audiodisplayimac
I have a dual monitor setup (iMac + Thunderbolt Display). The System Preferences > Sound > Output setup only allows me to choose between one or the other monitor. This causes the sound to come only from left or right side.
Any way to get both monitors to play audio simultaneously?
I don’t know if you can get away with that, but I do know what you can’t do with “the tools you have”.
The first approach would be to - having both output devices connected – create an Aggregate device that encompasses both.
Let’s say one device is called: Headphones and the other is Display.
The initial approach would be to create the Aggregate device in your Audio MIDI Setup panel, add Headphones and Display as devices, mute Headphones’ left channel and then Display’s right channel. Then happily select this new Aggregate device as your sound output and be super happy.
Sadly that doesn’t work. (I’ve tried it). Apparently the clock synchronization between the “devices” doesn’t happen and OS X doesn’t really care, therefore only one device outputs audio. (Sad, but true).
(more information on how to create an Aggregate device that can be found on this Apple Article)
What to do?
There’s hope, but I haven’t tried this solution.
The idea would be to create an aggregate device of your two sources (Display and Headphones) like we did before, then install JackOSX, set its preference to your new aggregate device, start the Jack’s router, set AudioMIDI Setup to use Jack for I/O, open an app to play your music and connect its output send channels to whatever system playback channels you want in Jack Connection manager.
That might work and I suggest you give it a shot.
More simple solutions, might involve cabling, Y-Splitters and weird things which I don’t think you want to dive into (specially given that all the audio is Digital and internal, you’re not talking about external speakers per se).
Finally, although it doesn’t provide simultaneous playback, changing sound sources is very simple with a free utility like SoundSource from your menu bar. (I do it all the time to switch from headphones to speakers).
Hope something of this makes sense.
Both displays show up as audio input and output devices on your Mac and you can pick one or the other to route audio in to from applications. You might be able to create an aggregate device out of them and use them as a four channel output source, but that would not turn out well sonically speaking. You can see it here.
Best Answer
You should be able to use the Audio MIDI Utility (a.k.a. Audio MIDI Setup on Mountain Lion) to create an Aggregate device to mix both output destinations into one item the OS can select.
The Help topics in OSX around this area are...
Play audio through multiple output devices at once
Combine audio devices to use a single device