deathangel1479 I've fixed up the delay, changed "Set volume" to "Set master volume", and after set mute off, return to anterior value. Too, now I programmed for the sound plays only when using the Slider Bar (but don't work because Construct 2's HTML elements is on top of layer constantly and don't support touch events as sprites do well).
Here is the updated .capx.
Isn't perfect because the Slider Bar/Percentage are not sensible (have jump between numbers), but is very better now.
You can write a tutorial in your default germany language using this .capx, and I'll translate to english.
Note: I've used the deprecated "Web Storage" plugin to figure the "before_volume", because is very complicated for me to get "Local Storage"'s values. Used a global value because Slider Bar don't accept strings, only numbers...