dth122 Posted February 25, 2009 Share Posted February 25, 2009 I am working on an installation in a theater that has one dimmer rack and one console. They want to be able to use the console from the stage for focus and from FOH for shows. What is the recommended method for wiring a permanent DMX jack on stage and another one at FOH if the dimmer rack only has one DMX input? The simple option is to use a DMX switch at the dimmer rack, but it would be preferable not to have to switch based on the desired control location. Can I daisy-chain from one DMX jack to the other? If I run from the on-stage jack to FOH, it's probably a 175' run. I know that this will theoretically work, but in practice do I need to worry about noise or anything else coming from the unterminated line or unused jack? Would I need (or want) to terminate the unused jack (which could be either on stage or FOH)? Similarly but even easier, I could use a Y cable at the dimmer rack and a separate run to each jack point. I realize this doesn't meet the DMX spec, but I don't see the problem (aside from the aforementioned potential for noise) since only one run would be used at a time. I'm sure that this is common in installations and there is a standard method for dealing with this situation that I'm not thinking of. Thanks. - Dave Link to comment Share on other sites More sharing options...
STU007280 Posted February 25, 2009 Share Posted February 25, 2009 One option I can think of is Wireless DMX.Transmitter by the desk and Reciever at the racks.Then they can use the desk practically wherever within distance.J Link to comment Share on other sites More sharing options...
niclights Posted February 25, 2009 Share Posted February 25, 2009 Wireless is not something I would even begin to consider. It is not reliable. Personally I manually switch cables at dimmer end, but I see nothing wrong with a Y-split system in this situation. Either that or use a merger, but seems like unnecessary expense. Link to comment Share on other sites More sharing options...
Dmills Posted February 25, 2009 Share Posted February 25, 2009 A Y split will quite possibly not work reliably, due to the unterminated stub created by the unused leg of the Y. I would probably link the FOH input to a short tail by the stage input and just plug them together when working from FOH. An alternative would be to fit a DPDT switch by whichever input is close to the dimmers and wire it to switch between the remote socket and the local socket. That way you do not have a long stub to cause reflections and general problems. Regards, Dan. Link to comment Share on other sites More sharing options...
DonkiDonki Posted February 25, 2009 Share Posted February 25, 2009 Having a Y-split for DMX into the dimmers has a potential problem. If for some reason a DMX desk, or any transmitting device, ends up on both ways it could end up with some expensive damage. I'm sure at the time of installation this would be unlikely but there's no accounting for what will happen later on. You could have seperate sockets on stage and front of house and have them go through a DMX-merge unit before the dimmer (showtec do a fairly cheap one). If you end up with a controller on both lines they can be mixed as htp by the merger. This would even allow a deliberate mix of backstage & foh control to the same dimmers if ever desired. Link to comment Share on other sites More sharing options...
GridGirl Posted February 25, 2009 Share Posted February 25, 2009 We do something very similar - console in the auditorium for focus and plotting sessions, then back in the control room for shows. The way it works for us is that there's a DMX socket in the auditorium which runs through to a tail in the control room; there's a DMX line in the control room which runs to the dimmers. When the desk is in the control room it plugs straight into the line leading to the dimmers (and the tail of the line from the audi is not plugged into anything); when it's in the auditorium, the tail of the line coming from the audi is plugged into the line leading to the dimmers. Depending on where the dimmers are you may want to do it the other way, to save cable runs - a line from FOH to the stage, with a short tail on it, and then a line running from the stage to the dimmers; when you're running from the stage, plug straight into the line, and when you're running from FOH, plug the short tail on stage into the line going to the dimmers. No switcher or Y-split necessary - just make sure you label everything clearly - ours all have big labels on them which say things like "From auditorium" and "to dimmers" so that it's idiot-proof! Link to comment Share on other sites More sharing options...
KevinE Posted February 25, 2009 Share Posted February 25, 2009 I'd rather see any auxilliary socket connected in daisy-chain with the main desk connection, it's using Y connections or splits that causes signal reflections on the unused portions of the cable (due to its impedance). DMX RS485 is a daisy-chain only format. A double-pole changeover on the dimmer is also a suitable idea as the unused portion of cable will be out of circuit. I know the Y-method usually works but I thought it worth mentioning this for reference. Link to comment Share on other sites More sharing options...
