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?

Question

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?

In: 9

Answer 1

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.