SC-226 MEETING MINUTES Working Group JANUARY 14 ... - RTCA

RTCA Paper No. 021-13/SC226-010
February 6, 2013
3.2.2Acoustic Output
The acoustic output of the headset should be 100 dB, ref. 0.0002 dynes per square centimeter per 1.0
milliwatt (0.5 mW per earphone) in the frequency range of 300 to 4000 Hz within the following limits:
300 Hz ± 3 dB ref. 100 dB per 0.5 mW
1000 Hz ± 1.5 dB
4000 Hz ± 3 dB
8000 Hz ± 10 dB or more
Note: 100 dB per 0.5 mW is equivalent to 20 dynes per square
centimeter per 0.5 mW, or 52 dynes per square cenitmeter
per 1 volt.
COMMENTARY
The headset acoustic output should not exceed 100 dB per
milliwatt because a desired signal-to-noise ratio of 46 dB requires
that the system noise hum level be suppressed to a value below 4
millivolts.
Discussion of headset connectors. The committee discussed the benefits of the XLR-5 versus the XLR-7
connector. The problem with XLR-5 is that it has too few pins to include DC-. As a result, DC – is often
shared with the MIC return causing conducted audio frequency (400 Hz commonly) noise problems in
the ANR headset audio.
XLR-7 provides additional pins, not only for DC – but also includes a pin that can be used for headset
stereo right. Headset stereo left can be dual use with headset mono HI.
The Sennheiser white paper submitted at the July 2012 SC226 DO-214 committee meeting was
referenced. The following language is proposed for the standard.
3.3Plug (from ARINC535B draft)
A single plug and cord should be provided for the microphone and headset. The plug should be an XLR-
7 straight plug with the following pin connections:
Pin 1 – Headset Hi/Left
Pin 2 – Headset Lo
Pin 3 – Mic pre-amp Hi
Pin 4 – Mic pre-amp Lo
Pin 5 - DC+
Pin 6 - DC-
Pin 7 - Headset Hi/Right
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