Loudest Sound Ever?

 The Big Bang...

Krakatoa?  I think Vesuvius.

dweller3, indeed!
And going the other way, from Discovery.com
"It may be possible to destroy everything with a loud enough sound. NASA estimates the mass energy of the universe at 4x1069 joules. But that number is considerably smaller than the energy created by 1,100 decibels of sound."

I went to a deep purple concert thst was on average over 105db 
my ears buzzed for 2 days ,Burn concert tour 

I saw twin V12 2 stroke Detroit on fuel, Blower, fed by a pair of BIG turbos at the tractor pulls. There was a couple of Cats and John Deere too. The big cat was 4 stroke, you felt it 1/4 mile away no problem.

But that Detroit with open exhaust I don't see how the operator could stand it. I sure couldn't. There was so many noise complaints, that never happed again.. LOL

Made a Merlin gas engine sound like a toy.. and they are loud too with open headers.