DMX Over Cat5, Pt. 2

Last time around, we talked about using Cat5 cable to distribute DMX signals. In that implementation, it is really cable replacement. Instead of pulling DMX cable (not mic cable—there is a difference), we pull Cat5 for our backbone distribution runs. Fixture to fixture cables are normal DMX cables. Today, I want to talk a little bit about using Ethernet to distribute DMX. This will be an overview article as there is way too much information to contain in a single post. Also, some of the standards are still evolving, and it’s not always simple, especially when mixing multiple manufacturers. Come to think of it, we need to do a podcast on this…

Here is a basic DMX network diagram. This is courtesy of Pathway Connectivity. 

Here is a basic DMX network diagram. This is courtesy of Pathway Connectivity

The Original Ethernet—DMX Protocols

In the beginning, we had things like: 

  • Strand Shownet
  • ETC Net1
  • ETC Net2
  • ArtNet
  • Pathport

Each of those protocols use Ethernet wiring and switchgear to distribute multiple universes of DMX throughout a facility. All of them require some time of break in and break out adapter, as well as at least one Ethernet switch to get all the nodes talking to each other. In and of themselves, they were fine. The problem was, none of them talked to each other. Some devices could speak multiple languages, but the languages themselves were not compatible. If having an all ETC Net2 system was what you needed for example, it worked well. But introducing another standard into the mix was problematic. 

Still, those protocols worked well. They offered up to 128 universes, unlimited outputs, signal management (splitting, routing, prioritizing), and because it was all based on Ethernet standards, it was inexpensive to install and manage. So far so good. But you were using Ethernet, and RJ45 connectors aren’t the most robust. And Category cable is fragile compared to a regular DMX cable. 

The New Hotness—ACN

As often happens, when engineers see protocol soup like we have above, they look for a way to create a new one that will do everything the old ones would do, and more, and do it easier. That’s the promise of ACN. ACN stands for Architecture for Control Networks and defines a series of nested Protocol Data Units—a whole series of TLAs (Three Letter Acronyms) defining how data gets moved around.

What’s cool about ACN is that it is media agnostic; you can use whatever cable you want. It’s designed to be interoperable, so multiple manufacturers equipment can be used together. It’s supposed to be plug and play, which simplifies setup. It’s also two-way, meaning the end devices can report their capabilities to the controller, and the controller will know what to do with it. In theory, this means we can get rid of fixture libraries someday. 

ACN uses an Ethernet backbone, so configuration and system architecture is familiar. I’ve been telling you that as a technical leader, you’re going to need to know more about networking. We know that’s true of audio, and it’s becoming more and more true of lighting and media servers. 

What’s Available Now?

Like many new standards, it will take time to implement. While there are some media servers and the like on the market that use ACN, there are few fixtures that do. Hopefully that changes in the next few years. Right now, we have ETC’s variant of ACN known as Net3. Pathway Connectivity uses sACN (Streaming ACN) in their Pathport products. And believe it or not, these two can talk to each other!

The good news is that we can install ACN backbone systems now, and simply break in and out to DMX as needed. Someday when ACN becomes commonplace on fixtures as well as controllers, we remove the adapters and everything talks ACN. And this is happening; many of the Jands consoles for example, already speak sACN and will simply output their DMX universes straight to the network. 

This is an exciting time to be in this industry. I was with a friend the other day and he showed me an installation that required hundreds of universes of DMX to manage. There’s no way anything like that would even be conceivable using regular old DMX. But with ACN, it’s easily possible. 

If you want to learn more about this, check out Pathway Connectivities Resource page. They have some articles and a Power Point presentation with good info (it’s where I got some of this content—thanks for that, guys!). Now is a great time to begin learning more about ACN, as it will be the standard going forward. Hopefully, we don’t have to wait 10 years before we start seeing native ACN fixtures…


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DMX Over Cat5, Pt. 1


DMX. That now ubiquitous way of controlling our lighting fixtures. While the standard of DMX is pretty well established—at least in terms of the speeds, number of channels and controls—there are still plenty of variables. Fixtures can have 3-pin XLRs on them, or 5-pin. Or both. Sometimes, the in and out jacks on a fixture are simply wired together and it doesn't matter which is which. Other times, they are active and you can't plug in to the out jack and visa versa. And while you can get away with running DMX over mic cords for shorter distances, it's not recommended for longer runs. 

Over the next two posts, we're going to talk about a few ways to run DMX from FOH to fixtures. In this post, we'll look at using Cat5 cable instead of DMX cable. Next time, we'll consider using a DMX networking system, which also used Cat5, though in a very different manner. 

Now, I should point out that when we're talking about using Cat5 for DMX cable, I am referring to the longer, backbone type runs in a system, not fixture-to-fixture jumpers. In most DMX systems, you will have a run or two (depending on universe count) from FOH to the stage, then the signal hits an Opto-splitter and is distributed throughout the stage and house lighting. At least that is what should happen; I have seen systems where there is one run from the console to the first fixture, and the DMX is daisy chained throughout every single system in the room. 

While that can work, it's not ideal. Once you get past about 18 fixtures in a DMX chain, things can get weird. Not always, but sometimes. For this reason, it's better to keep the fixture count lower and use a proper splitter to give you multiple branches of the DMX universe in your room. 

I should also point out that a terminal block or wire nuts do not a proper DMX splitter make. You really want an active signal splitter that not only sends out an exact copy of your DMX signal to each port, but also isolates the ports from each other. That way if you have a problem on one branch, the whole system doesn't go down. 

With those disclaimers and background, let's consider the first way we can use Cat5 cable in our DMX system. 

Cable Substitution

The most straight-forward use of Cat5 in a DMX system is just a simple cable replacement. Instead of pulling standard DMX cable through the conduit, pull Cat5. There are several advantages to this. First, Cat5 is a lot cheaper than DMX cable. Second, it's a lot easier to pull than most DMX cable due to it's slippery outer jacket (one that's designed to be pulled through conduit). Cat5 is also readily available in long lengths just about anywhere. 


When using Cat5 cable in a DMX system—really any cable—it's important to follow proper termination procedures. You can solder Cat5 cable to XLR plugs, but it's important to pay close attention to the cable pairs and pinning. The folks at Pathway Connectivity provided this chart, which I've used for all my jobs with great success.


Example System

So let's look at a simple system as an example. We would come from our lighting console to an opto-splitter, then out to each branch of fixtures over the stage or house. This is a simple, single universe system, so we'll pull one run of Cat5 from FOH to the stage where the opto-splitter lives, then run standard DMX cables to the fixtures. 


As you can see, it's pretty simple. Next time around, we'll use Cat5 to it's full advantage, and I'll show you how you can get 64 universes on a single Cat5.

By the way, I built this whole post on my iPad while stuck in an ice storm in Nashville.  

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