
acoustical sensitivity of the measurement
system and containing the calibration sound
pressure level.
A36.3.1.11
Calibration
check
frequency
means, in hertz, the nominal frequency of
the sinusoidal sound pressure signal produced by the sound calibrator.
A36.3.1.12 Level difference means, in decibels, for any nominal one-third octave
midband frequency, the output signal level
measured on any level range minus the level
of the corresponding electrical input signal.
A36.3.1.13 Reference level difference means,
in decibels, for a stated frequency, the level
difference measured on a level range for an
electrical input signal corresponding to the
calibration sound pressure level, adjusted as
appropriate, for the level range.
A36.3.1.14 Level non-linearity means, in decibels, the level difference measured on any
level range, at a stated one-third octave
nominal midband frequency, minus the corresponding reference level difference, all
input and output signals being relative to
the same reference quantity.

A36.3.1.15 Linear operating range means, in
decibels, for a stated level range and frequency, the range of levels of steady sinusoidal electrical signals applied to the input
of the entire measurement system, exclusive
of the microphone but including the microphone preamplifier and any other signal-conditioning elements that are considered to be
part of the microphone system, extending
from a lower to an upper boundary, over
which the level non-linearity is within specified tolerance limits.
NOTE: Microphone extension cables as configured in the field need not be included for
the linear operating range determination.
A36.3.1.16 Windscreen insertion loss means,
in decibels, at a stated nominal one-third octave midband frequency, and for a stated
sound incidence angle on the inserted microphone, the indicated sound pressure level
without the windscreen installed around the
microphone minus the sound pressure level
with the windscreen installed.
A36.3.2 Reference environmental conditions.
A36.3.2.1 The reference environmental conditions for specifying the performance of a
measurement system are:
(a) Air temperature 73.4 SectionF (23 SectionC);
(b) Static air pressure 101.325 kPa; and
(c) Relative humidity 50%.
A36.3.3. General.
NOTE: Measurements of aircraft noise that
are made using instruments that conform to
the specifications of this section will yield
one-third octave band sound pressure levels
as a function of time. These one-third octave
band levels are to be used for the calculation
of effective perceived noise level as described
in section A36.4.
A36.3.3.1 The measurement system must
consist of equipment approved by the FAA
and equivalent to the following:
(a) A windscreen (See A36.3.4.);
(b) A microphone system (See A36.3.5):
(c) A recording and reproducing system to
store the measured aircraft noise signals for
subsequent analysis (see A36.3.6);
(d) A one-third octave band analysis system (see A36.3.7); and
(e) Calibration systems to maintain the
acoustical sensitivity of the above systems
within specified tolerance limits (see
A36.3.8).
A36.3.3.2. For any component of the measurement system that converts an analog signal to digital form, such conversion must be
performed so that the levels of any possible
aliases or artifacts of the digitization process will be less than the upper boundary of
the linear operating range by at least 50 dB
at any frequency less than 12.5 kHz. The
sampling rate must be at least 28 kHz. An
anti-aliasing filter must be included before
the digitization process.
A36.3.4 Windscreen.

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