No sound in JuceDemo on OSX



I tried the JuceDemo, it compiles fine, but there is no sound (with the FilePlayback and MIDI i/o sections for example).

I've tried with the 3.1.1 release and with the latest commit on github.

My configuration :

Mac Mini (Mid 2011)

OSX Yosemite 10.10.1

XCode 6.1.1


I saw Audio issues in this forum but it talks about compiling problems, it's not my case since I can run the demo.

I don't know what to check. I've tried OpenFrameworks sound examples and I have sound.