benweblight Posted January 24, 2004 Posted January 24, 2004 Just wandering, could you send sound (line or speaker) down a 3pin DMX cable?. Mainly just a general question, but also want to test it out with my new cable (500v tested DMX, 3pin neutriks ends, slx stuff).
gareth Posted January 24, 2004 Posted January 24, 2004 No reason why not, as long as we're just talking about low leve (mic/line) signals. But if a cable has 3-pin connectors on the end, it's not strictly DMX cable. Any equipment which uses 3-pin instead of 5-pin doesn't conform to the USITT DMX512/1990 standard. Out of interest, why do you have 3-pin data cable - do you use a lot of Martin moving lights?
benweblight Posted January 24, 2004 Author Posted January 24, 2004 no alot of budget control gear, but martin use 3pin too, suprisingly
TonyMitchell Posted January 24, 2004 Posted January 24, 2004 Just wandering, could you send sound (line or speaker) down a 3pin DMX cable?. pre-amplified sound yes, i.e. between control equipment,but speaker no
Matt Posted January 25, 2004 Posted January 25, 2004 I wouldnt have said that was strictly true tony... if you have speaker cable connected to the XLR's it should be ok up to a certain powered system...?
Shaun Foster Posted January 25, 2004 Posted January 25, 2004 I think he was meaning using the data cable for speakers. This might work with some HiFi speakers, but I'm guessing most PA speakers would use far too much current for data cable. I could be wrong though.
samrennie Posted February 3, 2004 Posted February 3, 2004 careful because if u send any anplified signal it is just a matter of time (depending on the power of the signal) before the cable melts, usually just before or during a show! It is effectively sending 240v mains down a guitar lead, things will go bang! Sam
robloxley Posted February 4, 2004 Posted February 4, 2004 It is effectively sending 240v mains down a guitar lead, things will go bang!Speaker level is more like 50V RMS max. Even 100V lines are only 100V... DMX cable may be rated for 500V - especially install cable so it can be put in the mains trunking - so the insulation won't breakdown, as you said it's the current-carrying capacity that's the problem.
london sound Posted February 5, 2004 Posted February 5, 2004 First why do you want send audio down DMX cable? if I's just to check it's continuity then why not use a cable tester or meter, if as a replacement audio cable then the impedence and or capacitence may be wrong. The suggestion above that the cable is rated to 500v so that it can be installed next to mains cable is completly wrong, the 500v is the max voltage that can be put done the cable before the insulation will start to break down, what governs weather any two types of cable can be installed next to each other is the actual opperating voltage in the cable For instance if DMX operated at 240v then it could be installed in conduit or trunking with 240v mains, however as it operates at low voltage (about 10v I believe) then if installed in trunking it must be in a seperate channel with a physical barrier.DMX can be installed next to microphone, speaker or even telecoms cable, as long as it is screened cable. Please check IEE regs if not sure, I suggest also you consult a qualified electrician about any cable installation. I know that generally with sound we are dealing with fairly low voltages, however an amplifier working flat out supplying bass bins can delivery fairly high voltages and high currents. Please be careful and treat every unknown cable as being potentially live!!! Ian
Ellis Posted February 5, 2004 Posted February 5, 2004 ... then if installed in trunking it must be in a seperate channel with a physical barrier.I think you might be slightly wrong there. The 500v rating on DMX cable is the rating of the insulation on the outer insulation. Low voltage control signals can be routed with high voltage wiring providing the insulation on the control cable is sufficient to protect the low voltage conductors from the high voltages. (I have seen examples of this in theatre and heavy industry - both installed/built by very reputable companes). The insulation between the conductors in the DMX cable is unlikely to be anywhere near that rating and the conductrs will handle only small currents, so the use for anything other than mic or line-level signals is probably best avoided. You will also find that DMX cable has a characteristic impedance suited to an RS485 transmission line, which is not the same as the 600ohm transmission line that a balanced XLR cable is part of. Over short runs, this will probably be inaudible, but over longer runs reflections and losses at different frequencies will degrade the clarity of the signal.
Brian Posted February 5, 2004 Posted February 5, 2004 which is not the same as the 600ohm transmission line that a balanced XLR cable is part of.It's very rare to find true 600 Ohm balanced cicuits these days. BT still use them on local end copper pairs but that's about it. Most (All?) audio desks have an input impedance of around 10k on the Mic input. Most Mic cable is around 100-150 Ohms impedance. These days there is no point in running 600 Ohm circuits, reflections are not an issue in audio circuits and you usually need to transfer the maximum possible voltage, you don't worry about power transfer. For example, the wavelenght of a 20kHz signal is 10km in a typical cable.
london sound Posted February 5, 2004 Posted February 5, 2004 The reason for not running low voltage with high besides the insulation is a condition called inductance. In long runs and where cables get wrapped around each other it is possible for a higher voltage to be inducted to the low voltage cable (ie: transformers) therefore compromissing the low voltage circuit.IEE regs are very clear about mixing types of cable/circuit in conduits and trunking. I know that we all do mixed runs on temporary installations. Ian ps for further info please check IEE Regulations. If you do not know what these are you should not be messing with electricity!!!!
Brian Posted February 5, 2004 Posted February 5, 2004 IEE regs are very clear about mixing types of cable/circuit in conduits and trunking. Reg 528-01-05Where a common conduit...is used to contain category 1 (mains) and category 2 circuits (telecomms/data), all cables of category 1 circuits shall be effectively partitioned from the cables of category 2 circuits or alternatively the latter cables shall be insulated in accordance with the requirements for the highest voltage present in the category 1 circuits. Reg 582-01-07In conduit...where controls or outlets for category 1 and category 2 circuits are mounted in a common box...the cables and connections of the two categories shall be segregated by a parition, which if metal, shall be earthed.
london sound Posted February 5, 2004 Posted February 5, 2004 Thanks , I was not having a go at you Brian, but merely trying to point out to one or two others the necessity to do the job properly. Ian
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