thinkoutside Posted July 5, 2006 Share Posted July 5, 2006 There a lot of discussion about DMX cables on here but I’m still somewhat confused. There seems to be some love of a hard and fast never changing DMX standard in these forums but personally I don’t care about the semantics I just care about my lights to work properly. With that in mind, does the extra 2 cables within a 5 pin DMX cable add any performance improvement over a 3 pin cable that supposedly has its 3 wires twisted the same as the DMX standard and is labeled, rightly or wrongly DMX? If so I personally see no reason for the cables to have the extra two wires if they are not serving a purpose of improving performance. It would seem to me that having a 5 to 3 pin converter at each end of every cable in the series would lead to more signal loss than just using all 3 pin cables. Here are some cables on eBay that seem to be far cheaper than even the ones that you make yourself that were pointed on in the forums. Are these not as good? Every industry has a product that stands out as the standard in its field. Is there not a high end producer for DMX cable that stands out? http://cgi.ebay.com/8x-R10-XLR-CABLE-CABLE...1QQcmdZViewItem Link to comment Share on other sites More sharing options...
PeterT Posted July 5, 2006 Share Posted July 5, 2006 As a rule a standard DMX cable only has three wires. a Signal+ or hot, a Signal- or cold and a screen, that's it.I believe the 5 pin plug was used (and feel free to correct me if I'm wrong) as a way of differentiating DMX signal cable from standard microphone cable as in big installations the two are not really interchangeable. Pulsar did start to use pins 4 and 5 in their systems a while back to carry a voltage (24 I think) but there was much Wailing and Gnashing of teeth so whether this is still the case I don't know. Most manufacturers have stuck with the 5 pin standard for DMX, it was only really Martin who had to be awkward and their newer products now have both 3 and 5 pin. All that said Usitt Standard DMX cable has three wires regardless of the plug on the end Link to comment Share on other sites More sharing options...
Brian Posted July 5, 2006 Share Posted July 5, 2006 Most 5-pin DMX cables are made using 3-core cable. You can use whatever connector you want with no difference in performance. However, the type of cable used will affect things and in my experience most of the budget pre-made 3-pin 'DMX' cables use what is in effect microphone cable. In many many setups this will not cause any problems most of the while. The problem with the DMX standard is that there is no error checking on the data as received so any errors will show themselves. Link to comment Share on other sites More sharing options...
Liam FitzG Posted July 5, 2006 Share Posted July 5, 2006 It boils down to resistance, as long as the cable is data cable and not mic cable it's ok. Having cores that are not used has nothing to do with the ability of the cable to pass the signal. Mic cable has high resistance to improve sound quality, which is bad for data transmission. DMX is designed to be terminated with a resistor across the send and return, if the cable it's self is high resistance, this will lead to intermittent reflection of the signal.So regardless of how many cores it has and how many pins are in the termination, mic cable is bad for use in lighting systems. Liam Link to comment Share on other sites More sharing options...
Brian Posted July 5, 2006 Share Posted July 5, 2006 It boils down to resistance, ... [PEDANT]actually it's capacitance that matters. :D [/PEDANT] Link to comment Share on other sites More sharing options...
Andrew C Posted July 5, 2006 Share Posted July 5, 2006 It boils down to resistance, as long as the cable is data cable and not mic cable it's ok. Having cores that are not used has nothing to do with the ability of the cable to pass the signal. Mic cable has high resistance to improve sound quality, which is bad for data transmission. DMX is designed to be terminated with a resistor across the send and return, if the cable it's self is high resistance, this will lead to intermittent reflection of the signal.So regardless of how many cores it has and how many pins are in the termination, mic cable is bad for use in lighting systems. LiamThat is wrong in just so many ways I'm not even going to start! Use 5 pin connectors, and RS485 cable. End of, unless your kit doesn't comply with the standard, in which case use 3 pin. And do terminate the run. Link to comment Share on other sites More sharing options...
Oovis Posted July 5, 2006 Share Posted July 5, 2006 If so I personally see no reason for the cables to have the extra two wires if they are not serving a purpose of improving performance. It would seem to me that having a 5 to 3 pin converter at each end of every cable in the series would lead to more signal loss than just using all 3 pin cables. There's no reason why you can't use twin + screen cables (which is what I assume you mean by 3 pin cable) if they are of the correct variety for DMX, I suspect most of us do, but the latest USITT standard says it must have a 5 pin connector on it to be called DMX. Link to comment Share on other sites More sharing options...
