Ardour: No audible sound

I've installed Ardour and imported a wav file. I can see the VU meters light up in response to the audio but I can't hear anything.
I'm really not sure where to start looking for a solution. I've already tried every channel in the XFCE4 mixer.

Details:
Arch Linux x86_64
Audio device: nVidia Corporation MCP72XE/MCP72P/MCP78U/MCP78S High Definition Audio (rev a1)
Seen as: HDA NVidia (Alsa Mixer) by the XFCE4 Sound Mixer.

Any help would be really great,
Thanks