DMX Cables

[zijital]

Anyone know about DMX cables? (The 5pin XLR cables used for controlling lights.)

I use a Datavideo switcher (HS-2000) that uses those cables for the headsets / tally.

We ordered a few Hosa 5 pin XLR cables from B&H, but they only have 3 wires in them. (See attached photo.)

Obviously they don't work with the switcher as the switcher needs 5 wires for the headsets / tally. At a shoot with long cable runs I borrowed a DMX cable on a multi cam shoot from an AV / lighting tech & everything worked perfectly.

This seems like they're bad cables. Unless, does DMX use a 5 pin connector, but only 3 wires? It doesn't seem to make sense that you'd have empty pins with no wires connected to them.

 

[dwiener]

DMX only uses 3 wires. Some companies use 3 pin xlr's for DMX, most use 5 pin, and I've also seen RJ​45 connectors used as well.

 

[bclighting]

It doesn't seem to make sense that you'd have empty pins with no wires connected to them.

Well that is a long story but the short of it is that when DMX was coming into being they picked 5 pin to keep it separated from mic cables. Over the years there have been attempts to use the second pair for talkback data. Most of that has gone by the wayside now. Even though the second pair is not used I always build my DMX cables with all 5 pins connected. I use true RS485 2 pair data cable. My opinion is that is the right way to do it and 3 pin XLRs are only for the noise boys.

 

[zijital]

Thanks for the replies. I do find it kind of silly that the main reason to use 5pin is to try to idiot proof DMX with 5pin XLR lighting from 3pin XLR audio. Is there really such a risk that a mic level or line level could damage lighting equipment? Or lighting equipment damage audio equipment?

It is good to know that I just have to hunt out quality DMX cables that have 5 wires in them to use with the DataVideo switcher. Disappointed that B&H Photo / Hosa didn't label their cables in the product description that the ones we purchased only had 3 wires.

 

[bclighting]

Its not just the connector but also the type of cable. Real DMX cable is designed for digital data and is shielded as well. Although the truth of the matter is DMX can run down just about anything. DMX on barbed wire is a running joke in the lighting community and it is not that far from impossible.

DMX is a 5v system, mic with phantom is 48v so there is the possibility that damage could occur. Using 3 pin XLR started in the DJ market so they didn't have to buy more cables. Now it is somewhat synonymous with lower end DJ and Chinese lighting equipment.

 

[dwiener]

Echos on the line could be a problem, thats why the end of a run should be terminated. And the wrong cable type might work or might not. Audio cable might not have the bandwidth needed for a digital signal.

 

[zijital]

Audio cable might not have the bandwidth needed for a digital signal.

yeah, but I still feel like it is trying to idiot proof professionals. HD-SDI uses BNC cables. If you need a long HD-SDI run, you need high quality cables. If you try to do it with cheap cables you'll hit a digital cliff & it is the user's fault for using the wrong cable. If you're doing a 10' run, you can probably use the cheapest of the cheap BNC cables & be fine.

I'm personally glad that when they were designing HD-SDI, they didn't try to come up with a new type of connector just to prevent people from using cheap BNC cables that don't work with HD-SDI.

If DMX used a 3pin connector & normal quality XLR audio cable's can't carry the digital signal of DMX, then the user should be responsible for buying & labeling their own cables to signify which cables are for DMX & which are for audio.


It just still seems crazy to me that they'd design DMX with 5pin connectors solely for the purpose to protect user's from them selves. But again, this is just my personal opinion.