Why does sound past a certain volume become shockwaves?
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It doesn’t.
A shockwave isn’t sound past a certain volume, it’s a pressure wave caused by extreme changes in pressure over a short period of time.
If you detonate a stick of dynamite, it releases gas at an insanely fast rate with deadly force. That blast of pressure radiates outward damaging/destroying things in the near vicinity. The pressure travels through the air, which we hear as the sound of that force.
Contrast that with tapping a coin on a desk. You’re also creating pressure but not a lot – and yet the sound of impact can be quite loud without any dangerous pressure being created.
Because it’s strong enough.
Think of a wave of water on a beach. Every wave represents a sound wave. Every wave can change something on the beach. And if it’s just a grain of sand.
If it can tear down a sand castle, it is a strong wave, right? With much force. Either a lot of water is moved or a little water with enough speed. It could be compared to a shockwave.
Sound is just a pressure wave moving through air. It causes the pressure to fluctuate up and down around the normal level and that’s what you hear, but there’s a limit to how low it can go.
All sound metrics are defined in Pascals so we’ll use those. Normal air pressure is about 100,000 Pascals at sea level. A 120 dB sound makes it go between 99,980 and 100,020. A 160 dB sound makes it go between 98,000 and 102,000. A 180 dB sound makes it go between 80,000 and 120,000.
So what happens when we hit 200 dB? It’d want to swing from -100,000 to +300,000 but air pressure can’t go negative you just hit 0 and have a vacuum. The end result is that above about 191 dB you just end up with a shockwave that has pressure climb wayyyy up then drop all the way to 0. Anything with more energy can only make the peak higher but the valley is bottomed out so it looks very different when measured
If you were somewhere like under water or in denser gas then you could maintain a much higher pressure differential and still have useful sound and not just a drop to 0 pressure.
A shockwave is a large pressure difference that propagates through a medium (air) caused by various phenomena such as explosions, or a sound source traveling at or faster than the speed of sound. As these waves pass over objects they can be very destructive as the pressure interacts with the objects.
Sound is a pressure wave and the volume of the sound is the difference in pressure over a wavelength. The question is how loud would the sound need to be to produce the same pressure difference as a shockwave. Pretty fracking loud.
So the reason a really loud sound is a shockwave is because sound is a pressure wave just like a shockwave, but the pressure difference in a normal decibel sounds are much (orders of magnitude) smaller then a shockwave. If you increase the volume the pressure difference of the sound becomes larger. Increase the volume of the sound enough and the pressure will become great enough to have shockwave qualities.
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