How loud is the loudest sound ever recorded?

Question

How loud is the loudest sound ever recorded

Answer 1

The explosion of  Mount Tambora, on Sumbawa island, Indonesia in 1815 was heard clearly 2,600 km (1,600 mi) away and has been called the loudest sound ever heard by humans.

It had roughly four times the energy of the 1883 Krakatoa eruption.

The shock waves circled the globe several times but this part might not be considered a “sound”.

Answer 2

I don't know that anyone recorded it or how many dB it was at the source, but the explosion of Krakatoa in 1883 (I think) was heard many miles away.

Answer 3

Well, don't forget that loudness in terms of decibels is relative to your distance to the sound source.  So if I hear an explosion from thousands of miles away, it might be very quiet when I hear it but it might contain a lot of absolute energy at the source.  In that case, the loudest sounds ever heard or recorded probably would be from the big volcano eruptions (though I don't know if they were "recorded").  

But if you're talking about sound in decibels at the recording source, it's a different story.  The loudest sound possible in air is 194 decibels.  What does this mean?  It means that anything with a higher energy density cannot travel as a sinusoidal wave through air--the wave breaks down, causing turbulence and friction at the wavefront (like comparing smooth ocean waves to the breakers on a beach that happen when a wave gets too big).  Such energy in air would turn into heat and even possibly light or plasma rather than sound; it only turns into sound under 194 decibels.  You could imagine that in the first split second of a nuclear blast, the fireball has an energy density greater than the equivalent of 194 decibels, and instead of "sound" you get instant supersonic wavefront of destruction.  Once the energy density breaks down, the shockwave travels out at the speed of sound, starting at 194 decibels and getting quieter as it radiates outwards.  Probably the people who live to tell about nuclear blasts have heard sounds in the lower 100s of decibels or less.  Recording equipement and ears actually get destroyed at sounds lower than 194dB, for example supposedly your hearing tissue gets destroyed pretty instantly at 180 decibels, and even 150 decibels will make you go deaf in a short while.  

So: loudest absolute sound is some sort of cataclysmic explosion volcano, meteor impact, big bang, etc.  Loudest sound in energy density is 194dB and occurs at the edge of destructive events, such as major explosions, suicidal blue whales, supersonic aircraft, etc, but this sound is not heard or recorded by the observer; it diffuses by the time it is heard or else it kills the listener.

Answer 4

The Hyperspike HS-60, invented by Curt Graber of Wattre Corporation, USA, is an Acoustic Hailing Device (AHD) emitter capable of producing a coherent beam of sound, like a laser in the human voice range. In certified field tests conducted in March 2007 its coherent beam length was measured at 264m. and output was measured at 140.2 db at 128 meters range, using less than 3Kw of electricity. Its output is equivalent to 182 dB 1m from the source and, under optimal conditions it can transmit audible voice communications to a target over a distance of more than 3km (2 miles).