How do I set the stereo out put of a mix to mono?

My current mix setup is to have Ardour on a Mac Pro as part of Ubuntu Studio (no Mac OS at all). I run the output through the headphone outs to a stereo, and monitor the sound with my stereo speakers: I do not have studio monitors yet.

When I’m mixing, I like to switch to mono output for EQ and compression settings. Right now, I just push the mono/stereo button on the receiver. I read where I can enable the monitor in Ardour. I did that and clicked the ‘mono’ button, but the output was still stereo (the master fader was selected). Is there something else I should do to enable a mono output from already recorded tracks? My interpretation of the manual is that this was for input; is my interpretation correct?

Thanks.

“the master fader was selected” … not quite clear what you mean here.

If you use the monitor section, then you monitors should be connected to its outputs, and the master fader should be routed elsewhere (typically, some other system). Then when you press its “Mono” button, you will hear mono. Listening to the master bus when using the monitor section defeats its purpose (and isn’t what happens by default).