Pulse Audio is another sound server, which is the default sound server under ubuntu since 8.04 Hardy Heron. Also it's usage is recommended after Ubuntu 8.10 Intrepid Ibex. Nearly error free its running since Ubuntu 9.10 Karmic Koala.
Allowing sound to play in the virtual console
In 11.04 the default setup does not allow sound to play when switching out of the xorg GUI, or when logging out of the GUI or stopping the GUI completely.
The solution to allow sound to play outside of the GUI (for use with MPD for example) is to make sure the user is added to the audio, pulseaudio and pulse-control groups ... Applications -> Users and Groups. The console-kit module may also have to be removed from /etc/pulse/default.pa
Restart to enable.
https://help.ubuntu.com/community/UbuntuStudioPreparation#PulseAudio and Jack - Getting Sound from Firefox and alike through Jack for UbuntuStudio.
http://www.pulseaudio.org/ - Homepage of Pulse Audio
http://www.pulseaudio.org/wiki/PerfectSetup -The Perfect Setup of PulseAudio.
http://wiki.ubuntuusers.de/pulseaudio - German article, where I took initial information from.