Control/Dimming DMX Advice

JLang76

Member
I'm a high school student, so please pardon my limited understanding of DMX complexities.

I'm working on lighting a small stage (10'x10') for relay for life event. My equipment is a MyDMX 2.0 USB converter, 10x Chauvet SlimPAR, 2x Elation DesignSpot 250, a 3pin terminator and a ton of XLR cables.

Will it work to have a daisy chain of all these fixtures running through mic cables? If itll work best then I have the option to set up FOH right next to the stage, but ideally I would like to run it through an existing audio snake box up to the press box of the stadium. I figured that's probably pushing it though, am I correct?

I know it's less than ideal, but it's what I have available and I have no budget or anything.

Thanks!
 
Yes, the snake should work fine but if you are going to go through with it, I would at least test it before the event. You're only going to have issues once you send audio through the snake at the same time. I haven't had any experience with this exactly, but I know there can be cross-talk between cables that will transfer weird noises (DMX signal) to the cables with audio from the cables with DMX and out the PA. If you have enough DMX cable (or audio/ 3 pin cable), you can just run another data line for lighting out to the stage. Or if not, set up a lighting desk near the stage for the safest option. Personally, if I was getting paid, I wouldn't run it through the snake.
 
Yes, the snake should work fine
This information is not accurate. You’ll run into problems if you run DMX over an audio cable or an audio snake. Use dmx cable for dmx ALWAYS. CAT5e or higher is also suitable (Which May also be available in the stadium). But you will find yourself with issues if you run everything through audio cables.

Also, make sure to terminate your chain at the end, especially since you plan on doing a longer run.

Once again, DO NOT use mic cables for DMX.
 
Yeah I had a feeling the snake would do some wacky things. I think I'll just skip it and set up my laptop down on the field.

I really don't understand how to run DMX over CAT5. If you don't mind, could you explain it in basic terms? Do you need to make custom cables with the right ends on them?
 
Yeah I had a feeling the snake would do some wacky things. I think I'll just skip it and set up my laptop down on the field.

I really don't understand how to run DMX over CAT5. If you don't mind, could you explain it in basic terms? Do you need to make custom cables with the right ends on them?
Yes - or acquire adapters and use ethernet CAT5 (or later) patch cords. http://www.sescom.com/product.asp?item=DMX-3XM-CAT5

I wondered if you audio snake was CAT5, but I guess not, or at least Brent doesn't think so.
 
I wondered if you audio snake was CAT5, but I guess not, or at least Brent doesn't think so.
Ahh yes, I jumped to a conclusion. So I’ll ask, is your audio snake cat5e or higher?

If you know how to solder and can do well at it, you can put dmx ends onto cat5e. I don’t recommend this in portable applications because cat5 is pretty rigid but it will work well as an installed solution. ETC has the pinout diagram on their website. I’ll try to add a link later (I’m on my mobile now).

Two things that often don’t get taken into consideration when it comes to using mic cables for dmx is that a) dmx Cable and mic cable are a different gauge. And b) Dmx is a digital signal where as analog audio is, well, analog.
 
Although you really, REALLY should be using DMX cable, if all you have available is mic cable, you might get by, it will probably work (until it doesn't).
If you haven't yet done so, go the the wizard of DMX and learn the whys and wherefores.
www.dfd.com/info.html
Start with the Dr. DMX Papers and go from there.
Running lights from the stage isn't ideal but it can be done. One thing to consider, don't just look at the light and what it hits, also look at the shadows. You can even call followspots from side stage. Good luck and keep learning.
 
I don't think the snake is, but I'm not totally sure and of course there's no documentation anywhere. I'll just plan on skipping that and moving onto the field. Most of the performances are small, the idea is really just entertainment while people walk the track. Most audience won't actually be standing or sitting in front of the stage at all, so I'm not going to be getting too insanely complex anyway.

I appreciate the advice and reasoning behind the DMX theory. Like I said earlier, I really have no option but to use audio cabling. I know it's been done with this particular rig before with no issues, but that of course doesn't mean I won't have any issues. Not thrilled, but all the equipment is borrowed so it's not even worth it to suggest we purchase cables for one day and take money that would go to ACS.
 
The one option not mentioned - and I know money is tight - is wireless. I believe its possible to rent (or beg, borrow, or steal) a transmitter and receiver pair. Just an option. You could at least ask your local rental dealer.
 
In an ideal world, only DMX cabling should be used for carrying DMX signals. However, although far from ideal, I have run DMX through an audio snake (before I knew better). However, it was only a 75' snake that only had a few channels of audio running in it. I would presume the pressbox of the stadium is going to be much further and would likely be problematic. (I'm in Texas, so even our HS stadiums can be quite large) Moving onto the field is definitely your best option for a budget solution here (though, using DMX cabling - even if it has XLR connectors - is still the best approach).

