# The Ongoing Debate of Mic Cable for DMX



## bishopthomas (Feb 19, 2012)

So I modified my MagicQ dongle for use with 3 or 5 pin connectors (see pictures below) and added some expandable nylon sleeving and noticed that the cable used was microphone cable. I forgot to snap a shot before putting the sleeving on, but it obviously said microphone cable right on it. How do you purists feel about a company such as Chamsys using microphone cable instead of "proper" DMX data cable? Personally, I don't have a problem with it. Until recently I was using strictly mic cable for all of my cable runs. I have been making new cable and switching over to DMX but only "just because;" I've never had any problems due to using microphone cable. All of my 3 to 5 pin adapters use Gepco install mic cable with expandable sleeving over it, again never any problems. But I know there are some of you out there who are very much against using mic cable to connect lighting gear, so please discuss.


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## mstaylor (Feb 19, 2012)

It is sad that a company that should know etter is using noncompliant cable. That said, it is a very short piece so it shouldn't affect anything. Where you get into problems is on lengths of cable, which is why we always suggest no using it. Again, 3 to 5 adapters are short pieces and shouldn't be a problem.


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## bishopthomas (Feb 19, 2012)

mstaylor said:


> That said, it is a very short piece so it shouldn't affect anything.



I'm guessing that's what the blokes at Chamsys decided as well.


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## Wood4321 (Feb 19, 2012)

mstaylor said:


> It is sad that a company that should know etter is using noncompliant cable. That said, it is a very short piece so it shouldn't affect anything. Where you get into problems is on lengths of cable, which is why we always suggest no using it. Again, 3 to 5 adapters are short pieces and shouldn't be a problem.



I agree 100%
The problem with dmx is that I will put up with alot, right up to the point when the whole house of cards comes tumbling down.
This usually happens 5 minutes after doors, or at places...
However the first rental company that sends me mic cable with a rental is going to not get anymore of my business.
Of course in this case we are talking about a short cable, not a 100' snake. I would be surprised if the adapter caused an issue.


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## bishopthomas (Feb 19, 2012)

Woodj32177 said:


> I agree 100%
> The problem with dmx is that I will put up with alot, right up to the point when the whole house of cards comes tumbling down.
> This usually happens 5 minutes after doors, or at places...
> However the first rental company that sends me mic cable with a rental is going to not get anymore of my business.
> Of course in this case we are talking about a short cable, not a 100' snake. I would be surprised if the adapter caused an issue.



I find this die hard mentality contradictory. You would go so far as to never use a rental house again if they send you a mic cable but you say it's alright in short runs. You can't have it both ways. It's either acceptable or it's not. For the record, I have sent DMX down a very many audio snakes and never had a problem. I now tend to refrain, opting for wireless DMX instead. But if I had to I certainly wouldn't be upset about it.


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## MNicolai (Feb 19, 2012)

bishopthomas said:


> I find this die hard mentality contradictory. You would go so far as to never use a rental house again if they send you a mic cable but you say it's alright in short runs. You can't have it both ways. It's either acceptable or it's not. For the record, I have sent DMX down a very many audio snakes and never had a problem. I now tend to refrain, opting for wireless DMX instead. But if I had to I certainly wouldn't be upset about it.



Correct me if I am wrong, but the characteristics that make or break a DMX data cable (nominal capacitance and nominal resistance) are distance-related. The metric for those characteristics is generally compared against infinitely long piece of cable, but could also be measured for a given length of cable.

I'm not smart enough about DMX to make a conclusion one way or the other, but from what I do know about DMX cables and the ideal characteristics of them, I would not be surprised if a short piece of cable has negligible impact on the function of a system.

Maybe JFleenor can comment on whether the length of cable matters?


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## mstaylor (Feb 19, 2012)

bishopthomas said:


> I find this die hard mentality contradictory. You would go so far as to never use a rental house again if they send you a mic cable but you say it's alright in short runs. You can't have it both ways. It's either acceptable or it's not. For the record, I have sent DMX down a very many audio snakes and never had a problem. I now tend to refrain, opting for wireless DMX instead. But if I had to I certainly wouldn't be upset about it.


