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:
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.