Obscure techie question......sorry!

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Russ Gannicott
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Joined: Thu Apr 26, 2007 8:28 pm

Obscure techie question......sorry!

Postby Russ Gannicott » Mon Sep 01, 2008 6:25 pm

OK..here we go; does anyone have any idea if it is acceptable to transmit DMX data down the same multi core that you are using for audio from stage box to mixer? DMX cables are two core screened and XLR mic cables work fine. The only question would be cross-talk. Any thoughts?
Cheers!

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Steve Smith
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Joined: Sat Apr 21, 2007 11:03 pm
Location: Somerset Uk

DMX on Audio Multicore

Postby Steve Smith » Wed Oct 01, 2008 10:50 pm

Hi Russ,

I've never tried this but my instincts (along with being an electronics engineer) tell me that it probably wouldn't be a good idea.

The DMX Wiki http://en.wikipedia.org/wiki/DMX512-A has this to say:

"Cabling for DMX512 was removed from the standard and a separate cabling standards project was started in 2004.
Two cabling standards have been developed, one for portable DMX512 cables and one for permanent installations. This resolved previous issues arising from the differing needs of cables used in touring shows versus cables used for permanent infrastructure.
In addition, cable performance is now specified with regard to nominal impedance and capacitance to provide guidance as to what constitutes an acceptable cable.
For example, microphone and line level audio cables do not have the correct characteristics and should never be used for DMX512. The significantly lower nominal impedance and significantly higher capacitance of these cables distort the DMX512 data which can cause irregular operation or intermittent errors that are difficult to identify and correct."

Actually, my concerns were more to do with bleed of the 250kHz RS485 signals into the audio signals, and safety concerns as the lighting controllers may be on different phases of the mains supply from the audio systems

So I guess that's a 'No', then :(

Steve Smith

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Russ Gannicott
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Joined: Thu Apr 26, 2007 8:28 pm

Postby Russ Gannicott » Sat Oct 04, 2008 9:22 pm

Thanks Steve,
These were mostly my concerns also. However, despite what the Wiki article says I have never had any problem sending DMX down two core screened mic cables and recently did so along a 50m length without any trouble. I think I'll stick to using the extra cable and not run risks with the multi-core idea. Thanks for your input.
All the best,
Russ


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