I work with a sporting system that produces weekly shows for TV. They also do nontelevised regularly and on the nontelevised shows they run their DMX through their house snake. Exactly what Josh said did happen. Everything was beautiful until the house opened and the DMX went nuts. My first question when I looked at it was," You are going through the house snake?" He said he always did. Then I asked how much DMX cable did he have? No idea there was a difference. I pulled my cable out and ran it across the floor. 
The fact is you can do it thousands of times and it will be fine, then one night it will go south. Wireless DMX is not all that dissimilar, just different headaches.


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## bishopthomas (Feb 19, 2012)

I'm with you, Mike. I'm sure distance is a factor but am unsure at what point that distance becomes a liability. The reason I bring this discussion up is because of the mentality of Joshua. He seems so adamantly against using mic cable, why not make it a policy to actually uphold? If it's okay to use for adapters why isn't it okay to use in short runs to fixtures? Where is the line to be drawn? A four inch adapter is okay, but an 18" cable is not? Obviously the difference is more clear if all of your cable runs are 30', but why make a distinction because of distance?


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## bishopthomas (Feb 19, 2012)

mstaylor said:


> The fact is you can do it thousands of times and it will be fine, then one night it will go south. Wireless DMX is not all that dissimilar, just different headaches.



I hear you loud and clear, and this is the reason why I'm switching over to purely DMX cable. Please don't misunderstand me as saying that using mic cable is acceptable, I'm just trying to bring up a point that some people are very staunch in their opinions but why is it okay to vary that opinion when a detail such as length is introduced?

Also, I've never had a single issue with wireless DMX and don't at all equate it with running microphone cable. I also know several companies that use it for every show, every day, and have also had no issues. I'm talking about high quality wireless with FHSS capability, not the low budget fixed channel variety.


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## mstaylor (Feb 19, 2012)

bishopthomas said:


> I'm with you, Mike. I'm sure distance is a factor but am unsure at what point that distance becomes a liability. The reason I bring this discussion up is because of the mentality of Joshua. He seems so adamantly against using mic cable, why not make it a policy to actually uphold? If it's okay to use for adapters why isn't it okay to use in short runs to fixtures? Where is the line to be drawn? A four inch adapter is okay, but an 18" cable is not? Obviously the difference is more clear if all of your cable runs are 30', but why make a distinction because of distance?


First Joshua builds shows all over the place, I believe he has been to my building. A twenty foot cable probably isn't a problem but you add four or five together and they are a problem. When I order movers, LEDs or anything else that requires DMX, I expect DMX compliant cable. 
Think of it this way. I order 10 S4 PARs and cable to run them. 14 will carry it but I would expect 12 to be sent so I could run whatever lengths I want. 14 would limit my options. Mic cable vs DMX is the same, very short pieces aren't a problem, added together they are a problem.


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## bishopthomas (Feb 19, 2012)

mstaylor said:


> First Joshua builds shows all over the place, I believe he has been to my building.



Okay... I'm not attacking him, only questioning his methods and practices. I'm not posing these questions to argue, only to cause some thought to go into the answers.


mstaylor said:


> A twenty foot cable probably isn't a problem but you add four or five together and they are a problem. When I order movers, LEDs or anything else that requires DMX, I expect DMX compliant cable.
> Think of it this way. I order 10 S4 PARs and cable to run them. 14 will carry it but I would expect 12 to be sent so I could run whatever lengths I want. 14 would limit my options. Mic cable vs DMX is the same, very short pieces aren't a problem, added together they are a problem.



Again, I totally agree. But why stick a piece of mic cable into a rig that otherwise has none in it? And you would automatically dismiss a company that sends mic cable rather than talk to them about it? If everything else is completely satisfactory, rather than specifically request DMX cable next time (or a replacement) you would just not call them again?


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## derekleffew (Feb 19, 2012)

MNicolai said:


> ...Maybe JFleenor can comment on whether the length of cable matters?



Informational Video: DMX512 Cable - Part One - YouTube
Fast forward to 2:35 for Mic cable for DMX transmission.


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## mstaylor (Feb 19, 2012)

bishopthomas said:


> Okay... I'm not attacking him, only questioning his methods and practices. I'm not posing these questions to argue, only to cause some thought to go into the answers.
> 
> 
> 
> Again, I totally agree. But why stick a piece of mic cable into a rig that otherwise has none in it? And you would automatically dismiss a company that sends mic cable rather than talk to them about it? If everything else is completely satisfactory, rather than specifically request DMX cable next time (or a replacement) you would just not call them again?


