Pt. 36, App. A

14 CFR Ch. I (1-1-19 Edition)

spaschal on DSK3GDR082PROD with CFR

A36.3.4.1 In the absence of wind and for sinusoidal sounds at grazing incidence, the insertion loss caused by the windscreen of a
stated type installed around the microphone
must not exceed Section1.5 dB at nominal one-third
octave midband frequencies from 50 Hz to 10
kHz inclusive.
A36.3.5 Microphone system.
A36.3.5.1 The microphone system must
meet the specifications in sections A36.3.5.2
to A36.3.5.4. Various microphone systems
may be approved by the FAA on the basis of
demonstrated
equivalent
overall
electroacoustical performance. Where two or
more microphone systems of the same type
are used, demonstration that at least one
system conforms to the specifications in full
is sufficient to demonstrate conformance.
NOTE: An applicant must still calibrate
and check each system as required in section
A36.3.9.
A36.3.5.2 The microphone must be mounted
with the sensing element 4 ft (1.2 m) above
the local ground surface and must be oriented for grazing incidence, i.e., with the
sensing element substantially in the plane
defined by the predicted reference flight path
of the aircraft and the measuring station.

The microphone mounting arrangement
must minimize the interference of the supports with the sound to be measured. Figure
A36-1 illustrates sound incidence angles on a
microphone.
A36.3.5.3 The free-field sensitivity level of
the microphone and preamplifier in the reference direction, at frequencies over at least
the range of one-third-octave nominal
midband frequencies from 50 Hz to 5 kHz inclusive, must be within Section1.0 dB of that at the
calibration check frequency, and within Section2.0
dB for nominal midband frequencies of 6.3
kHz, 8 kHz and 10 kHz.
A36.3.5.4 For sinusoidal sound waves at
each one-third octave nominal midband frequency over the range from 50 Hz to 10 kHz
inclusive, the free-field sensitivity levels of
the microphone system at sound incidence
angles of 30Section, 60Section, 90Section, 120Section and 150Section, must not
differ from the free-field sensitivity level at
a sound incidence angle of 0Section ( - normal incidence - ) by more than the values shown in
Table A36-1. The free-field sensitivity level
differences at sound incidence angles between any two adjacent sound incidence angles in Table A36-1 must not exceed the tolerance limit for the greater angle.

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