libao.conf man page doesn't list default_driver=pulse option
This option is especially important for users of Pulse, as they often are unaware they need to switch from 'alsa' to 'pulse' to allow concurrent use of the sound device. See:
https://bugs.launchpad.net/ubuntu/+source/libao/+bug/1075479
https://wiki.archlinux.org/index.php/PulseAudio#libao
https://github.com/PromyLOPh/pianobar/issues/494
Will attach patch shortly