USB speakers selectable but not working


I Tried plugging in some JBL Pebbles USB speakers to my raspberry Pi 2 although I could select them in settings -> audio no sound would come out.

As those speakers worked out of the box booting on Raspbian I am suspecting I’m just missing some package.
I’ve tried installing pulseaudio (apt-get install pulseaudio) but this didn’t work.
Can someone help me on what I should look at?