Here’s the Loudest Possible Sound Our Puny Atmosphere Can Handle

Lots of entities like to lay claim to loudness as their personality: rock bands, roaring animals, your upstairs neighbors using a vacuum that sounds like the Department of Defense engineered it. As long as you have made the mentally taxing choice to live in a major city, your eardrums are also under attack by any number of dins and rackets throughout the day. It’s a powerful thing, too, with sound being able to cause pain and impede human function, as the aforementioned Department of Defense knows well.

You don’t even have to exit the realm of fairly common items and events to start getting into dangerously loud levels. Anything over 140 decibels is enough to cause immediate pain and hearing damage, which is why everybody in John Wick would have horrible tinnitus, but I guess assassins do look less cool in earmuffs. Gunshots clock in in the 160-decibel range. Ambulance sirens are around 130 decibels.

If you’re curious enough to start looking into the upper limits and the loudest sounds of all time, however, you’re going to end up with a very anticlimactic number: 194 decibels. It doesn’t seem to make sense on its face. For example, the loudest sound in history, the eruption of Krakatoa in 1883, was recorded at 170 decibels, 100 miles away. Obviously, you’d think that if you were only a mile away, it would be way past the 194 decibel threshold. In strict scientific terms, though, even that eruption never made a sound louder than 194 decibels.

This is because the 194 decibel maximum doesn’t come from the human ear, or recording instruments, or limitations of a scale, it comes from the literal limitations of sound. Let me explain: Sound is pressure from a vibrating object passing through a medium, in this case air (water actually has a higher limit, at around 270 decibels). When that vibration hits an eardrum or robot equivalent, it’s registered as sound. At 194 decibels, the low pressure regions of that wave have zero molecules, making it a bit like absolute zero in sound terms.

Does this mean you’d be surprisingly fine if you were close to Krakatoa? Oh hell no. Sound stops being technically “sound” at 194 decibels, but it doesn’t stop existing: It just has so much energy that it now carries the air along with it, and becomes a shockwave. If you think of sound as a train, in a quaint and probably flawed analogy, it’s not limited just by how fast the train itself can travel, but by the limitations of the medium it travels on: the rails. If a train goes so fast it rips up the rails beneath it and starts tumbling as a mass of metal, gravel and flying luggage, you might not see it and go, “Wow, that’s a really fast train,” but you definitely still have a problem.

Historically loud sounds may still have an estimated decibel value, but it’s detached from what we consider “sound,” and usually comes from barometer measurements of pressure. If you were close enough to a sound anywhere near the scale of Krakatoa’s eruption, like the ship Norham Castle, 40 miles away, the only thing you’d “hear” was a shockwave rupturing your eardrum.