How to mute sound effects in 14.04 via the command line?

Using the command line, I want to mute the sound effects in Ubuntu 14.04.

The GUI way of doing so is going to System Settings (unity-control-center), then going to the Sound Effects tab:

The answer to this question outlines a way to do so using gconf (sudo su gdm -c "gconftool-2 --set /desktop/gnome/sound/event_sounds --type bool false"), but that no longer works in newer versions of Ubuntu.

I also looked for a clue at the output of pacmd info, but couldn't find anything useful either.

There is what seems to be a relevent setting that can be changed in dconf (org/gnome/desktop/sound/event-sounds), but it is set to false and changes nothing. There are some Ubuntu settings, especially for Unity, that don't have visible dconf settings. Still, they can be seen when changed with a GUI while running dconf watch /. But it shows nothing when muting/un-muting that setting.

I know I could just remove all the sound effects, but there must be a proper way of doing this...

It's a bug and you need to report it. I test that on Ubuntu-Tweak tool and capturing by dconf watch / it's capturing correctly but I see no changes from default sound settings, it's still don't change to Mute.

see the screen shot: if I turn off it:

And if I turn on:

And as you see the default path is correct(org/gnome/desktop/sound/event-sounds), but the changes not take any effect on turning off/mute the "Sound Effects" and in both state I have no changes. I also tested it by rebooting system but no luck.

So it's a bug.