http://fivethirtyeight.com/features/the-loudest-sound-in-the-world-would-kill-you-on-the-spot/

“For instance, the loudest animal on Earth might, in fact, live in the ocean. Sperm whales use echolocation to navigate, similar to what bats use — they make a clicking sound and can figure out what’s around by the way that sound wave bounces off objects and returns to them. A sperm whale’s click is 200 decibels, the unit used to measure the intensity of a sound, said Jennifer Miksis-Olds, associate professor of acoustics at Penn State. To give you a sense of the scale, the loudest sound NASA has ever recorded was the first stage of the Saturn V rocket, which clocked in at 204 decibels.

But the whale is not really as loud as the rocket, she told me. Because water is denser than air, sound in water is measured on a different decibel scale. In air, the sperm whale would still be extremely loud, but significantly less so — 174 decibels. That’s roughly equivalent to the decibel levels measured at the closest barometer, 100 miles away from the Krakatoa eruption, and is loud enough to rupture people’s ear drums. Suffice to say, you probably don’t want to spend a lot of time swimming with the sperm whales.”