Hit the Windows key on your keyboard and type: Sound
Once inside the Sound window, you will see four tabs. Make sure the Playback tab is the one selected.
There we will find the speakers/headsets connected to the computer. Next we need to Right Click the speakers/headset we are wanting to use and select Set as Default Communication Device and Set as Default Device.
Once we get that set, lets go ahead and restart Virbela and try talking to someone in world. There should be a speech bubble over the avatars head when talking.