My point that because he works in many venues in many parts of the country he wants the components be the correct type. Enough things can go wrong on a gig, having the wrong cable because it usually works is not a headache he wishes to have. Unfortunately I have to work with what others have ordered or brought. In your case, I think you are setting up your gear for your contracts, so you deal with your headaches. If you are shipping gear to somebody else, they should get what they ask for. 
In an area like I live in, I don't have to option to kick a company to the curb like Josh can. Most movers are two hours away, the next is another hour. If they were sending me cables that "could" take my show down, I wouldn't be happy. I would either insist a correction the next time, a reduction on this time or I would buy my own cable.


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## bishopthomas (Feb 19, 2012)

Dr. DMX! Where do you find this stuff!?


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## bishopthomas (Feb 20, 2012)

So, any other opinions about this topic? Anyone have real data to back it up? O-scope readings? Who has had issues with improper cabling that could be confirmed to be a cabling issue?


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## JD (Feb 20, 2012)

bishopthomas said:


> So, any other opinions about this topic? Anyone have real data to back it up? O-scope readings? Who has had issues with improper cabling that could be confirmed to be a cabling issue?



About the only thing that comes to mind is that (some) microphone cable is a little better and handling continuous hard twisting and flexing due to it's lack of a full shield. (Usually a braided weave.) Could be that in building the adapter, that compromise was made based on that characteristic.


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## Wood4321 (Feb 20, 2012)

mstaylor said:


> My point that because he works in many venues in many parts of the country he wants the components be the correct type. Enough things can go wrong on a gig, having the wrong cable because it usually works is not a headache he wishes to have. Unfortunately I have to work with what others have ordered or brought. In your case, I think you are setting up your gear for your contracts, so you deal with your headaches. If you are shipping gear to somebody else, they should get what they ask for.
> In an area like I live in, I don't have to option to kick a company to the curb like Josh can. Most movers are two hours away, the next is another hour. If they were sending me cables that "could" take my show down, I wouldn't be happy. I would either insist a correction the next time, a reduction on this time or I would buy my own cable.



Michael, 
You are 100% correct.
I have had the misfortune of having 1 bad piece of data cable take down an entire rig. (I didn't design that system)
Therefore I make it my policy to use the correct cable for everything. 
Just to be clear, I never allow audio cable in my DMX runs.
However, I don't think a short adapter will cause a problem, as long as your cable run is short. 

As for rental companies, If I was in Michael's shoes I likely would do the same, but I have at least 3 or 4 companies I can choose to do business with. So I do have a lot more choice in the matter.


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## AEGProduction (Feb 20, 2012)

One thing I would like to add. In transmission lines, if the impedance is not the same from the beginning of the line, through each of the "splits" (Each light), and at the end (terminator or last light), power loss (signal loss in dB) can occur. This was an issue in RF lines (cable TV and such) however it can apply here as well. The mismatched impedance will cause reflections which can cause errors (usually this is what a terminator is for, however having the line terminated at 110 ohms, when using a different impedance cable can cause even more loss) 

That being said, my only thought on using a short mic cable with a long cable is that you will have a mismatched impedance on the beginning line reducing the signal power. HOWEVER, I do no think this cause an issue, as long as the rest of the rig is the same.

A horror story of mine that I have using mic vs. DMX, one that I hope will hit home with everyone. This was my first big show I had ever booked. I did not own DMX cable, the shop I rented the majority of the lights from did not own DMX cable (why?), but because I originally wanted to be a live sound engineer, I had miles of mic cable that the shop said was fine to use. Here is the story:

I was to set up a new years show, (20 LED PARS for stage wash for a band, 4 moving heads with 8 Scanners around the dance area hung on upright truss sticks uplit with LED's, and 60 LED uplights around the room). We put up the stage wash powered and wired for DMX, I tested it beforehand, everything was ok so we cranked it up so the sound guys could start working. We erected the other truss uprights with the heads and scanner, tested fine, so we left them. Then the large quantity of uplights we used got placed throughout the room to dress the walls of the space. Everything tested fine individually with my console driving each line separately to test. (We had 2 1x4 Opto-Splitters which ran the splits for each leg of 20 or so lights). After we had connected and tested each branch individually, it was time to do the whole system. Plugged my console into the splitter, and went to go see some of my programs work! what the &%#$..............