J Pearce Posted February 25, 2009 Share Posted February 25, 2009 Why not have your main DMX input in the booth, then a permanent extension to the FOH plotting position. When plotting plug the flying lead of the extension into the input in the booth, then plug in FOH; when running plug straight into the booth input. Cheap, simple and doesn't involve dirty bodges which might leap up and bite you in the bottom later (when used with a different desk or more data etc). [edit]Sorry, I read plotting not focusing. In this case you'd be better to flip it round and extend from focusing to booth.[edit2]Gridgirls already said this. I shall retire to the corner. Link to comment Share on other sites More sharing options...
peter Posted February 25, 2009 Share Posted February 25, 2009 It's not a cheap solution, but what about a DMX over ethernet solution? Ethernet allows the sort of topology you require for this installation, and you can break out into DMX at the dimmers with a simple ethernet switch in the system. If you're specifying a medium-high range console for the venue, it'll probably support a DMX-over-Ethernet standard out of the box (Artnet for example, seems to be pretty much an industry standard) and then you'd just need a Ethernet-DMX box (such as our 1 Universe Ethernet Box, £245 list price) to convert out of the ethernet standard into 'normal' DMX. You could then wire the building with as many ethernet points as you want and these become DMX inputs/outputs depending on the configuration of the ethernet device plugged into the port, rather than the wiring of the system. I hope this helps - it might not be the cheapest solution, but it'll future proof the venue for many years to come. Peter Link to comment Share on other sites More sharing options...
paulears Posted February 25, 2009 Share Posted February 25, 2009 That's a very expensive way of replacing a plug and socket! My venue still has the original multiplex system cabling - D54, on 3 pin XLRs that was installed when they upgraded the cable per channel analogue 60 way board to an M24. There is a link stage left with a simple short 4" flying lead. It's been reliable for nearly 30 years and is very happy doing the same job with DMX. Peter's suggestion is a technically valid one, but a bit sledgehammer and nuttish! Link to comment Share on other sites More sharing options...
gareth Posted February 25, 2009 Share Posted February 25, 2009 Peter's suggestion is a technically valid one, but a bit sledgehammer and nuttish!Not so much a suggestion as a sales plug, though, Paul ... ;) Link to comment Share on other sites More sharing options...
dbuckley Posted February 25, 2009 Share Posted February 25, 2009 A theatre of my acquaintance have a run of mic cable from a plug at the operating position, and the cable "stops off" at the back of the front stalls where there is another plug. The wire continues on its way to a socket adjacent to the dimmers. The dimmers are plugged in (non-terminated). It all works. Scary, but once again, it shows how much you can mistreat DMX512 (through ignorance) and it still works. If I did this, it wouldn't work 'cos I know its wrong... (They have a parallel run of mic cable for the comms so its easy to move both desk and comms in one go) Link to comment Share on other sites More sharing options...
DonkiDonki Posted February 26, 2009 Share Posted February 26, 2009 By the way, the Showtec DMX merge is only about £100, so not a particularly expensive solution. Not as cheap as having a link on-stage to connect into as suggested but it does give you a bit more flexibility. Link to comment Share on other sites More sharing options...
benash Posted February 26, 2009 Share Posted February 26, 2009 If you are trying to keep it cheap I'd be inclined to go for the daisychain method described above. It'll cost you a couple of plugs and a bit of cable... far cheaper than the other options. If you use CAT5 cable it can become very cheap indeed. Link to comment Share on other sites More sharing options...
dth122 Posted February 26, 2009 Author Share Posted February 26, 2009 If you are trying to keep it cheap I'd be inclined to go for the daisychain method described above. It'll cost you a couple of plugs and a bit of cable... far cheaper than the other options. If you use CAT5 cable it can become very cheap indeed. That was the route that I had originally planned to take, but was hoping to get some feedback from others who have done the same thing. My biggest concern is that when I'm controlling from the stage location, there's 150' of cable further down the chain that's unterminated. Do I need to be concerned about noise or any other problems caused by that long run? - Dave Link to comment Share on other sites More sharing options...
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