There is no such thing as a default output device (or sink) in PulseAudio. It say so right there in the official documentation. There is something referred to as a fallback device which is used “if the stream has not been seen before”. Yet there is a configuration command called
So where does that leave the user who wants a default device persistent across boots? The answer is: With a few challenges to climb, the greatest probably being insufficient documentation. Sadly people seem to prefer griping about PulseAudio to tipping in and producing good docs.
In the name of documentation (and SCIENCE!) I have tried to test a few of the availabe and potentially default-relevant PulseAudio settings ro see if I could get a surefire way for new streams to always play on the device I want them to. Here’s what I’ve come up with.