I had no control over either branch of uplights, Half the stage lights would respond to my programs, and the other would do something completely different (as if I had them addressed incorrectly however they were fine as I had tested them individually). Good news though...my movers and scanners were working..... After I had suspected a bad cable from the front end of either chain of LED's I had my crew replace that cable with a known working one...nothing. I started to unplug the last fixtures in the chain, hoping it was a bad fixture or cable causing some weird issue....nothing. I did the same for the other branch of uplights...nothing. As I knew the branches worked individually I removed a branch of uplights from the splitter and hooked it up directly to the console. VOILA!! now what is the problem? After plugging it back into the splitter....nothing. I thought my splitter was fried. That was not the case. I called up a good friend of mine who I knew wasn't busy on new years eve. I told him my problem and he was clueless as well. He came through to the event and started to help me diagnose what could be wrong. We went through every thought and still couldn't figure out what was up. He then asked me, "You're using DMX cable right?" I said, "no mic cable works fine". He was stumped, but he brought out his trunk of DMX he had in his van. We replaced the first cable in the line from the splitter. BAM! I had control. We later replaced as much of the mic cable as we could with DMX before people started to file in. After about multiple hours of headaches and confusion, we had everything in the room working as it should. 

Later we tested the mic cable out at the shop, and we found that using the splitter, only some of the mic cable would pass signal, and some wouldn't (hence why the movers and scanners worked but nothing else did). It was impossible to tell which cable was going to work, and which wouldn't. He had never seen anything like this, and neither have I, nor do I ever want to go through that series of problems again, I was drenched in sweat from running around, the client thought I was on drugs because my answers when he asked, "Is everything good?" I replied,"Well I think maybe I don't know, refund, no show maybe I think hold on let me check....". ALL BECAUSE OF MIC CABLE.

So I decided to get the right cable for next time. Since then I have had 0! yes 0! issues with lights not acting as they should because of cabling. In my most humble opinion, using only DMX cable has proved to save me time, effort, and clients because I have one less thing to go wrong (unless you count each cable as 1 thing, then I have about 80 less things that could go wrong).

If a rental company gives me mic cable, I ask for DMX. If they do not have any, I usually try and source it elsewhere or buy it myself if I have to. If those are not an option...pray to the gods of theater and hope things go as they should?


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## gcpsoundlight (Feb 20, 2012)

Make sure to check it is actually DMX cable tho. I saw (at a local hire company) a box of packages "DMX" cables. Closer looking at the cables revealed that it was just mic cable as well. I would try to buy brand name stuff, I have seen to many instances of cheap cable not being what it says it is. 


Sent from my iDevice using Tapatalk - now you have to guess which one!


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## bishopthomas (Feb 20, 2012)

Hey, there, AEG. Thanks for the story, and more importantly, welcome to Control Booth! Good to see your organization represented here. It's funny that so many people have these horror stories and yet no one ever knows the Why of it all. The mic cable goblins are going to eat your babies! Did you ever ask your parents "Why not?" when they told you not to do something and get the response, "Because I said so?" They were always right, but WHY were they always right?


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## Wood4321 (Feb 20, 2012)

http://www.dfd.com/whyterm.html

This article is a good start, although it deals mostly with termination. (another bag of worms I suspect)


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## DavidNorth (Feb 20, 2012)

bishopthomas said:


> It's funny that so many people have these horror stories and yet no one ever knows the Why of it all. The mic cable goblins are going to eat your babies!



Well, actually a number of people do know why. Quite simply, it's capacitance. The more capacitive your cable path, the more slewing in the transitions between low and high bits. If there is enough slewing, the receiver chip now sees the transition time at a different time and then the data is no longer recognizable as DMX by the UART.

If you have high quality audio cable, the capacitance will be less. Low quality and the capacitance is typically more. Since audio frequencies are a lot lower than DMX and almost never have the sharp transitions in signal that DMX has, the higher level of capacitance (as compared to DMX cable) does not affect the audio signal. I do have scope shots but unfortunately they are at work and I'm not.

I can't begin to tell you how many times I've had people call in with control issues to find out they used mic cable. Every once in a while they say they checked all out in the shop before they brought it out on site. I then ask if the shop mock up used all the cable being used in the rig and the answer is always no.

