If you hot-unplug a USB audio device the links to /dev/audio are broken. As a result, some audio applications might not recognize audio devices, including on-board audio. Rebooting the system or hot-plugging the USB audio device has no effect.
Correct the broken links by typing the following on a command line.
# rm /dev/audio* # /usr/sbin/devfsadm -c audio
For more information see devfsadm(1M).
Third-party USB speakers might not produce sound after the USB driver is attached. Increasing the speaker volume or hot-plugging the device might not have any effect.
Workaround: Power cycle the USB speakers.