A couple of months ago I had the idea to see if there was a simple way to play iTunes music from the built-in iMac speakers while also playing it through a Bluetooth speaker (in this case a JBL speaker). My goal was to have the music playing from the computer in one room and also playing from a Bluetooth speaker in the dining room. Sure enough, OS X has a way to do this (I’m running 10.9 so I don’t know how widely this feature is supported across older versions of OS X).
Thanks to user Eric Ross in the Apple Support Communities I didn’t have to do much searching to find the answer. As detailed in his response, the solution is to open the Audio Midi Setup application located in the Utilities folder and then simply create a Multi-Output Device that has both speaker types selected. Note that in order for this to work the Bluetooth speaker needs to already be connected to the Mac.
At this point we’ve only created the multi-output device. One additional step is required – setting it as the current output device (System Preferences -> Sound -> Output) :
And that should work. The Bluetooth audio (at least with the settings I used) will have a slight delay in comparison to the system speakers. Bluetooth has a relatively short range so the practical applications of this method may be limited by obstructions within one’s home and the receiving capability of the Bluetooth device that is used.