The longer the mic cable run with DMX in it, the greater the possibility of loss of control.

David


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## bishopthomas (Feb 20, 2012)

DavidNorth said:


> Well, actually a number of people do know why. Quite simply, it's capacitance.



You're right, I misspoke. There are certainly people who do, in fact, know the why behind it all. It's just that that is never presented in the DON'T USE MIC CABLE! threads that I have seen. It's never questioned, just accepted as fact.

How do you feel about quad mic cable used for DMX? The capacitance is probably still too high, but is it approaching tolerable levels? And if so what is the relationship between DMX data cable, single twisted pair audio, and quad core audio cable?


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## DavidNorth (Feb 20, 2012)

bishopthomas said:


> How do you feel about quad mic cable used for DMX? The capacitance is probably still too high, but is it approaching tolerable levels? And if so what is the relationship between DMX data cable, single twisted pair audio, and quad core audio cable?



I'll be honest, as a long time proponent of using quality cable, I have never even researched quad mic cable. So, to give it a quick once over, I looked up the specs from Canare here: Canare Corp.: Star Quad Series: Star Quad Microphone cable(L-4E6S / L-4E5C). The typical DMX cable spec for capacitance is around 13pF/ft and the Canare quad is four times that. In addition, it has quite a low nominal impedance. 

There are a couple of factors that affect distance which include capacitance, cable impedance and the number of unit loads on the data chain. In an ideal world DMX can reach 1600'. I would guess that quad cable might get you 300' or so, but that is a complete guess. Cable runs are only going to get longer with the prevalence of LED fixtures and propensity to movers.

The more important question is: what is the loss of a show or the hours troubleshooting worth to you and does it cost anywhere near what a set of good quality DMX cables cost.

Using good quality DMX cable always works. Using mic cable might work. Beyond that, I leave it to you.


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## DavidNorth (Feb 20, 2012)

Oh funny, I just looked at the spec sheet I posted above and at the very bottom there is an interesting frequency chart for 100m (328ft). Yes, it shows a fall off to very low levels at frequencies just under the 250kHz mark. Now you can't exactly relate DMX bit rate (4uS) to a regular frequency, but no doubt the quad cable is not efficient at transmitting effective DMX data.


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## bishopthomas (Feb 20, 2012)

Thanks for your insight, David, very good stuff.


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## Chris15 (Feb 21, 2012)

DavidNorth said:


> Now you can't exactly relate DMX bit rate (4uS) to a regular frequency, but no doubt the quad cable is not efficient at transmitting effective DMX data.



But you can say that 1/(4us) equals 250kHz and get a rough approximation that way...
Which shows that at the sort of frequency we are talking about for DMX, Star Quad is amongst the least preferrable of all cables...


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## lampyken (Feb 21, 2012)

mstaylor said:


> It is sad that a company that should know etter is using noncompliant cable. That said, it is a very short piece so it shouldn't affect anything. Where you get into problems is on lengths of cable, which is why we always suggest no using it. Again, 3 to 5 adapters are short pieces and shouldn't be a problem.



I can assure that our Engineers understand transmission line theory very well - George has been working in the industry for over 30 years and was responsible for the electronics in many well known lighting products, including one of the Hog front panels and the Icon control desk - so he knows a bit electronics and DMX. We will use parts and techniques according to the particular product we are making - therefore when designing our professional range of consoles and DMX interfaces we would use more expensive parts then when we design a low cost device.

We sell the MagicDMX at £10 ($16) - that is how much it costs us to make it - we don't make a profit on it. The idea was to make a DMX device that was very low cost so that young people, students and people new to the industry could start off without spending much money. Even $16 is a lot of money in many parts of the world. MagicQ software is free to use and unlike our competitors all the universes are unlocked and can be used to output ArtNet/Pathport or ACN streaming DMX without purchasing anything.

By using standard 3 pin XLR cable pre-made we cut several $ off the price thus making it an even better bargain. 3 pin XLRs are much more common than 5pin XLR due to their usage in the audio and other industries.

It is interesting to note that the MagicDMX has been one of the most succesful products we have ever made in terms of reliability and customer feedback - we get very few complaints - it just works. Sometimes the simplest things in life are the best!

