QUESTION: What little symphony did you hear this morning? What combination of competing or syncing conductors and their twirling sonatas of chance found their way inside you ears? Or, is it such a familiar song that you ignored it entirely?
Every sound we hear follows the same general process. It’s all just air doing nothing. Things happen, and suddenly nothing becomes something. The nothing encounters an oscillator. An oscillator is…well…anything that causes changes in air pressure to take on a wave shape1. This could be you, a dog barking, people having sex. These sudden wave shapes can take different forms; big or small, loose or tight. This. This is sound.
Let me tell you something: every sound we perceive is a wave.
Sound waves do not have peaks or crests like an ocean’s waves. They have compressions and rarefactions. You should consider a sound wave to be a pressure wave, just like an electromagnetic wave. The frequency of a sound wave is determined by counting the wave’s movement from compression, to rarefaction, back to compression. Each time the wave rarefies and begins to “slow down” it is propelled by the compression behind it, causing it to compress again and push forward a little more, until it rarefies again. At that point if the air behind it is still compressed enough, the cycle repeats and the wave continues moving forward. We can measure the intensity of these waves with an oscilloscope2. The higher the amplitude at it’s source, the “farther” it will travel before fading away.
How then is the wave able to continue compressing and releasing? Resonance. Picture this; someone has shot a green laser pen directly across your field of vision. What do you see? A line mostly. But this line is being projected out of the pen from left to right. This line is horizontal. While this green laser is moving (to the best of your cognizance) completely horizontally, the waves we use to measure its frequency are actually moving vertically, up and down. They are moving AWAY from the source of the wave. These transverse waves3 can continue like this without any medium to travel on, through empty space. That is how we are able to see the light from the sun and other stars.
Think of it this way: how does a slinky slink? Applying pressure to one side of a slinky compresses coils of metal. They want to release, so they push away from the point of pressure into other coils which also want to be released. Repeat this exercise ad libitum and you have got a sound wave. Sound moves parallel to the initial impulse. When you strum a string on a guitar, the sound it emanates is loudest directly in front of the guitar. This is because the sound waves are traveling away from the string in a parallel path. You would hear the same sound sitting in line with the body or the head of the guitar as well, but it wouldn’t be as clear or as loud as it is when you sit in front of it.
Or…how about this: what happens if you have a plastic bag with air trapped inside, and you squeeze it? The air escapes from the area in the clutch of your hand, and moves to another part of the bag. Only now the air has less space to occupy. The molecules cannot move as freely as before. They have become compressed. You have formed the beginning of a sound wave, but managed to keep it in a vacuum. You are holding sound in the palm of your hand.
Go ahead and squeeze that bag tighter, and tighter still. Eventually it ruptures. Rarefaction. The air inside the bag, once tightly compressed into a small space is now released into a big open nothing. You know the bag has failed. You know because you saw it split. Even with eyes closed you know it burst because you heard it burst. The air was not yet rarefied to a relaxed state. It was still compressed enough that it had a force propelling it through the air and into your ears.
What caused the sound you heard? What made the bag sound like a pop instead of a shriek, or a heavy electronic bass drop? Frequency. You have managed to push your plastic bag past its breaking point of structural integrity and it tore. Did it tear over and over? Did it resonate? No, a thin piece of plastic tore once and released highly compressed air. A pop is the natural and expected sound for this occasion.
When a wave shape disturbs an air molecule it is pushed in a direction and fashion identical to the wave that pushed it, but reduced. The opportunity to hear the sound is increased if you are in a room though. The reason your Bluetooth speaker sounds better in your bedroom than it does at the beach is because of reverberation4. A sound wave is like a rubber bouncy ball. A rubber bouncy ball has a set density that, when compressed, will do it’s best to expand again. When you throw your bouncy ball at a wall it compresses against it and expands the only way it can—away from the wall.
Sound waves do the same thing. They move along their path, compressing and rarefying, until they hit a wall. At that point they do the only thing they can, compress against the wall until the compression becomes too great. Then they rarefy away from the wall bouncing off of it in the opposite direction. If you are listening to music in an enclosed room that means you will get the chance to hear your sound wave again, repeated in a quick enough succession to make the sound appear doubled, or stronger. If you are listening to your sound in an open field the wave will float away forever until it disperses.
When sound waves eventually do make their way to us, we sometimes have no control. We now know there is no difference between a harp playing and a sewer lid clattering, only the harp is designed to be pleasant to listen to. Maybe you find it pleasant, or maybe you hate it. That does not change the mechanical formation and molecular makeup of the waves they create.
Listen to the waves all around you, the man hammering a nail into a wall. The heels of the shoes of the woman who just walked past you. The leaves rattling against the ground as the wind pushes them. The bottles clinking against the tin table as a group of laughing friends put their drinks down. The rhythmic timing of these sounds, and the intention, is all that separates these sound waves from the sound waves in our “music”.
Maybe the rhythmic timing is not as different as we think though. Maybe we have dismissed these sounds because we were taught that music is music and sounds are sounds.
Maybe if we try hard enough we could find all the music happening around us.