Have you ever been confronted into having one of your light behaving strangely? The DJ light switch off, flicker, change color, pattern, etc. Rings a bell to you? That may be a sign that you need a DMX terminator!
A DMX terminator is an important part of any DMX DJ light system. In fact you need to terminate every of your DMX chains. This is specified in the DMX512 norm and will be needed for 90% of applications. So yes, DMX terminators are necessary.
On this page I will explain why they are important, how they work and in which particular case you may consider not installing one (though that is not recommended).
Why use a DMX terminator?
A DMX terminator prevents one of your light or fixture to have a strange behavior. If a light seems out of sync, is flickering, is changing pattern randomly, etc. it is probably because you need a DMX terminator. In fact, Adam Bennette, a famous designer of DMX products, said “Incorrect or missing termination is probably the single most common reason for faulty DMX512 systems” [1].
If you use your DJ light in “sound activated” mode, which uses the microphone to detect the music to sync, then you don’t need a DMX terminator. Indeed a DMX terminator is necessary when you put your lights in “DMX mode” and are chained thanks to DMX cables.
When in DMX mode, the light is controlled by an electric signal, numerical information, that tells the light what to do. This DMX signal is built by what is called a “DMX controller”. In a perfect world, the signal has a square shape and looks like this:
When no DMX terminator is used, the signal, when arriving at the end of the DMX chain, will bounce back or “reflect” into the cable. This is called “reflections”. Not the entire signal is reflected, only a small part of it, but that’s enough to deteriorate the signal. The information carried in the signal is therefore not clear as it should be and your lights start to behave strangely. Just picture this : your appliance receives the reflected signal as well as the original signal, it sees two numbers at once. Therefore it gets confused. It is a simplification, but helps to understand what is happening. A DMX terminator will simply stop this reflection from happening, keeping the single signal clean.
How does a DMX terminator work?
To prevent the reflection, a DMX terminator simply transform the energy of the signal into heat thanks to a resistor. In order to absorb the maximum amount of energy, the resistor has the same impedance of what DMX cable should have, in other words 120 ohms.
When to use a dmx terminator?
You need a DMX terminator if the sum of your DMX cables is longer than 590 feet throughout your chain. Below that, having one is recommended but not mandatory. Therefore, if you are a mobile DJ with not many lights and thus do not plug many DMX cables, then not having a terminator may be fine. If you do have a problem on short cables, that may be caused by a combination of issues : reflections + low quality cables + bad light fixture. In that case a DMX terminator will probably solve the issue by removing the noises in the signal, wherever they come from.The higher the cable length or number of appliances, the higher are the chances of having trouble. So do not hesitate to put a DMX terminator when you increase the complexity of your installation.
Please note that when having a problem, it may happen that only one appliance behave strangely. That may happen even when you placed the exact same model at several places in your chain. That tends to confuse people into thinking that the DJ light is faulty when really it was only a DMX terminator missing. The reason behind is that noises may be added throughout the chain by the other lights and slowly accumulates, light after light. Eventually the first lights were not affected but at one point of the chain, it starts to affect one specific appliance. It may also be just because one of your light is a bit more sensitive or a combination of the two phenomena. But then again, using a DMX terminator will solve the problem. So just buy one, its cheap anyway!
How much does a DMX terminator cost?
A single dmx terminator costs on average 7$ on amazon, but they are often sold by pairs. The price of a 5 pin terminator is similar to the 3 pin ones. Please note that having one terminator is probably enough for you as you only need to put it at the end of a given DMX chain. This is at least enough for mobile DJs who owns below a dozen fixtures. I would advise to buy the ones sold by pairs, it is always convenient to have two in case you lost or broke one. You can buy them here. If you want a cheaper option, there is still the possibility to build it yourself.
How to build a dmx terminator?
For the DIYers out there, it is possible to build your own DMX terminator. In fact, a dmx terminator is rather basic, it is a simple 120 ohm resistance linking the pins 2 and 3. Thus the only thing to do is buy an XLR plug and weld the resistor between the two pins. It works for both 3 and 5 pin plugs. Just make sure you buy a male plug and not a female one!
Using a DMX terminator did not solve my issue, what else do i need to check?
One common mistake is to use microphone cables, namely XLR cables, instead of DMX cables. Indeed XLR cables have the same plugs or connectors, but they have a different cable impedance. Therefore, though you can plug it and seems to work, these cables are different and should not be used.
XLR cables have a higher impedance than DMX ones, this characteristics will dampen the square signal which will affect the readings of your fixtures. Exaggerated, the phenomenon will look like this :
Thus, if the DJ light reads one peak a bit too early, then it will read a smaller value than what the signal was supposed to be. This control signal will then be interpreted into a false command, leading to a strange behavior. Using a XLR cable is a common mistake, so be careful!
If you still have problems, that may be because your cables are too long. A good practice is to keep the cumulative length below 1000 feet. A good solution for that would be to use a DMX splitter in order to have several DMX chains instead of a single one.
What about my experience with DMX terminators?
When I started as a mobile DJ for friends, I was only connecting two small derby so that the pattern of the two are in sync. My other lights were in sound activated mode. Therefore my cable length was only 20 feet long and I did not use a DMX terminator. I stayed with that installation during two years without having any problem. Some time later, with a few more lights, I did not have any problem at the beginning but eventually they showed up. At one event, I had to run a cable with a longer length than I usually do, because of the configuration of the room. This was my first time encountering DMX issues. Simply because the room configuration was different! So yeah, having a DMX terminator is always handy, because you never know what can happen. That is what I learned the hard way that day.
Do you recommend any DMX terminator?
Any terminator will do as long as it has the right number of pins and a 120 ohms resistor. This 3 pins terminator or this 5 pins version, available on Amazon, are perfect for the job!
If you liked this article, please go have a look at my article about the accessories every DJ needs! There are good examples of things to have on top of a DMX terminator.
Source:
[1] Recommended Practice for DMX512 by Adam Bennette, edited by PLASA
