Here's a discussion we had on IRC about it :

Modulo5k	https://www.allegro.cc/forums/thread/617970 any lubuntu freaks out there? al_install_audio fails
alledos	al_install_audio failing after lubuntu update
elias	? google lubuntu
alledos	https://lubuntu.net/ - lubuntu – lightweight, fast, easier
elias	doesn't say that sound would be different than on normal ubuntu
elias	(which does work)
elias	I'd double check the pulseaudio configuration
elias	if you ever modified it in any way, even several years ago...
elias	then the only solution is to completely wipe the disk and re-install
elias	pulseaudio is one of the modern linux components
elias	and they are like that
Modulo5k	would you mind telling him that? I don't know JACK about ALSA
elias	but basically, try with a clean, unmodified lubuntu first
elias	me neither
elias	
elias	oh, didn't see the link
elias	hm, my first question would be, does anything else play sound on his system
elias	because it sounds like the "default" device cannot be opened, so likely nothing can play sound
Modulo5k	what if the default device was changed by the distro update
elias	then nothing could play sound, not just allegro
Modulo5k	I know how WMP likes to change things every time it updates, and how Windows likes to reset certain security settings 
elias	but yeah, if sound works in SDL apps but not Allegro, we'd want to investigate
elias	otherwise it's just a linux sound question, not Allegro related
Modulo5k	no but al_install_audio is failing, so its an allegro question because it was after an update (and before it worked)
Modulo5k	well could be either
elias	yeah, my guess is all sound stopped working on his system

Hey guys, thanks for your replies. Audio is otherwise working fine on this system, and I have not made any changes to config files or anything else related to audio.

Thanks for the suggestion Elias, but it did not change anything.

I'm thinking I may just install standard Ubuntu, or another distro that has precompiled Allegro files.

Thanks again.

Just a standard 'bare' installation. I did install allegro the way you mention as building complex things like this is beyond my current knowledge.

edit: This error is also in standard Ubuntu 19.10

edit edit: I've reinstalled 19.04 and all is good. Meh.. Thanks for looking into it though.

I just realized I gave you wrong instructions - it's allegro5.cfg not allegro.cfg. The four possible files are listed here: https://liballeg.org/a5docs/trunk/system.html#al_get_system_config

Can you try again with the correct name?

I downloaded Lubuntu 19.10 and I will be testing this soon.

I successfully built Allegro 5 and tested the audio examples in Lubuntu 19.10 in a VBOX VM. They all worked as expected. An error was generated, but playback was not stopped.

GLib-GIO-CRITICAL **: g_dbus_proxy_new: assertion 'G_IS_DBUS_CONNECTION (connection)' failed.