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Author Topic: DMX or Audio? how to ID unmarked cables?  (Read 18000 times)

dave moldover

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DMX or Audio? how to ID unmarked cables?
« on: April 03, 2012, 01:25:24 PM »

Trying to separate and ID many finished XLR cables we have from various sources. Some are marked "microphone" or "audio". Others are marked DMX so we assume high impedance digital signal cable.
What is the simplest, reliable way to determine the type of the unmarked cables? Once we get them all sorted out I'll mark them permanently so they won't get mixed up again.

thanks.
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James Feenstra

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Re: DMX or Audio? how to ID unmarked cables?
« Reply #1 on: April 04, 2012, 11:10:15 AM »

get an ohm meter....if the resistance of the cable is ~60ohms, it's not for dmx
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Mac Kerr

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Re: DMX or Audio? how to ID unmarked cables?
« Reply #2 on: April 04, 2012, 11:26:33 AM »

get an ohm meter....if the resistance of the cable is ~60ohms, it's not for dmx

How does that work? The characteristic impedance of DMX or digital audio cable is supposed to be 110Ω to 120Ω, but that is not resistance, which will be the same for either, based on wire gauge. The characteristic impedance is based on an infinite length of cable (no reflections) at the frequency in question, which is in the megahertz for DMX and digital audio.

Mac
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Nick Pignetti

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Re: DMX or Audio? how to ID unmarked cables?
« Reply #3 on: April 04, 2012, 01:10:53 PM »

I can't answer your specific questions regarding cables you already have, but what I do to keep it organized is this:

I buy bulk wire and roll my own.
DMX>Grey Cable
Audio>Black Cable

Then, I use color coded rings on the adapters to designate the length.
blue=15ft
red=25ft.
yellow=5ft.
etc. etc.
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Randall Hyde

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Re: DMX or Audio? how to ID unmarked cables?
« Reply #4 on: April 04, 2012, 03:19:37 PM »

Trying to separate and ID many finished XLR cables we have from various sources. Some are marked "microphone" or "audio". Others are marked DMX so we assume high impedance digital signal cable.
What is the simplest, reliable way to determine the type of the unmarked cables? Once we get them all sorted out I'll mark them permanently so they won't get mixed up again.

thanks.

Can't help you with unmarked cables in a bin.  I always stick red (audio) or green (DMX) shrink-wrap on the XLR connectors to identify the cables (also identifies them as *mine* at a venue, as I've never met anyone else who does this). Also, on my audio cables, I tie a quick knot in the cable next to the XLR connector and put the shrink-wrap over that (and on to the connector) to provide extra strain relief.

If I couldn't figure out a cable's type, it would likely become a DMX cable - mic cables seem to work better as DMX cables than DMX cables work as audio cables.
Cheers,
Randy Hyde
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Mac Kerr

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Re: DMX or Audio? how to ID unmarked cables?
« Reply #5 on: April 04, 2012, 05:14:05 PM »

If I couldn't figure out a cable's type, it would likely become a DMX cable - mic cables seem to work better as DMX cables than DMX cables work as audio cables.
Cheers,
Randy Hyde

DMX cables should work just fine as audio cables, audio cables may not work as DMX cables. Audio will be fine over any kind of twisted pair, DMX has very specific needs.

Mac
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Randall Hyde

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Re: DMX or Audio? how to ID unmarked cables?
« Reply #6 on: April 04, 2012, 07:41:31 PM »

DMX cables should work just fine as audio cables, audio cables may not work as DMX cables. Audio will be fine over any kind of twisted pair, DMX has very specific needs.

Mac

Good to know.
Though I've often used mic cables as DMX cables in a pinch. Never had any problems. Of course, I always use terminators, too.

I have used DMX for audio, but only for line level. Though I've long since purchased enough audio cables that I'd never find myself short, I'll have to keep this in mind if the unthinkable does occur and I have a mic and a DMX cable and that's it.
Cheers,
Randy Hyde
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James Feenstra

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Re: DMX or Audio? how to ID unmarked cables?
« Reply #7 on: April 05, 2012, 10:16:36 PM »

How does that work? The characteristic impedance of DMX or digital audio cable is supposed to be 110Ω to 120Ω, but that is not resistance, which will be the same for either, based on wire gauge. The characteristic impedance is based on an infinite length of cable (no reflections) at the frequency in question, which is in the megahertz for DMX and digital audio.

Mac
You can still measure the impedance of the cable with a quality meter...

Another way would involve reading what's printed on the cable (model number) and sticking it into google...95% of the time you'll get some kind of conclusive result
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Elevation Audiovisual
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Mac Kerr

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Re: DMX or Audio? how to ID unmarked cables?
« Reply #8 on: April 05, 2012, 10:22:18 PM »

You can still measure the impedance of the cable with a quality meter...

So what is the impedance of a 25' piece of cable? How about a 1000' piece? Which one is 110Ω?

Mac
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duane massey

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Re: DMX or Audio? how to ID unmarked cables?
« Reply #9 on: April 05, 2012, 11:50:25 PM »

Rarely had a problem using audio cable for DMX, never had a problem using DMX cable for audio (other than having to cut off two of the 5 pins and bending the other ones and filing them down...).
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Duane Massey
Technician, musician, stubborn old guy
Houston, Texas

ProSoundWeb Community

Re: DMX or Audio? how to ID unmarked cables?
« Reply #9 on: April 05, 2012, 11:50:25 PM »


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