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Thread: A really stupid question

  1. #1
    Resident Antagonist Benny Smyth's Avatar
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    Default A really stupid question

    Recently, I had had an issue with my primary playout. First time in 18 years, but it's made me ponder about what to do going forward.

    As is standard, I have two laptops that are exact mirror images of each other - both have Traktor with updated library and both have MyDMX. Every night, one will run MyDMX and the other Traktor. I have two S4 Kontrollers set up so should option A fail me, then I move over to option B. The problem is that I don't use a mixer to plug into, so for the one issue I've had, I had to pull the output from one S4 to the other. Took mere seconds, but it felt like a millennia!

    I'm not a fan of having a mixer as it'll add another minute or so to my setup and takedown (and if you're thinking "So what?", then you're not like me who spends ages working out how to shave seconds here and there), plus the sort of person that I am will have a Xone:43 or something of a similar ilk.

    So, to avoid the extra expense of a mixer, can anyone tell me why having an XLR splitter plugged into the speaker, with both the primary and secondary playouts plugged in wouldn't work?

    To me, it looks like it would do the job but I just want to make sure that I'm not overlooking something.

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    Dinosaur Excalibur's Avatar
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    Well the short answer is because you're not splitting, you're joining. And yes, I know I'm splitting ( hairs ) but behind the whimsy, there's the reason.

    Splitter cables are simple ones, but joiners should have resistors in to ensure safety, as you may damage one component, but I'm not well enough up on it to say what size of resistor or other component. We've had this discussion elsewhere, on another forum. Not to say I haven't done something similar myself without problems, but just because I got away with it, doesn't mean you will.

    Hopefully, the technocrats will be along shortly to explain. What would I recommend? Well the easiest one would be a switching box, which is exactly what its name implies. Problem with that would be the almighty thump through the PA as you press the switches.

    Top of my head, nothing springs to mind. Mixer isn't the best option, simply because it's duplication of components. Sorry I haven't helped much.
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    Ezekiel 25:17 funkymook's Avatar
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    It might be stating the obvious but if your speakers have a second input just have another run of xlr cables going into that from your back-up.

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    MDD Supporter Imagine's Avatar
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    Quote Originally Posted by funkymook View Post
    It might be stating the obvious but if your speakers have a second input just have another run of xlr cables going into that from your back-up.
    ^^^ What he said, although it increases set up time.

    I used to worry like that (there's a post on here somewhere about it and indeed I did purchase a splitter thingy....which actually had the effect of dampening the signal somehow).

    I still carry spares of everything, but I'm not that paranoid these days. If there's 30 seconds of dead air then so-be-it. I have the backup and knowhow to get out of it and the party will continue.

    Not ideal, but talking to several other operators in these here parts recently who I thought worked in the same sort of way as me....if something of theirs dies (including laptop or mixer) - the party's effectively over! They can't afford/don't want to store the spare kit

    Now THAT is a way I'd NEVER feel comfortable working with.

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    MDD Supporter Nakatomi's Avatar
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    Blah blah output impedance blah blah input impedance..

    Or in laymans terms...

    Ye cannae just combine mixer outputs into one cap'n or she's gonna blow.

    Better to use a passive or active combiner/mixer. With passive yay no power needed & very little can go wrong but... You lose some signal level.

    Active combiners/mixers won't incur any signal loss (ideally) but need power.. And then they're just another thing that can go wrong.

    For my money I'd prefer to take the hit of a few seconds of dead air when something goes wrong than increased setup & teardown time.

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    MDD Supporter Nakatomi's Avatar
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    The technical explanation of why you shouldn't just combine the outputs of audio devices is this :

    The output impedance of a mixer or other playout device is generally quite low, say around 150 ohms. This is designed to plug into an input which might have an input impedance (in most pro kit) of around 600 ohms or 1000 ohms or more.

    Plugging one output into another, you're potentially halving its drive capability (voltage level and headroom before distortion) because 150 ohms in parallel with 150 ohms is 75 ohms. This would mean the output stage of each device would have to work twice as hard as usual. They may cope, or they may not. They may be damaged but best case performance will likely suffer.

    Passive (unpowered) combiners will use either transformers (slightly lossy but expensive ) or resistors in line to sum the signals (more lossy but much cheaper & less bulky than transformers).

    Some kit, it's unknown which, you can likely get away with joining outputs of til the cows come home. That's usually real pro stuff like what they use in radio & telly though (where it's still analogue signals anyway). I remember reading sonifex cart machines' outputs were designed to be connected across others so a cart machine stack would only need one stereo pair of mixer inputs.

  7. #7
    Ezekiel 25:17 funkymook's Avatar
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    Quote Originally Posted by Nakatomi View Post
    The technical explanation of why you shouldn't just combine the outputs of audio devices is this :

    The output impedance of a mixer or other playout device is generally quite low, say around 150 ohms. This is designed to plug into an input which might have an input impedance (in most pro kit) of around 600 ohms or 1000 ohms or more.

    Plugging one output into another, you're potentially halving its drive capability (voltage level and headroom before distortion) because 150 ohms in parallel with 150 ohms is 75 ohms. This would mean the output stage of each device would have to work twice as hard as usual. They may cope, or they may not. They may be damaged but best case performance will likely suffer.

    Passive (unpowered) combiners will use either transformers (slightly lossy but expensive ) or resistors in line to sum the signals (more lossy but much cheaper & less bulky than transformers).

    Some kit, it's unknown which, you can likely get away with joining outputs of til the cows come home. That's usually real pro stuff like what they use in radio & telly though (where it's still analogue signals anyway). I remember reading sonifex cart machines' outputs were designed to be connected across others so a cart machine stack would only need one stereo pair of mixer inputs.
    Does that still apply when only one output is being used at a time? That wouldn’t be summing two signals would it? (as would be the case if you have to switch to your back-up).

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    Quote Originally Posted by Imagine View Post

    I still carry spares of everything, but I'm not that paranoid these days. If there's 30 seconds of dead air then so-be-it. I have the backup and knowhow to get out of it and the party will continue.
    I am the same now after many years of having secondary playout etc all wired in ready to go.
    Nowadays I have backup mixer etc in the van, second laptop in a case with me. Should there be a bit silence I am sure nobody is REALLY going to complain if you explain the situation and get up and running with minimal fuss.
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    Ezekiel 25:17 funkymook's Avatar
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    Quote Originally Posted by ppentertainments View Post
    I am the same now after many years of having secondary playout etc all wired in ready to go.
    Nowadays I have backup mixer etc in the van, second laptop in a case with me. Should there be a bit silence I am sure nobody is REALLY going to complain if you explain the situation and get up and running with minimal fuss.
    Unless it’s the first dance or other key moment...

  10. #10
    MDD Supporter Nakatomi's Avatar
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    Quote Originally Posted by funkymook View Post
    Does that still apply when only one output is being used at a time? That wouldn’t be summing two signals would it? (as would be the case if you have to switch to your back-up).
    If one is powered off, then maybe not but it depends on the makeup of its guts. Otherwise yes.

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