Sorry to necro this old thread in 2020, but wanted to chime in that the info above helped me.

> plasmashell --version
plasmashell 5.18.3

I've been suffering for 2 months now:
* getting an awful bell sound thru earphones.
For example in "open file dialog" from VSCode, pressing "backspace" causes this.

I had had system sounds at 0% for a long time, but this damn bell kept killing my ears.

System sounds set here to be specific: "System Settings" > "Audio" > "Applications" > "Notification Sounds".

Fix was indeed explained in this thread above:
Bell sound is hidden in "System Settings" > "Accessibility" > "Bell":
Disabled "Use system bell" checkbox.
Abled "Use customized bell", and left the "Sound to play" empty.

Thankfully no more killer bell!

Wow, it appears to be VERY hard to disable all notification sounds. Using Plasma 5.25.5 to see if this is something I would like but I cannot find how to disable the top 1 annoyance of every OS I have worked with.

Every tip I've seen I cannot find, as if the UI has been changed over and over again.

I am not going to disable sounds for every event on every application, there should be a global one. I hope someone can show me, otherwise I am going back to xfce. The widgets are nice in plasma but I need some more pros and fewer cons compared to xfce...