The awesome power of sound


This is copied from a Reddit post by kerrigan7782 – normally I would just link to external sites but I don’t know if Reddit posts are deleted after a certain amount of time. The text is about the sound being emitted during the take-off of a space rocket.

The Saturn V itself, (and all large rockets nowadays) are so loud that they will kill themselves from volume alone. NASA must employ a Sound Suppression System that dumps enormous quantities of water continuously onto the launch pad to muffle the sound waves reflecting off the launch pad surface as they are so powerful that they will damage the rocket itself.

This video shows the system test firing, gets into full gear around :37 seconds in.

Now then, lets do the math, this chart handily informs us that the Saturn V rocket produced a SWL (Sound Power Level) of about 220 decibels, which is sufficient to melt concrete nearby and set grass aflame a mile away, however, lets just look at sound attenuation calculations alone and compare them to smaller figures to make it seem more comprehend able.

Since I am not a physicist or engineer (yet) I am going to use the simplified math that direct sound attenuates at a rate of 6 dB each time you double the distance. Since I am lazy I am going to go one step further and use this site’s calculator to convert SWL to SPL.

At 20 meters from the rocket nozzle an observer might be experiencing 182 db SPL, the equivalent of more than a pound of TNT detonating 15 feet away or 1 ton of tnt detonating 150 feet away, survival would be extremely unlikely, wind force would be over 100 mph, buildings would be torn apart, it would become very, very hot from the sound pressure alone compressing the air.

At 100 meters it would fade to (merely) 170 db, you would be unable to breathe or likely see at all from the sound pressure, glass would shatter, fog would be generated as the water in the air dropped out of suspension in the pressure waves, your house at this distance would have a roughly 50% chance of being torn apart from sound pressure alone. Military stun grenades reach this volume for a split second… if they are placed up to your face. Survival chance from sound alone, minimal, you would certainly experience permanent deafness but probably also organ damage. At this distance, the ambient air temperature would remain relatively steady, with perhaps a little heating or cooling, (alternatively it might alternate between hot and cold as the low frequency vibrations pass over you)

At 500 meters, 155 db you would experience painful, violent shaking in your entire body, you would feel compressed, as though deep underwater. Your vision would blur, breathing would be very difficult, your eardrums are obviously a lost cause, even with advanced active noise cancelling protection you could experience permanent damage. This is the sort of sound level aircraft mechanics sometimes experience for short periods of time. Almost twice as “loud” as putting your ear up to the exhaust of a formula 1 car. The air temperature would drop significantly, perhaps 10-25 degrees F, becoming suddenly cold because of the air being so violently stretched and moved.

At 2 kilometers (140+ db), you are reaching the closest you could be without near instant permanent hearing loss without hearing protection. You would feel a similar amount of force from the sound pressure as a football player tackling you. Your throat and vocal cords would start vibrating along to the sound of their own accord. The air temperature would drop “only” a few degrees from expansion.

At 5 km, or 3 miles (135 db) it would have a similar volume as a freight train horn continuously blowing in your near proximity, but low and rumbling. Permanent hearing damage would result without significant hearing protection.

NASA actually lets people view the shuttle launch at a distance of around 7 miles (front seat of rock concert-esque volumes predicted here, freaking casuals). I should also mention that this is a very simplified model that ignores wind speed, humidity, altitude, the existence of the ground, everything to do with the source of the sound (like superhot rocket exhaust) and some other factors.

And at last, I leave you with one of my favorite videos in the world. (turn it up, a lot)

 

 


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