The huge horn pictured above is one of four giant acoustic orifices at the ESA’s Large European Acoustic Facility in Noordwijk, the Netherlands. Rather than killing humans, though, the horns are actually for testing satellites — to see if they can withstand the noise of a rocket launch. (As you may know, the Space Shuttle’s Mobile Launch Platform used to dump 300,000 gallons of water onto the platform during launch, to absorb the intense acoustic energy that would otherwise damage the Shuttle.) The ESA’s horns are essentially giant air horns, using nitrogen gas to produce sounds as loud as 154 decibels.
The question is, is 154 decibels enough to kill you? In all honesty, probably not — unless, perhaps, you were stuck with your head inside the horn for a prolonged period. 150 decibels is usually considered enough to burst your eardrums, but the threshold for death is usually pegged at around 185-200 dB.
A passenger car driving by at 25 feet is about 60 dB, being next to a jackhammer or lawn mower is around 100 dB, a nearby chainsaw is 120 dB. Generally, 150 dB (eardrum rupture) is only achieved if you stand really close to a jet aircraft during take-off or you’re near an explosive blast.
If you actually wanted to intentionally kill someone with a sonic weapon, there isn’t a whole lot of research on how you would actually go about doing it. The general consensus is that a loud enough sound could cause an air embolism in your lungs, which then travels to your heart and kills you. Alternatively, your lungs might simply burst from the increased air pressure. (Acoustic energy is just waves of varying sound pressure; the higher the energy, the higher the pressure, the louder the sound.) In some cases, where there’s some kind of underlying physical weakness, loud sounds might cause a seizure or heart attack — but there’s very little evidence to suggest this.
Perhaps more significantly, though, it’s important to note that a sonic weapon doesn’t have to be lethal or incredibly loud to be effective. High-intensity ultrasonic sound (generally anything above 20KHz) can cause physical damage. Some very low frequencies (infrasound) can apparently cause your eyeballs to vibrate, making it very hard to see. Targeted “sonic bullets” that cause localized pain (or simply burst your eardrums) is probably enough to immobilize most non-action-hero humans.
So, there you have it: Sound can kill you, but not in the standing-in-front-of-a-giant-speaker-stack-at-a-gig way that you were probably thinking. Unless you’re in an explosive blast (in which case you’d have other concerns, too), or you’re the victim of military testing of sonic weapons, the worst that’ll probably happen is that your eardrums would burst.
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