921
Federal Aviation Administration, DOT
Pt. 36, App. A
are representative of those conditions exist-
ing over the geographical area in which noise
measurements are made.
A36.2.3
Flight path measurement.
A36.2.3.1 The airplane height and lateral
position relative to the flight track must be
determined by a method independent of nor-
mal flight instrumentation such as radar
tracking, theodolite triangulation, or photo-
graphic scaling techniques, to be approved
by the FAA.
A36.2.3.2 The airplane position along the
flight path must be related to the noise re-
corded at the noise measurement locations
by means of synchronizing signals over a dis-
tance sufficient to assure adequate data dur-
ing the period that the noise is within 10 dB
of the maximum value of PNLT.
A36.2.3.3 Position and performance data re-
quired to make the adjustments referred to
in section A36.9 of this appendix must be
automatically recorded at an approved sam-
pling rate. Measuring equipment must be ap-
proved by the FAA.
Section A36.3 Measurement of Airplane Noise
Received on the Ground
A36.3.1
Definitions.
For the purposes of section A36.3 the fol-
lowing definitions apply:
A36.3.1.1
Measurement system means the
combination of instruments used for the
measurement of sound pressure levels, in-
cluding a sound calibrator, windscreen,
microphone system, signal recording and
conditioning devices, and one-third octave
band analysis system.
N
OTE
: Practical installations may include
a number of microphone systems, the out-
puts from which are recorded simultaneously
by a multi-channel recording/analysis device
via signal conditioners, as appropriate. For
the purpose of this section, each complete
measurement channel is considered to be a
measurement system to which the require-
ments apply accordingly.
A36.3.1.2
Microphone system means the com-
ponents of the measurement system which
produce an electrical output signal in re-
sponse to a sound pressure input signal, and
which generally include a microphone, a pre-
amplifier, extension cables, and other de-
vices as necessary.
A36.3.1.3
Sound incidence angle means in de-
grees, an angle between the principal axis of
the microphone, as defined in IEC 61094–3 and
IEC 61094–4, as amended and a line from the
sound source to the center of the diaphragm
of the microphone.
N
OTE
: When the sound incidence angle is
0
°
, the sound is said to be received at the
microphone at ‘‘normal (perpendicular) inci-
dence;’’ when the sound incidence angle is
90
°
, the sound is said to be received at ‘‘graz-
ing incidence.’’
A36.3.1.4
Reference direction means, in de-
grees, the direction of sound incidence speci-
fied by the manufacturer of the microphone,
relative to a sound incidence angle of 0
°
, for
which the free-field sensitivity level of the
microphone system is within specified toler-
ance limits.
A36.3.1.5
Free-field sensitivity of a micro-
phone system means, in volts per Pascal, for
a sinusoidal plane progressive sound wave of
specified frequency, at a specified sound inci-
dence angle, the quotient of the root mean
square voltage at the output of a microphone
system and the root mean square sound pres-
sure that would exist at the position of the
microphone in its absence.
A36.3.1.6
Free-field sensitivity level of a micro-
phone system means, in decibels, twenty
times the logarithm to the base ten of the
ratio of the free-field sensitivity of a micro-
phone system and the reference sensitivity
of one volt per Pascal.
N
OTE
: The free-field sensitivity level of a
microphone system may be determined by
subtracting the sound pressure level (in deci-
bels re 20
μ
Pa) of the sound incident on the
microphone from the voltage level (in deci-
bels 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 loga-
rithm 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
μ
Pa.
A36.3.1.8
Level range means, in decibels, an
operating range determined by the setting of
the controls that are provided in a measure-
ment system for the recording and one-third
octave band analysis of a sound pressure sig-
nal. 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 deter-
mine 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 pro-
duced by the sound calibrator.
A36.3.1.12
Level difference means, in deci-
bels, 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.
VerDate Mar<15>2010
10:12 Mar 18, 2014
Jkt 232046
PO 00000
Frm 00931
Fmt 8010
Sfmt 8002
Y:\SGML\232046.XXX
232046
pmangrum on DSK3VPTVN1PROD with CFR