As far the definition of Decibel you found it. Sound intensity or volume indeed doubles for roughly each 3dB in SPL which is a mathematical certainty due to the formula.
Nope!
Shadorne. Apparently you have as much of a problem reading as you do listening.
In my 03-04-2018 7:00pm post to which you refer, you can note that this article http://newt.phys.unsw.edu.au/jw/musFAQ.html#add **DOES NOT** include the word "volume" (with respect to doubling every 3db).
You are confusing "intensity" and "volume", believing (incorrectly so) that they are one and the same.