I have noticed this while bathing when soap foam went into my ears and it almost completely blocked the outside sound. This seems weird as soap foam is just all air with some liquid
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Air is light and springy, liquids and solids are very heavy and stiff compared to air.
When sound (which is just the pressure of air going up/down) hits a solid/liquid surface, it pushes on it, which causes the surface to move slightly. Imagine a wall, the sound causes the wall to vibrate slightly. However:
1. The wall doesn’t move very far because its heavy and stiff. If the alternating air pressure is changing whether its pushing or pulling on the wall every 0.001s the wall simply can’t move far in that time. This means very little sound energy is imparted to the wall, since the energy can’t just dissapear, most of it is reflected.
2. Of the small fraction of sound energy that does cause the wall to move, that does propagate extremely well through. However, since the wall isn’t moving very much, on the other side of the wall, it doesn’t cause the air to move very much, so the sound level is much lower on the opposite side of the wall.
Bubbles create hundreds of liquid/air interfaces, each one attenuating the sound. The foam’s liquid component is about 700 times denser than air, so even though the bubble’s film is thin, it still attenuates.
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