Chris Kennedy
Software Director
ChamSys


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## jpk (Feb 22, 2012)

Chris15 said:


> But you can say that 1/(4us) equals 250kHz and get a rough approximation that way...
> Which shows that at the sort of frequency we are talking about for DMX, Star Quad is amongst the least preferrable of all cables...


Actually it's far worse than that. Audio caps out around 20kHz sinusoidal waveform however DMX512 is 250kHz square wave (worst case) which means if you want a decent approximation of a square wave at the other end of your cable you'll be needing some higher order harmonics, for arguments sake up to 10x 250kHz. High capacitance cable needs more current from the RS485 driver and they simply current limit and round off the square wave to the point where on a long cable run it's pure hope the near sinewave DMX512 signal you've created will be squared up within the bit sampling tolerance of the receiving UART.

Worse still, and probably a good source of many failures, audio cables typically have the shield connected to both pin 1 and the connector case with can nullify your DMX isolator/splitter depending on it's design.


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## len (Feb 22, 2012)

I'll bet that most know that dmx cable is better for running dmx applications. And yet there have been times when, for whatever reason, we have been forced to use something else. Sometimes it was fine, and sometimes it wasn't. 

I can recall one episode where we DID use all dmx cable and still had an issue with one type of fixture. It took hours to rectify and to this day I still don't know why it happened. But if at all possible, I'm using dmx cable. 

As for termination, I don't do that too often (actually never) and it hasn't been an issue. But as I am fond of saying: whenever someone says "we've never had a problem" my standard response is "there's always a first time."


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## Wood4321 (Feb 22, 2012)

I agree.
I have had a terminator cause a chain of dmx fixtures fail.
However, the problem was not the terminator itself. There was a bad cable in the system that had pin 3 (IIRC) disconnected.
DMX will often work with one side disconnected, but in this case, the terminator caused the signal to drop too far for the fixtures to read.


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## TimMiller (Feb 23, 2012)

I have had the same type of failure using a terminator due to a bad cable (once it was a cold solder joint inside a fixture that caused the same problem. I learned once on a show dmx cable cannot be substituted for mic cable. It creates all sorts of weird buzzes. I have also seen companies sell dmx cable but when looking at the cable itself it is actually mic cable. Personally I wish 3pin dmx never existed. I have had to deal with lots of strange cable failures in clubs due to mic cable being used but I have not sat down and done any tests in the shop with a scope. It's on the thing to do list.


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## bishopthomas (Feb 23, 2012)

jpk said:


> ...audio cables typically have the shield connected to both pin 1 and the connector case...



Exactly 0 of my cables have pin one and chassis tied together. Mostly because I made the majority of them, but even the "over the counter" variety are separated. Most of my pre-made cables are from CBI.

But as for the rest of your post, great information, much appreciated.


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## bishopthomas (Feb 23, 2012)

On the flip side, however, DMX cable works just fine for microphones. I'm doing an audio gig on Sunday and will probably be using all DMX cable, only because it's more convenient at the moment. What is the difference in construction between the two varieties? The DMX cable I have just seems like twisted pair mic cable with a braided shield. I know there's something in there causing all that data goodness, but can't tell from the stripped 1/2" on the end.


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## jpk (Feb 23, 2012)

bishopthomas said:


> Exactly 0 of my cables have pin one and chassis tied together. Mostly because I made the majority of them, but even the "over the counter" variety are separated. Most of my pre-made cables are from CBI.
> 
> But as for the rest of your post, great information, much appreciated.



It's an interesting argument where EMC comes into play. Without pin 1 to shield you can't properly protect the data/audio pair from interference (ESD, RF, direct EM coupling...) since there's a discontinuity in the shielding. The E1.11 standard should address this but it doesn't at the moment however it is given consideration in audio standards AES Standard » AES48-2005 (r2010): AES standard on interconnections - Grounding and EMC practices - Shields of connectors in audio equipment containing active circuitry

The EMC vs Electrical Safety vs Practicality debate will go on forever. Personally I feel the addition of a small capacitor between pin 1 and connector chassis is probably a good compromise providing RF coupling without DC/LF problems.


