If sound goes through solids more easily than air, how do foam and silicone earplugs sound instead of amplifying it when it hits your ears?
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Sounds *generated* in solids travel faster and further. However, when sound has to transition between materials, it loses a lot of energy. This is why sound generated underwater can travel a really far distance, but people underwater can hardly hear anyone shouting at them from outside the water.
Because they’re soft and squishy. Sound is a compression wave. Because the molecules of a solid are so much closer together than the molecules of a gas they “bump” into each other sooner and so the sound is transmitted faster.
Foam or silicone earplugs are squishy so a greater portion of the energy of the compression wave is absorbed by the material itself rather than being transmitted.
Imagine you want to push a box and you have to do it with something. If you push using a thick branch, a stiff and relatively incompressable object, most of the energy you impart on the stick is transmitted to the box. But if you use a thin and whippy twig most of the energy will go into bending the twig and very little will be left over to push the box.
foam earplugs are like a twig, the sound spends most of it’s energy moving the earplug so whatever is left over is greatly reduced by the time it tries to push your eardrum.
Plus sealing off your ear canal makes it so the sound waves *have* to go through the plug and some of the energy will go back into the air, effectively bouncing off, instead of being transmitted to the far side of the earplug.
**Edit**. See the response below mine.
“More easily” isn’t really the best way of thinking about it.
The more dense the material, the faster the speed of sound (or a pressure wave) travels though it, but the more energy it takes to create that wave.
You don’t get anything for free, the sound wave speeds up, but its power is then reduced. So when the sound wave comes out the other end of the denser material, it’s slower again, but also at much lower power.
Transitioning between materials takes a lot of the energy out of the equation, which results in lower volume.
We hear sounds based on little bones in our ears. When sound waves travel through the air our ears catch the waves and bounce them into our ear canal which amplifies the sound. Vibrating the little bones that our brains register as noise.
When you put a seal over our ear canal it stops the amplification of sound waves that are traveling in the air. So high energy sound waves say coming from a loud machine get dissipated as heat inside the ear plugs.
Having a improper seal from ear plugs can result in sound waves still coming in and damaging your ear drum which is just a thin membrane that vibrates with the bones in your ear.
They do amplify your internal sounds a lot more than external sounds. You’ll hear your own body making sounds like your breathing when you wear earplugs because it’s creating a resonating chamber inside our ears. So lower frequency sounds that our bodies make will be amplified but high frequency sounds that come from external sources are muffled because our ears are blocked from letting sound travel into our ears to get louder.
It’s actually impossible for us to make a sound proof earplugs. We can get close with electronic ones that try and cancel out frequencies of sound waves by reproducing them. But you’ll still hear sounds through the vibrations of our skulls.
Hope this was simple enough, if not I can try to TLDR it more.
Mass blocks sound. Incoming sound wave has x amount of energy. It is enough to move a cubic centimeter of air which weighs almost nothing. However, the sound wave does not have enough energy to move a cubic centimeter of foam (much heavier) to the same degree. Sound needs energy (loudness) to move mass to travel through it. If the mass is too much for a given loudness, the sound can’t move the mass and the sound doesn’t travel in it. Even if the actual travel speed would be higher if it DID have enough energy to move the mass.
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