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Author Topic: A Silly Question???  (Read 3108 times)

Tony Martin

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A Silly Question???
« on: November 13, 2007, 10:14:11 am »

Someone told me recently that using mic cables to carry DMX signal "burns out" the mic lines, eventually making them useless.
Now I have read that it is better to use dedicated DMX cables, but that mic lines are acceptable.
Personally, I do not believe that DMX signal carries enough current to damage a mic line, but hey, I've been wrong before!!!
Any truth to this???
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Dan Brown

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Re: A Silly Question???
« Reply #1 on: November 13, 2007, 11:14:58 am »

Tony Martin wrote on Tue, 13 November 2007 09:14

Someone told me recently that using mic cables to carry DMX signal "burns out" the mic lines, eventually making them useless.
Now I have read that it is better to use dedicated DMX cables, but that mic lines are acceptable.
Personally, I do not believe that DMX signal carries enough current to damage a mic line, but hey, I've been wrong before!!!
Any truth to this???


NO

db
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Eric Hassler

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Re: A Silly Question???
« Reply #2 on: November 13, 2007, 11:31:29 am »

 Laughing no   Smile
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Karl P(eterson)

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Re: A Silly Question???
« Reply #3 on: November 13, 2007, 12:30:58 pm »

But there _IS_ some truth to this under certain conditions involving long lines and the microplex or its other protocol variants.

Many of the small microplex consoles get power from the dimmer pack, if it is one of the bigger signal line powered consoles and the line is long, it can melt mic cable's jackets and short out.

This of course doesn't have anything to do with DMX where you shouldn't use mic cable for signal lines, but not because it will hurt the cable.

Karl P

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Tony Martin

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Re: A Silly Question???
« Reply #4 on: November 14, 2007, 09:52:44 am »

I thought it sounded like a load of horse droppings.
Part of my suspicion was that the original info came from a salesperson. Methinks he was trying to make some extra commission by selling some DMX cabling.
Thanks for the info, folks.
Oh yes, and Karl, my DMX console has its own power supply, so no worries there.
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Karl P(eterson)

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Re: A Silly Question???
« Reply #5 on: November 14, 2007, 10:54:21 am »

Well, you certainly _should_ _not_ run DMX over mic lines, but it won't damage the mic line.

Your fixtures may not work right, but your cable will be safe Smile.

You should use DMX cable, or Cat5 cable at very least.

Karl P
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Dan Brandesky

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Re: A Silly Question???
« Reply #6 on: December 01, 2007, 10:13:33 pm »

FWIW...at the theatre at the college I attend, we regularly move the lighting console to the stage for smaller events between shows, and there is no DMX input for the console there (which is ironic because the dimmers are about 5 feet away from there). So we connect the board through the house snake to the booth, then connect that snake channel in the booth back to the console input up there, which goes back to the dimmer racks. We have never had a problem, and we have ~190 or so dimmer channels...

-Dan
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Owen Davis

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Re: A Silly Question???
« Reply #7 on: December 02, 2007, 02:16:37 am »

Once again, there is the "right way", and there is the "get by making it work on a budget way".

The "right way" - which in this case is using proper DMX cabling - is the right way for a reason.  You will have less problems, you will be able to rely on your rig working like it's supposed to, and you won't be wasting money in the long run on temporary solutions.  If you can afford it, get the proper cables.

However, the "get by....budget way" does have it's place.  You will not damage the cables at all by running mic cables.  Most likely (and that's the crux - most likely, but no guarantee) if you are running relatively short lines and few fixtures you will get by just fine with mic cables (especially good twisted pair ones).  

On the for-what-its-worth front: I run upwards of 46 fixtures, with a total of about 180-200 feet of cabling and I use mic cables.  This rig has seen a LOT of use in a lot of different venues, and I've never had any problems (at least none that were cable related).  I didn't plan to do it this way.  My rig has grown bit by bit, and when it started I had mic cables available so I used them, telling myself that I would switch to "proper" DMX cabling in the future.  It always seemed that whenever I added a new fixture or two, I had a mic cable handy and opted to use that "just for now" rather than buy something new.  So after a while I found myself running a somewhat extensive rig, all with the "wrong" cables.  BUT....it's all working so the incentive to go out and spend a big chunk of change to fix something that ain't broke is not exactly strong.  

So, don't mickey-mouse it if you can afford not to.  But don't completely discount the concept either.  

One thing though...DO absolutely use a terminator at the end of your line.  This will make a much bigger difference to the performance of your system than using proper cabling.  
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Duncan Macmillan

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Re: A Silly Question???
« Reply #8 on: February 11, 2008, 01:42:17 pm »

Hi all,
just reading this and as I understand it, the difference in the cable (audio xlr vs DMX/cat5) is its capacitance.  Audio signal cable displays high capacitance compared to low capacitance data cable.  The implication being that the data forms send through the cable react differently.  

For sake of argument think of audio signal as strictly a sine wave and digital data as strictly a square wave.  Capacitors (the electronic part) and the measure of capacitance is simply something which takes a charge and dissipates it over a longer period of time. Charges very quickly and releases that charge relatively very slowly.

Analog audio signals are generally (baring the undesirable square wave) curved sine wave and react negligibly to higher capacitance in the cable, ie if the peaks of said sine wave slope slower due to higher capacitance the signal is degraded, but relatively unnoticeable.  

However digital data being on's and off's, 1/0's, highs/lows, react poorly to the high capacitance of audio cable.  So, if you put DMX through an audio signal cable, the peaks (digital on value) being square shaped will end up distorted and cause an undesirable slope on the back side of the peaks in the information steam.  

I hope I'm making sense to you.  I thought this would be easier to explain.  All that being said, audio xlr is cheaper and widely used.  The advice given here is good, terminate your ends to eliminate data feedback and 9 times out of 10 you'll be fine.
All the best,
-Duncan
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