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## jpk (Feb 23, 2012)

len said:


> I'll bet that most know that dmx cable is better for running dmx applications. And yet there have been times when, for whatever reason, we have been forced to use something else. Sometimes it was fine, and sometimes it wasn't.
> 
> I can recall one episode where we DID use all dmx cable and still had an issue with one type of fixture. It took hours to rectify and to this day I still don't know why it happened. But if at all possible, I'm using dmx cable.
> 
> As for termination, I don't do that too often (actually never) and it hasn't been an issue. But as I am fond of saying: whenever someone says "we've never had a problem" my standard response is "there's always a first time."



Think about a room with a really bad echo, that's what happens to your DMX512 signal when there's no termination. Signals hit the "open" end and reflect back again then mix with wanted signals potentially causing data corruption. OK with slow data rates like DMX512 this effect will only be an issue with long cable runs I'd never run a system without line termination.


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## DavidNorth (Feb 23, 2012)

bishopthomas said:


> On the flip side, however, DMX cable works just fine for microphones. I'm doing an audio gig on Sunday and will probably be using all DMX cable, only because it's more convenient at the moment. What is the difference in construction between the two varieties? The DMX cable I have just seems like twisted pair mic cable with a braided shield. I know there's something in there causing all that data goodness, but can't tell from the stripped 1/2" on the end.



Well, the insulation on the individual conductors will be both a different material, and in the case of the DMX cable, much thinner. Most of the time the DMX cable is also a smaller guage wire. It is the combination of thinner and different insulation, tighter twists per inch and smaller guage that defines the cable's capacitance and impedance. It may be hard to see the difference but it is indeed there. Don't forget that capacitance is defined as being two conducting plates [or conductors] seperated by a dielectric [insulation].

For comparison, look at the construction of a cable, CAT5E, which is designed for even higher data rates. The conductors are very small, tightly twisted and with a very thin insulation. What they couldn't solve in cable construction is handled by legally limiting usable distance to 100m.

Make sense?

David


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## gafftaper (Feb 24, 2012)

I want to take a second and right some things that were said in this thread. You can argue all you want about Mic Cable vs DMX Cable, whatever. However, no one should judge ChamSys as a company based on the build quality of a $16 product which is clearly not intended for any professional use. Their product page clearly says:

> The MagicDMX Basic interface is aimed at users wishing to evaluate and learn MagicQ, technicians wishing to test fixtures, as well as students wishing to learn lighting in schools and colleges.


 Further more the product FAQ adds:

> ...The MagicDMX is a very low cost interface designed to enable our users to evaluate MagicQ software with real lighting fixtures...


 This product is somewhere between a toy and a test tool, and is clearly not inteded to be relied upon in any way by professionals in a show situation. Therefore, complaining about build quality is extremely unfair to ChamSys. Anyone who's been around CB long knows how generous ChamSys is about giving away their software for free and the quality of their consoles has never been questioned in these forums. The fact that they give these dongles away at cost in part to help young technicians learn, makes this whole thing even worse. Sorry ChamSys, you deserve better.


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## len (Feb 24, 2012)

jpk said:


> OK with slow data rates like DMX512 this effect will only be an issue with long cable runs I'd never run a system without line termination.



True. Except that I typically don't have "long" cable runs. Event lighting is a different ballpark than, say, concerts or theater. It's very unusual for someone in my segment to make a cable run between fixtures of more than 50'. Most of the time I have 15' - 25' between the controller and the first fixture, if that. My total cable on most jobs, even with 36 - 48 fixtures, is less than 750' total. Stage work is obviously different. You may have 300 - 500' of run before you get to the first fixture.


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## headcrab (Feb 24, 2012)

bishopthomas said:


> On the flip side, however, DMX cable works just fine for microphones. I'm doing an audio gig on Sunday and will probably be using all DMX cable, only because it's more convenient at the moment. What is the difference in construction between the two varieties? The DMX cable I have just seems like twisted pair mic cable with a braided shield. I know there's something in there causing all that data goodness, but can't tell from the stripped 1/2" on the end.



We had a show in January where we had mics farther from the console than we had mic cables. We also have made several cables from cat5e (3 pin xlr connectors) which we generally use for DMX, but I used them for the mics this time. Granted, it may work until it doesn't, but we had no issues with phantom powering mics on this cable.


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## gafftaper (Feb 24, 2012)

headcrab said:


> We had a show in January where we had mics farther from the console than we had mic cables. We also have made several cables from cat5e (3 pin xlr connectors) which we generally use for DMX, but I used them for the mics this time. Granted, it may work until it doesn't, but we had no issues with phantom powering mics on this cable.



