DMX Cables

When it comes to present a certain scenario, an event or premises attractively in the proper light, it is definitely helpful to delve a little deeper into the subject of DMX technology.

Basically DMX (Digital Multiplex) is nothing else than a standard protocol that controls the digital signal transmission between a transmitter featuring a DMX output and lighting equipment with DMX input (scanners, floodlights, moving heads, dimmers, etc.). When several spotlights are used, this happens by means of various serial interfaces (e.g. RS232/422/485) at a transmission rate of 250 kbit/s. The control signals "tell" the spotlights, so to speak, which function they should perform.

To transmit these control signals, corresponding appropriate cables, i.e. DMX cables, are used. The characteristic features of DMX cables comprise, among other things:

  • they comply with the AES/EBU standard (specification for the transmission of audio signals between different devices)
  • they are shielded accordingly 
  • they feature a balanced line with an impedance of 110 Ω
  • they are configured according to the official DMX512/A standard (512 control channels) and come standard with 5-pin connectors (mostly with 3-pin assignment).

A common question: can microphone cables be used for DMX transmissions? Essential factors to be considered are, among others:

  • if the characteristic impedance has an impedance value of 110 ohms, it is in principle possible to use a microphone cable for DMX transmissions. If not, disturbances caused by DMX signal reflections can occur.
  • For DMX the control signal base frequency is 125 kHz, for microphone cable it is many times lower. This also generally affects the signal transmission.
  • If the wires inside the microphone cable are not twisted, a stable DMX signal transmission becomes more difficult the longer the signal paths are (due to the higher susceptibility to interference).

All things considered this shows that, when it comes to professional applications, if you want to be absolutely sure that every control signal will definitely arrive at the spotlight as sent from the source, you should always use a proper DMX cable. Then you can really be sure that you won’t leave anyone in the dark.
And the same is true vice versa: in principle, a DMX cable can be used as a microphone cable - but it is important to note (!) that the ohmic resistance, i.e. the level attenuation must be adequately low! So, to be on the safe side, the principle "cobbler stick to your trade" should be applied here as well. Microphone cables should basically only be used for microphones and DMX cables for the control of spotlights.

By the way, Ethernet cables (category 5 / category 6 / category 7) have been used more and more frequently for DMX transmissions for a couple of years now. This trend will probably become more and more important in the future.

Another advice: keep in mind that the logic of the DMX standard in the audio area is just the opposite of the XLR logic as a DMX transmitter features a female, the receiver a male connector.