If you're using OS X's built-in AirPlay support, you might need to up the volume for the AirPlay speakers when you start streaming. Here's how you do that:
- Open the System Preferences window;
- Select Sound from the list;
- Select the Output tab and select the AirPlay speaker you'd like to stream to from the list (type should say "AirPlay");
- Now, just drag the volume slider:
- Afterwards don't forget to switch back to your Internal Speakers;
- Use AirVLC to start streaming!