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
In: 18
I believe the bubbles create multiple air water air water transition steps.
Imagine being under water in a pool.
If some on the deck were to shoot a gun you would probably hear it. If you were to shoot a gun or scream loudly the person deck might not hear it well.
Foams block sound because of the way liquid is distributed throughout them – the large but thin film of the bubbles and the narrower but more voluminous channels that support the bubbles. Sound is just the vibration of molecules, and it turns out that at the frequencies we tend to hear best at, the sound transferring from the air causes the bubbles to vibrate in the *opposite* way it affects the channels, meaning they cancel each other out. Thus we don’t hear anything.
[Source for those interested.](https://www.sciencedaily.com/releases/2014/04/140424102254.htm)
it’s like this….
you have a brick resting on your hand. you slap the brick, it hurts your hand, right?
now, you ahve a bag of beans, or rice, or whatever that is small but fills a bag. You slap the bag, you feel the impact but it doesn’t really hurt.
now, you have a balloon, or an inflated bag/pillow/sack of some sort, resting on your hand. you slap it, and you still feel the impact, but not to the same degree and doesn’t hurt at all.
what you just did was demostrating the properties to transmit energy of the thre matter states. Solid, liquid(particle in this demo), and air (plasma excluded). you can observe that the solid transmits it the best, and the air the least.
Sound is a form of energy, energy is transmitted through air the least efficient (balloon scenario).
So, having bubbles in your ears is placing an air barrier in your ears. You should also experiance the same with putting [sound proof headphones](https://www.amazon.com/Soundproof-Protection-Headphones-Adjustable-Prevention/dp/B07PZKM13L) on your head, which creates an air pocket/barrier over yoru ears. it should perform similiar to bubbles.
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.
Insulation is just a series of “bubbles” to block heat, or noise.
The best types of insulation have cavities small enough so they don´t actually have air in them.
Soundwaves also need parallel surfaces distanced on the right frequencies to travel through effectively. A series of random sized bubbles with curved walls will break apart sound waves and distribute sound, mufflling it.
Sound transmits poorly through varying materials, especially when air gaps are introduced.
For soundproof walls, air gaps effectively “decouple” the main wall assembly components from each other, reducing the ability of low-frequency sounds to easily transmit through the full assembly.
Every time sound changes what substance it’s passing through, some of it is lost and some of it turns backwards.
For instance think of sound echoing off walls in a cave – some of the sound has gone into the wall, but a lot has come right back at the source.
In a foam a straight line goes “soap, air, soap, air, soap, air, soap, air, soap, air, soap, air, soap, air, soap, air” and at every comma in that list some of the sound is being lost.
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