My understanding is that cat5 is a low capacitance cable and although it doesn't technically meet the DMX 512 standard it can be used for long DMX runs without the worries of Mic cables. There are several old threads around here about making DMX cables from cat5. So, it should actually be superior to mic cable.


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## mstaylor (Feb 24, 2012)

gafftaper said:


> My understanding is that cat5 is a low capacitance cable and although it doesn't technically meet the DMX 512 standard it can be used for long DMX runs without the worries of Mic cables. There are several old threads around here about making DMX cables from cat5. So, it should actually be superior to mic cable.


I will leave it to somebody that knows more than me but I thought you could only use cat 5e for conduit runs so it is shielded.


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## Van (Feb 24, 2012)

mstaylor said:


> I will leave it to somebody that knows more than me but I thought you could only use cat 5e for conduit runs so it is shielded.



Speaking as a former Field Tech for Rosco/ET, We used Cat5 for in-wall aplications. Any permanent install was done with a Belkin # 65XXXXX Crap I can't remember the number now. But yes Cat5 was completely acceptabel for DMX runs. I would not use a solid wire Cate5 cable for Temporary runs, however, as the potential for breakage exists.


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## sk8rsdad (Feb 24, 2012)

mstaylor said:


> I will leave it to somebody that knows more than me but I thought you could only use cat 5e for conduit runs so it is shielded.



EIA-485-A, upon which DMX512 is based, does not specify the need for a shield. It uses differential signalling to minimize the impact of noise or interference. There are other reasons why conduit may be desirable, but being a shield is not one of them.


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## headcrab (Feb 24, 2012)

Van said:


> Speaking as a former Field Tech for Rosco/ET, We used Cat5 for in-wall aplications. Any permanent install was done with a Belkin # 65XXXXX Crap I can't remember the number now. But yes Cat5 was completely acceptabel for DMX runs. I would not use a solid wire Cate5 cable for Temporary runs, however, as the potential for breakage exists.



Indeed. All the portable cable we have is stranded. I only use solid for permanent runs.


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## gafftaper (Feb 24, 2012)

In fact, you can purchase some handy little adapters that go from RJ45 to XLR 3 or 5 pin (male or female) for around $15. Pop a Cat5 (or better) cable in any length on the other end and you are good to go with a long distance cable run, for a lot less than traditional DMX cables, without the risk of signal loss in a mic cable.

Here's a link to those adapters for $13.25 from Production Advantage. I designed a small permanent system that's been using them for about a year now with no problems. I ran Cat5e through the walls and installed RJ45 jacks where I needed them and then used short stranded cat5e cables from the jacks to the dimmers/console. Cheap and easy compared to hundreds of feet of standard DMX cable.


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## KeeperoftheKeys (Feb 25, 2012)

len said:


> True. Except that I typically don't have "long" cable runs. Event lighting is a different ballpark than, say, concerts or theater. It's very unusual for someone in my segment to make a cable run between fixtures of more than 50'. Most of the time I have 15' - 25' between the controller and the first fixture, if that. My total cable on most jobs, even with 36 - 48 fixtures, is less than 750' total. Stage work is obviously different. You may have 300 - 500' of run before you get to the first fixture.


Maybe I'm misreading you, but the way I'm understanding you it sounds like you think a long cable run is determined by distance to first fixture.

The distance is from console until the end of the run or until the booster/signal splitter on the line (and from there it is again until the end of the run), the fixtrures are supposed to just pass the signal through without boosting, splitting or anything else.
You could almost see them as very expensive cable couplers (that happen to not really be needed), a 750' (250m) run, though not yet being at the absolute limits of the DMX standard is still quite a long run....

As far as CAT 5e goes I believe the recommended practise said that the standard recommends to stick to the same specs as "normal" cat 5e runs, ie. no more then 90m in walls and no more then 100m total cable run, this partially to make sure that a decision to upgrade to an ethernet-based network will not involve having to redo cables.
Other then that there is even a recommended pinout for rj45 connectors.


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## avery (Feb 25, 2012)

mstaylor said:


> The fact is you can do it thousands of times and it will be fine, then one night it will go south.



You also just described a normal 5 pin DMX run scenario.

I use DMX over mic cable for the simple reason of not having to worry about the audio guys taking my cable.


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