Should I trust my installed wire?

[fumb3l]

I'm looking to run some dmx cable up to my cat walks in my theatre but I don't know if I should trust my instaled lines. They are audio lines but I know you can use regular Mic cables in a pinch.

Also I here not using dmx rated lines can damage something but what does it damage. The lights? The cable? What?


Thanks: fumb3l

 

[microstar]

For a permanent or semi-permanent install I would never use audio lines for DMX. You are risking having your DMX fixtures respond erratically at entirely inappropriate times, like during a performance. Using the audio lines will not damage your equipment, the fixtures just may not work when you need them to.

 

[STEVETERRY]

I'm looking to run some dmx cable up to my cat walks in my theatre but I don't know if I should trust my instaled lines. They are audio lines but I know you can use regular Mic cables in a pinch.

Also I here not using dmx rated lines can damage something but what does it damage. The lights? The cable? What?


Thanks: fumb3l

Short answer: no.

Long answer: no.

You need to put in proper low-capacitance DMX cable. Otherwise you run the risk of no control or flash and flicker.

DMX cable rule [HASHTAG]#1[/HASHTAG]: the crappy mic cable always works well in rehearsal. If it's going to fail, it always does so during the show.

ST

 

[MarshallPope]

In short, it will work until it doesn't. As microstar said, it won't hurt anything; it just may decide one day that it doesn't want to work. While I have run DMX over a mic snake for less-than-critical applications, I wouldn't recommend it if you have any other option. It's worth the negligible expense of at least a run or two of Cat cable.

 

[AlexDonkle]

DMX cable rule [HASHTAG]#1[/HASHTAG]: the crappy mic cable always works well in rehearsal. If it's going to fail, it always does so during the show.

ST

I think that's the theatre version of Murphy's law...

 

[NewChris]

Short answer: no.

Long answer: no.

You need to put in proper low-capacitance DMX cable. Otherwise you run the risk of no control or flash and flicker.

DMX cable rule [HASHTAG]#1[/HASHTAG]: the crappy mic cable always works well in rehearsal. If it's going to fail, it always does so during the show.

ST

What do you mean by the lights flash and flicker? Why would this happen?

 

[fumb3l]

What do you mean by the lights flash and flicker? Why would this happen?

That's a good question I'd like to know as well

 

[JD]

What do you mean by the lights flash and flicker? Why would this happen?

DMX is a one way conversation between the board and the lights. The board shouts commands and the lights (or whatever else you have attached) listen for the orders that have to do with them. Good cable is like having a conversation in your living room. Bad cable is like someone shouting at you from the other side of a noisy gymnasium. The lights, dimmers, whatever, can not "hear" the commands and often respond to what they think they heard. The results are random interpretations. A dimmer channel may have though it just heard a "full on" command and a second (or less) later, think it was suppose to be off. The results are flashes, flickers, and in the case of movers, random motions or flat-out wrong cues.
Ok, obviously I have taken some artistic liberties here, but it's probably the best way to understand what is going wrong.

 

[MNicolai]

The important thing to remember is, using average mic cable may work from anywhere between days, weeks, or years before you encounter an issue. This is why a lot of people out there will tell you can get away with it, and sometimes you can. But there's no way to know when, how, or why things will go haywire. Inevitably though, it happens at the worst moment in the most obvious and embarrassing way.

Also, whenever you contact tech support for your console, fixtures, or dimmers, expect one of the first questions to be about how your DMX cabling is set up. If you tell them you're using non-DMX grade cable, they probably won't help you troubleshoot your problems further than to tell you to replace your cabling. <Then>, they'll say if you do that and still have problems, give them another call.

In general, tech support will understandably not give you more than the time of day if there's a fundamental, egregious flaw in your system design that's capable of causing such unpredictable, seemingly random and catastrophic system failures.

So can you get away with non-DMX cable? It's possible.

Will you have dug your own grave if and when the whole system develops a mind of its own mid-show because of data corruption in the cable or interference? Absolutely, and your client or employer will remember when everything went haywire on your watch.

 

[StradivariusBone]

What do you mean by the lights flash and flicker? Why would this happen?

Doug Fleenor has two videos that explain it pretty well, but a bit more technical. A lot of it has to do with shielding from interference and the capacitance differences between DMX rated cable and microphone cable.

To view this content we will need your consent to set third party cookies.
For more detailed information, see our cookies page.

Accept third party cookies

 

[len]

There's a general rule when you want to "cheap out" on something, and based on an old adage:

Act in haste, repent in leisure. Or as JFK was purported to have said: If you don't have the time (or money in this case) to do it right, how will you have the time to do it over?

 

[RileyChilds]

I'm looking to run some dmx cable up to my cat walks in my theatre but I don't know if I should trust my instaled lines. They are audio lines but I know you can use regular Mic cables in a pinch.

