Gtk.Settings:gtk-sound-theme-name

"gtk-sound-theme-name"             String                : Read / Write

The XDG sound theme to use for event sounds.

See the <ulink url="http://www.freedesktop.org/wiki/Specifications/sound-theme-spec">Sound Theme spec</ulink> for more information on event sounds and sound themes.

GTK+ itself does not support event sounds, you have to use a loadable module like the one that comes with libcanberra.

Since 2.14