New answers tagged speakers
Quit the coreaudio task in Activity Monitor.
If you want now in 2015 there's an extra step that allows you to send audio to multiple devices through your macbook. http://weblog.rogueamoeba.com/2012/02/12/send-audio-from-ios-to-multiple-speakers-with-airfoil/ Meaning iPhone to mac, mac to multiple devices.
I've seen that image when I plugged in a hdmi monitor that didn't have any speakers on it. My computer switched to hdmi audio out and there wasn't anything to output the audio. If you are using an external hdmi monitor like that, go to: System Preferences > Sound > Output and select your speakers.
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