Disable KDE 4.7 system sounds

In KDE 4.10.5, you can disable all system sounds without muting all media.

System Settings > Common Appearance and Behaviour > Application and System Notifications > Manage Notifications > Player Settings > No audio output.

Also, you may disable Event Sounds: left click the sound tray icon and slide down the Event Sounds slider or completely mute it.

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In KDE Plasma 5, you can left-click the kmix (volume) plasmoid, and turn down "Event Sounds", similarly to the screenshot above.

If this doesn't work, you can turn off the sounds for each notification class individually, in System Settings > Notifications. Cycle through Event source, looking for entries with the Play a sound icon associated with the entry, then toggle off Play a sound.

Try either:

System Settings -> Notifications -> Player Settings\

Then choose "No audio output."

or:

System settings -> General -> Notifications -> System notifications -> Applications -> Event source

Then choose"KDE System Notifications"

There is a longstanding bug in KDE to disable sounds for all apps. I suggest commenting on that bug.