Also I here not using dmx rated lines can damage something but what does it damage. The lights? The cable? What?


Thanks: fumb3l

I would recommend that you pull though CAT5e or 6, I have used it for permanent installs and temporary installs. It can even be soldered or crimped straight onto standard 5pin XLR connectors and wall plates! Of course all this depends on how lazy the contractor or electrician (arrrrgh!) who installed the system was: did they put the requisite pipes though walls, or did they do the simple stab and plaster? Never ever us mic cable in place of DMX cable for long runs. You can get a box of 1000ft of CAT 5e from your local home depot for about $50-$75.

 

[JD]

Shielding is required unless you are running solo in metal conduit. (See Dr DMX video above.) Outside of that, Cat5 is great for installs where there will not be a flexing issue.

 

[wolfman005]

STP is ok to use without conduit right?

 

[StradivariusBone]

STP is ok to use without conduit right?

https://www.etcconnect.com/Support/Articles/DMX-Over-Cat5.aspx

In a perfect world you'd want it in conduit, Cat 5 is not as durable toward physical abuse as EIA-485 which is why I think they prefer it in the pipe. The thing I don't understand is that we used to use Cat 5 (and 5e) UTP all day long for network drops when I worked as a cable monkey. Does the DMX protocol not provide provide for the same common-mode rejection as in ethernet cabling? Or is just that the threshold for acceptable interference is much lower in DMX applications than in networking environments?

 

[JD]

https://www.etcconnect.com/Support/Articles/DMX-Over-Cat5.aspx

In a perfect world you'd want it in conduit, Cat 5 is not as durable toward physical abuse as EIA-485 which is why I think they prefer it in the pipe. The thing I don't understand is that we used to use Cat 5 (and 5e) UTP all day long for network drops when I worked as a cable monkey. Does the DMX protocol not provide provide for the same common-mode rejection as in ethernet cabling? Or is just that the threshold for acceptable interference is much lower in DMX applications than in networking environments?

Actually, it is the lack of error correction. You can have a high error rate on a network, but because the error is detected, the "sender" knows to resend the packet. Another problem is that DMX was born 30 years ago, and for the most part, 485 receivers and transmitters are still of that technology and stuck with it. The architecture is "backbone", which is more prone to problems, whereas current Ethernet (based on cat 5) is point-to-point so there is a dedicated transmitter/receiver combo for each data link. Also, the data is floated between two isolation transformers so noise rejection is fantastic. The overall architecture would be considered "star" as you hub out, but even the hubs have an individual interface for each line that enters it. So, basically we live with DMX as a great legacy system. For the most part, it works good so users are happy. However, comparing DMX to 10baseT (or 100baseT, etc) Ethernet is like comparing a Model T Ford to a modern race car. The road (Cat5 cable) may be the same, but it is a whole different animal.

 

[wolfman005]

Does Art-Net have error checking? Or should those ether runs also be shielded with conduit or STP?

 

[JD]

Does Art-Net have error checking? Or should those ether runs also be shielded with conduit or STP?

Art-Net works by converting the DMX signal to a network IP protocol to be run over a local network. Basically, the DMX from your board goes to a protocol converter, runs across network cabling, hits another converter which converts it back to DMX which then goes to your rack, movers, or whatever else you might have connected. The converter can be something that stands alone, or may be built into the board, rack, etc. The section of cable between the converters has error correction. The sections that are straight DMX don't. So, assuming your network cable is Cat5, it does not need to be shielded. Once the signal is converted back to DMX, it does.

 

[gafftaper]

Art-Net works by converting the DMX signal to a network IP protocol to be run over a local network. Basically, the DMX from your board goes to a protocol converter, runs across network cabling, hits another converter which converts it back to DMX which then goes to your rack, movers, or whatever else you might have connected...

Just a note for further reference, the same is true of ACN and Shownet. Some day all DMX devices will come with an RJ45 plug and the ability to directly understand ACN (the replacement for DMX). Then we will be able to simply use cheap off the shelf network cables and switches for the entire network. That will be a great day... But it seems to be a long way off.

 

[JChenault]

Art-Net works by converting the DMX signal to a network IP protocol to be run over a local network. Basically, the DMX from your board goes to a protocol converter, runs across network cabling, hits another converter which converts it back to DMX which then goes to your rack, movers, or whatever else you might have connected. The converter can be something that stands alone, or may be built into the board, rack, etc. The section of cable between the converters has error correction. The sections that are straight DMX don't. So, assuming your network cable is Cat5, it does not need to be shielded. Once the signal is converted back to DMX, it does.

I believe that the Artnet protocall is based on UDP which does not have error correction. ( it does have error detection however ). If an error is seen, the packet is simply dropped, not re-transmitted. In the case of an error the output converter ( Artnet to DMX) simply continues to send out the last valid packets it received.