I am setting up a speaker in a courtroom and hooking that to my MacBook Pro, to play Quicktime files, audio files, Windows Media files, and editing I've done on FCP.
I brought a mini stereo Monster cable to two RCAs to plug into my mixer. Does that sound right? Then from this mixer I sent all to the right channel and send that mono signal to the one speaker via a 1/4'' connector attached to an XLR cable.
I am getting a little buzz, and I can't track down the source.
Yes. I need to lose a few pounds, but enough about me. :)
Buzz can be from local sources; light dimmers or other things like ground loops.
Are you hearing the buzz at the Behringer mixer headphone output? If not the problem is after the mixer. Unplug the output from the mixer to the speaker and see if it changes. If you have buzz without the mixer connected to the speaker, the source of the buzz is before the speaker.
Buzz can be from using the unbalanced stereo output from your Mac.
If the problem is there, you can get a small two channel isolation transformer. I use one between my Mac and my rack of gear to stop the buzz.
Can I assume you have a powered speaker? If so, try plugging all power plugs into the same electrical output as the mixer. This will reduce the possibility that a ground loop is the cause of the buzz.
Simple things; Make sure audio lines are not running parallel to power cables.