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I know this is going to sound like a really stupid question, but here it goes...

I have dual mono 1/4" jacks for the main output from my soundboard. I currently, only have the left side being sent to the amplifier for the auditorium speakers. I'd like to have both left and right sides mixed into a single mono signal to then send to the speakers. In my past, I'd just use a simple mono-to-stereo splitter adapter backwards. For instance, I'd just use an adapter that looks like this one:

Example Mono-to-stereo Splitter Adapter (Hosa YPP136)

But I worry that hooking it up that way isn't really the "right" way to do it. If there's no problem with doing it that way, I'm all for it, but if there's better, recommended way to combine stereo into a single mono line, I'd love to know what that is.

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Well, as you've noticed yourself, it will normally work. This is because both channel outputs should be expected to have the same output impedance, so wiring them parallel effectively creates an averaging circuit. However, this is not really an intended mode of operation.

  • The output impedance of this combined output will be half the individual impedance, which generally won't matter at all.
  • More problematic is that for strong side-components in the signal, the outputs perceive essentially a total short circuit. If the outputs have particularly low impedance (like headphone outputs), this can drain significant amounts of current, but again unlikely to be an issue except for battery-powered operation.
  • Finally, if the impedances do not quite match (output impedance is normally not something that needs to be calibrated precisely) then the stereo balance will be off in favour of the channel with lower impedance. This is still probably harmless, unless you're dealing with complex wide-stereo material.

Nevertheless, the "right" way would probably to mix in mono right in your soundboard, and route out only one single channel. But if that isn't possible for some reason, I'd just stick to the Y-cable hack. Of course, you can always use a small dedicated mixing console for the task, but probably you wouldn't really notice the difference.

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  • Thanks. The soundboard has a bunch of mono inputs and then it has a few stereo inputs (one slider for both channels). We currently aren't using the stereo inputs for anything (probably for this reason). We have a CD player going into two separate mono inputs. I'd like to move the CD player to one of the stereo inputs and free up those two mono inputs for mics. But when I do that, only the one side of the CD comes through. I'll have to do some reading in the soundboard manual, but from what I can see, there's no option that would mix the two channels before going to the main.
    – Steven Doggart
    Jan 19, 2015 at 14:05
  • You can plug the CD player in both L-inputs of two stereo channels.
    – leftaroundabout
    Jan 19, 2015 at 14:14
  • Well, I need to be able to pan from one channel to the other. For instance, if it's a split track CD, I need to be able to play just the music without the vocals, etc.
    – Steven Doggart
    Jan 19, 2015 at 14:16
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    Well... if you're balancing between two channels of a CD then I'd say you should particularly use two seperate channels. It's not really the point of stereo controls to do that kind of thing.
    – leftaroundabout
    Jan 19, 2015 at 14:27
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    It just seems a pretty strange requirement to me. I would ditch those two-channel CDs and instead play mono tracks right from a laptop/taplet/smartphone. Gives you much more control.
    – leftaroundabout
    Jan 19, 2015 at 14:41

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