How Does Soundproofing Work?

Charles from Altoona, PA, has an older brother that plays the trumpet. His brother practices the trumpet in the bedroom next to his. He wrote in asking if it was possible to block out the sound so that he does hear the trumpet while he’s in his bedroom. Charles is essentially asking about soundproofing. While he probably won’t be able to block all the sound from his room, Charles can take steps to minimize the sound that he does hear.

Average volumes of people talking, television sounds, and music playing can often be heard through walls easily. This is due to the fact that sound is a series of vibrations that move surrounding particles. The series of vibrations, or sound waves, carries the noise from the noise source across the room to our ears. Since particles are required to carry the vibrations, sound cannot travel in a vacuum. The more densely packed those particles are, the better the sound moves through since the particles don’t have to move the surrounding particles much. When you’re in an open field, though, you would notice that sound will not carry as well since the particles are more spread out. The farther sound waves have to travel from one point to another, the fainter the sound will become. When sound waves collide with a solid surface (e.g., a bedroom wall), there are a few things that can happen. The surface will reflect some of those vibrations back toward the source, it will absorb some of the sound by converting the vibrations into heat energy or it will transmit the vibrations to the other side (i.e., into the bedroom).

There are two main things to consider when soundproofing: noise transmission and noise reception. The sound coming from the trumpet is a noise transmission issue, while the desire to block the sound out is a noise reception issue. Next the source of the noise should be considered: the indoor noise vibrations your body feels are structure-borne noise, while overhearing a conversation is airborne noise. Soundproofing can be achieved by considering space, mass, and dampening. Space increases the amount of air between your ears and the source, which diffuses the noise by taking away the vibration channels. Mass, like a bedroom wall, can act as a sound sponge that soaks in the sound waves. Dampening sound requires specific materials (like insulation) that will convert structure-borne sound waves to heat energy. Dampening can be expensive.

Without having to spend money, one step Charles can take while his brother is practicing the trumpet is to create more distance between himself and his brother. For example, Charles can plan to hang out in the basement or another room in the house that’s far away from his bedroom while his brother is practicing. Or Charles could ask his brother to practice in another room that’s far away from his bedroom.

Little Lion Experiment
You cannot see sound waves in the air, but you can see their effects. This experiment will help you see the effects of sound waves. You will need: 1 large cake or cookie tin, 1 sheet of plastic wrap, 1 long rubber band, 1 baking tray, 1 wooden spoon, and some fine sand.
Steps: 1) Make a drum by stretching a piece of plastic film over a large round tin; 2) Stretch the rubber band around the tin to hold the plastic taut; 3) Sprinkle a teaspoon of sand on to the top of the plastic drumskin; and 4) Hold a baking tray above your drum, and hit it sharply with a wooden spoon.

What did you observe? What do you think caused the sand to dance up and down on the drumskin? When you struck the baking tray, the metal continued to vibrate for a fraction of a second afterward. As it vibrated, the air around is also vibrated. These little vibrations in the air, the sound waves, quickly work their way out through the air in all directions. When the sound waves hit the drumskin, the drumskin is vibrated too, which causes the sand to dance up and down on the drumskin. The sound waves that reach your ear make you hear the bang.

How Do Sounds Travel In Space?

Everyone loves movies, they can make us laugh or cry or jump out of our seat! But when it comes to science, movies do not always tell the whole story.

Movies set in space are a great example. Have you ever watched a movie that is set in outer space and heard an explosion? This would never happen in space. As most of us know, space is a vacuum; this means there is a whole bunch of nothing in the air. The air here is made of tiny molecules like oxygen, nitrogen and carbon dioxide. In space, these molecules are few and far between. Sound is a wave, like in the ocean and needs molecules to be carried. So just like ocean waves need molecules of water, sound waves need molecules of air to move and be heard.

We are able to see in space because light travels in a different kind of wave called an electromagnetic wave. Electromagnetic waves do not need molecules to send their wave. Another thing related to light and sound is that they do not travel at the same speed. Sound travels at 760 miles per an hour here on earth. I would like to see Jeff Gordon beat that! In space because there are so many less molecules, it would be much slower. We are not talking slow like a turtle, but slow like going only a foot or two over millions of years. Light travels at 671,080,887 miles per an hour in a vacuum like space. We would see the explosion long before we would hear it. This is the same thing that allows us to see lightning before we hear it.

And just another point about space settings is the ever-present exploding planet or spaceship. Pieces of the planet or spaceship created from exploding objects would have an extremely high initial speed, like on earth, and then continue forever in a strait path through space. Here on earth we have gravity to slow exploding objects, in space there is little or no gravity, so the debris would travel outward in straight lines ideally forever until it impacts with something. These exploding pieces would have about the same energy or force they had at the moment of explosion, so if they impacted a ship or planet, no shield would be able to protect you!

Little Lion Experiment:

Explore physics for yourself! A common physics topic is pressure. Pressure is just the amount of force distributed over the amount of area that force is given. For instance, if you took your finger and pressed it into the arm of your sibling or parent, it would hurt quite a bit. If you used the same amount of strength and pressed into their arm with your entire hand, it would not hurt much at all. Lets try the same thing a different way!

Materials

• Paper Cups
• Big thin book or piece of flat, thin plywood

Steps:

1. Step down on a single cup. What happens?
2. Take the paper cups and lay them in a square a little bigger than the size of the book or plywood. Fill in the square with cups so that the cups are all right next to each other.
3. Place the book or wood on top of the cups.
4. Have your parents help you as you step on top of the book or wood. What happens? Do the cups break as they did when you stepped on just the one?

So what happened is the force (your weight) is distributed over all the cups instead of just one cup. So the cups are able to hold you up! This is the same way a bed of nails works. If you lay on one nail, OUCH! But because your weight is distributed over several nails, it is just a little prickly.