Summing cable XLR (x2) Female to (x1) Male


protect your ears!
One for the cable experts out there!

The idea is to connect 2 audio interfaces to the same monitoring setup using a pair of summing cables that have this configuration:

XLR (x2) Female to XLR (x1) Male.

The setup is:

OUTPUT 1 of both Audio interfaces go to the left speaker
OUTPUT 2 of both Audio interfaces go to the right speaker

Would there be any potential problems or loss of signal strength/quality you might run into?


Senior Member
I think this could be bad. Two separate outputs with different impedence loads to one input. Possibly some type of overload issue? This is where some type of mixer comes in to play to manage that load. I'd have to think it over but my first thought is you will have problems.


my office these days
Nope- you WILL have problems, for the exact reason given above. Outputs are (generally) designed with a very low source impedance, thus they will drag down another low source impedance, making a mess of things (at best) and possibly even damaging one or both outputs stages. (ah for the days of output transformers<G>!)

You do not need a mixer, although that is probably the easiest solution (if you have one.)

Otherwise you can sum the outputs passively or actively. If you want to build this into a cable then passive it is.

There are two, maybe three common configurations...

If you want to handle ANYTHING that is thrown at you put a 10K resistor in series on each signal conductor. This is as close to guaranteed as you can get.

If you know that you are working with outputs that were designed to "pro" standards you can reduce the resistors to 1K (some folks say 470 ohms, that's a little low for my tastes).

And if you end up with an exaggerated low frequency bump you can add a 20K resistor from the junction of the two series resistors to ground, but that is seldom necessary.

Does that answer the question??? Let me know if you need more info...