Q:

How to disable pulseaudio automatic device switch?

My speakers are plugged via optical output. Each time my screen wake up from sleep, pusleaudio automatically switch to HDMI audio where nothing is plugged.
How can I prevent that ?

A:

Let me know if this doesn't work for you and I'll delete my answer. I don't have your speaker system but this should work.
Disable automatic device switching
When signal is lost to during sleep, Pulse Audio is automatically configured to activate the default source (your HDMI). Upon resume the sound device is still on HDMI. To override this setting, tell Pulse Audio to never switch sound devices automatically:

edit the file /etc/pulse/default.pa
find the line load-module module-switch-on-port-available
insert a # at the beginning of the line to disable automatic port switching
save file and exit editor
type pulseaudio -k to reload configuration

