There are several ways to keep sound out if you're soundproofing your home recording studio.
There's a whole world of sound, called infrasound, that your ears can't pick up. Learn more, on this Moment of Science.
Unlike waves on a lake, sound waves don’t travel up and down. Instead they’re more like layers of high and low pressure traveling outward in all directions. Each wave consists of a layer of high pressure followed by a layer of low pressure.
When the bottle vibrates, the water inside has to vibrate with it. Having to move all that water slows down the vibrations of the glass and that in turn slows down the frequency of the sound waves, producing a lower pitch. Adding more water slows down the bottle’s vibrations even more, creating an even lower pitch.
Have you ever noticed that when you hear your own voice on tape it doesn't sound like you?
By temporarily altering the shape of the pinnas with plastic molds, researchers in the Netherlands found that indeed, people with new pinnas had a hard time locating sound sources.