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I purchased a 27" Cinema Display to go with my late 2009 iMac.

What I would like to do is use the speakers on both displays. This doesn't seem possible using System Prefs -> Sound. I can only set it to use one set of speakers or the other.

Ideally I'd have the cinema display output the left channel while the iMac outputs the right.

Is there a way to use them both?

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May I ask you why you want to do that? Curiosity. –  Martín Marconcini Oct 15 '10 at 5:50
    
Well, now I have 2 nice screens, but it is a little jarring to be watching a video on one of them and have the sound come out of the other. Plus, I figured, why let one set of speakers go to waste? –  Pat Ludwig Oct 15 '10 at 12:14
    
Fair point :) In any case, you can always find some wireless pair of speakers to separate them enough, but that’s always more painful :) –  Martín Marconcini Oct 15 '10 at 19:24
    
There's a reason why the BassJump Speaker requires you to add custom software for it to actually work. I don't think this can be done without external software -> perhaps as much as kernel module hacking. (I don't know what BassJump actually is on the software side, as I don't have one.) –  Jason Salaz Oct 18 '10 at 8:46

2 Answers 2

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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 syncronization 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 reate an aggregate device of your two sources (Display and Headphones) like we did before, then install JackOSX, set it's 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 thing 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.

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Thanks for the suggestions. I'll be experimenting this weekend. –  Pat Ludwig Oct 15 '10 at 19:15
    
I was able to get an aggregate device working...sorta. Now I have the left speaker on the left monitor outputting the left channel, and similarly on the right. Closer to what I want. Unfortunatley, the aggregate sound device is not controlled by my keyboard controls (fn-F10 an the like). I've installed JackOSX but haven't got a chance to experiment. Thanks for the help. –  Pat Ludwig Oct 19 '10 at 17:57
    
@Pat Glad you made it work “sorta” :) Experiment with JackOSX, I’ve had good experiences in the past with other experiments! –  Martín Marconcini Oct 19 '10 at 20:41

Get two sets of external speakers (one for each monitor), and plug them into a Y-splitter cable, and plug that into the Mac. You'll get the sound balance you seek and, unless you are a hardcore audiophile or have perfect hearing, you won't notice the difference between the analog/digital sound and experience better sound overall.

Just because there are speakers on your Apple hardware doesn't mean you have to use them, or to put it another way: two pairs of powered, external, analog speakers will beat the sound of the internal-but-wired-the-same-way-as-external speakers any day.

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I think I'll pass on the 2 sets of speakers, but you make a good argument for one. I was hoping to avoid more cords and clutter on my desk. –  Pat Ludwig Oct 15 '10 at 19:17
    
Sometimes you just gotta do what you gotta do. –  Philip Regan Oct 15 '10 at 19:57

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