As others have said...it can work...until it doesn't. For our rig, we mostly had good results with occasional issues when dimming some dimmer packs. I've also seem some cheap import LED lights be more picky about their DMX signals. As has already been suggested, testing ahead of time is probably a good idea (even if it's been used in this venue previously) just to ensure things haven't changed too much.

I think Bill's suggestion of trying to find a place that might be willing to loan you a small wireless DMX rig (single transmitter, single receiver) is a great solution - especially for a non-profity/fundraising event.
 
Two trip-up points. Some audio cables have pin 1 and the shell connected. This could be a real problem when used for DMX. Likewise, some snakes tie all the pin 1 connections together, this may raise some issues with ground paths when DMX is run through it. So, even if the DMX signal handles the abuse of going through cable that is the wrong impedance, you may be headed for trouble when the snake comes into play. I would just run a separate line to the stage outside of the snake.
 
Thanks for all the advice guys.

From Pennsylvania, not LV. I'm going to skip the snake and run from FOH. Thinking about it, they're planning on putting a tent over the stage, so I would have absolutely no visibility from the press box anyway. I'll figure out an exact solution.

Thanks again for the help and patience
 
DMX cable is 120 ohm, low capacitance. This is necessary for the sharp transitions of the square wave pulses which make up the DMX bits to propagate cleanly and successfully. DMX is a 250kb protocol.

Microphone cable is lower impedance, and has higher capacitance per foot. Microphone cables carry signals up to about 20khz, so they can be spongier in their propagation response. In other words, if the corner of a square wave starts to get rounded off more like a sine wave at The DMX pulses are at a much higher frequency (10x that of analog audio).

There’s a 3rd solution to consider as well. Much theater DMX travels over Ethernet. You might be able to borrow a pair of DMX to EN gateways and then run Cat5e or piggyback on existing EN for future incarnations of this.

I echo the concern about using WiFi ...if you go wireless, use the 900 MHz or a frequency hopping system that can steer around the interference.


Finally, never use dmx to control anything like pyro, flash pots, or moving scenery ... it’s not safe. There are more robust 2way failsafe command systems for these uses.

Have fun!
 
And never use DMX to control airplanes, self-driving cars or portable gas ovens; Coffee makers are okay.

Okay, but seriously. Just use the mic cable, don't use the snake, probably use the terminator. Terminators can often fix the sin of using bad cables. Though sometimes the signal will be just strong enough to work fine WITHOUT the terminator, and termination will actually cause problems. So try it both ways and make sure everything is solid ahead of time. With the small number of fixtures and keeping cable runs short, I would be willing to put $20 on you having no problems, even though its mic cable.


...
There are LOTS of pyro products and motion control products that are controlled by DMX(completely safe when done correctly, though people on this forum will argue vehemently against this because they don't know how to use the Google, and have limited real-world experience). Pyro and motion control is far beyond the scope of knowledge of this forum and requires extensive knowledge and GOVERNMENT LICENSING, in the case of pyro. It should go without saying that it is not something amateurs should be trying, without the proper training and oversite from professionals. Though the OP never mentioned anything about either of these things, so I really don't know why it was mentioned in the first place, but blanket statements about "never do this with DMX; its unsafe" are categorically incorrect and do not serve to educate anyone on the subject.
 
And never use DMX to control airplanes, self-driving cars or portable gas ovens; Coffee makers are okay.

Okay, but seriously. Just use the mic cable, don't use the snake, probably use the terminator. Terminators can often fix the sin of using bad cables. Though sometimes the signal will be just strong enough to work fine WITHOUT the terminator, and termination will actually cause problems. So try it both ways and make sure everything is solid ahead of time. With the small number of fixtures and keeping cable runs short, I would be willing to put $20 on you having no problems, even though its mic cable.


...
There are LOTS of pyro products and motion control products that are controlled by DMX(completely safe when done correctly, though people on this forum will argue vehemently against this because they don't know how to use the Google, and have limited real-world experience). Pyro and motion control is far beyond the scope of knowledge of this forum and requires extensive knowledge and GOVERNMENT LICENSING, in the case of pyro. It should go without saying that it is not something amateurs should be trying, without the proper training and oversite from professionals. Though the OP never mentioned anything about either of these things, so I really don't know why it was mentioned in the first place, but blanket statements about "never do this with DMX; its unsafe" are categorically incorrect and do not serve to educate anyone on the subject.
@DavidJones Surely you remember @Janelle Fleenor 's Dad's DMX controlled coffee percolator from a few years back? @Janelle Fleenor Where's that auto link??
Toodleoo!
Ron Hebbard.
 

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