MarkPAman Posted July 5, 2006 Share Posted July 5, 2006 Mic cable has high resistance to improve sound quality................ What? Where can I get some? Mine must be the wrong sort! :D Link to comment Share on other sites More sharing options...
thinkoutside Posted July 5, 2006 Author Share Posted July 5, 2006 Thanks guys for getting back to me so quickly. So am I to conclude that because no one on here knows what the quality of the eBay cables I posted they may very well be wired like standard mic cables and therefore not be as reliable? I have purchased a handful of Martin lights and will likely buy more of the same in the coming months. Everything I have purchased so far has only 3 pin connections on them. We should put a list together of all the cable that the group knows is high quality. This list could include a category of finished ended cables and cable that people could use to make their own cables. I have seen some people post stuff they use claiming that they have had good luck with it but I have no way of knowing which cable is best for the money. With countless reviews of every other product in the industry are there not any cable reviews? One other question. Are XLR cables always considered to be mic cables or do they sometimes come twisted form that would be safe to use for large DMX setups? I'm trying to get all the terminology straight. BTW: Naturally I was planning on terminating my ends. I'm not looking to cut corners. To the contrary, I'm looking for high quality at a reasonable price. Link to comment Share on other sites More sharing options...
Andrew C Posted July 5, 2006 Share Posted July 5, 2006 Quality isn't the issue, it is what the cable is designed for that you need to consider. The most expensive microphone cable is unlikely to be "to specification". Have a quick read here at AC Lighting. There are other makes, suppliers etc. All that said, I do use, successfully, a link made of Canford HST when the desk is in the auditorium. "T" ed into the system too...One other question. Are XLR cables always considered to be mic cables or do they sometimes come twisted form that would be safe to use for large DMX setups? I'm trying to get all the terminology straight.XLR describes a connector type, not a cable. There are 3-7 pin variants used for different purposes. Have a look at the BR Wiki for more info. Link to comment Share on other sites More sharing options...
Andrew C Posted July 5, 2006 Share Posted July 5, 2006 My apologies. But really! Mic cable has high resistance to improve sound quality, ... if the cable it's self is high resistance, this will lead to intermittent reflection of the signal. All cables (except the ballast used for florescent inspection lamps) is designed to have the lowest possible resistance given the size/weight/cost trade off. The reason DMX and other types of high frequency data systems are terminated is to prevent reflection from the end, nothing to do with the resistance of the cable. Link to comment Share on other sites More sharing options...
Tom R Posted July 5, 2006 Share Posted July 5, 2006 I think I'm right in saying one of the major reasons for 5 pin DMX being the international standard is that DMX-A (or whatever the revised DMX standard is called) allows for feedback via the other 2 pins? I am sure that someone will correct me here but I was sure that was the reason... Whether 5 pin is right or wrong it is the standard and I just wish people to stick to the bloody thing so you dont have to work your rig around the amount of adapters you own and seperate rings for Martin fixtures to Robe because its easier with their different pins...argh rant over! Link to comment Share on other sites More sharing options...
benweblight Posted July 5, 2006 Share Posted July 5, 2006 Yes, in future (and on some devices already?), there may be RDM (remote device management), which will allow feedback from devices Lots of manufactures use 3 pin, lots use 5 pin (many desks have them, for instance), theres no way round that so arguing about this is a bit pointless(manufacturers are rarely keen on setting standards). 5 pins are also used as cable for stereo mics, with two pairs. Link to comment Share on other sites More sharing options...
Brian Posted July 5, 2006 Share Posted July 5, 2006 I think I'm right in saying one of the major reasons for 5 pin DMX being the international standard is that DMX-A (or whatever the revised DMX standard is called) allows for feedback via the other 2 pins? I am sure that someone will correct me here but I was sure that was the reason... Yes, in future (and on some devices already?), there may be RDM (remote device management), which will allow feedback from devices RDM does not use the second data pair. It is carried over the main DMX link. It's done this way because hardly any DMX installations are done with 2-pair cable. Link to comment Share on other sites More sharing options...
thinkoutside Posted July 5, 2006 Author Share Posted July 5, 2006 I see no point in keeping to a standard when technology allows us to make improvements and form new standards. Ironically form what I understand the other two pins never had a purpose in the first place so I’m confused by why a 3-pin standard was not used from the outset. I see no point in running 2 extra lines of cable inside just to satisfy a standard if they are not going to be used. Why not standardize the most logical and technologically advanced format as possible. Given 3 pined cable that is twisted correctly has everything the light needs and nothing extra would that not be the best format to use going forward? I have to conclude that this is Martins reasoning for pushing the 3-pin design. Am I missing something here? Link to comment Share on other sites More sharing options...
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