How Sound Works - The Miracle of Sound

How does sound work? It truly is a miracle that we can perceive sound. Have you ever thought about the number of events that must take place before you hear a sound? For us to be able to perceive sound, a complex set of these events must take place in a very specific order. If one of these events doesn't occur, or changes the way it handles its task, we may not even hear a single whisper.

Take a short journey with me and we'll explore the complexities of these events that we'll now collectively call the Miracle of Sound. This is how we are able to hear.

A sidebar before we start

What we perceive as Sound is the result of air molecules bumping one against the next from the source to our ear (and eventually processed as electrical signals that our brain can understand). We call this 'Vibration'. As the molecules are disturbed at the source, they vibrate. As they vibrate, they bump against the closest molecule which also begins to vibrate. In this way, sound reaches our ears from the source.

The Sound Source

Consider that I'm sitting at a Piano and I press on the key 'C'. As I press the key, a hammer (covered in felt) is moved upwards at the same pressure. It's a levering action. This hammer strikes a string and the string will begin to vibrate.

It's true, a Piano is a String instrument :)

At the other end of the piano, the string is connected to a Bridge. The Bridge passes along these vibrations to the Soundboard and the Soundboard now begins to vibrate.

The Sound Conduit

The Sound Conduit is the air around us. As the Soundboard vibrates, the air molecules around the Soundboard are set in motion. These molecules bump one against the next resulting in the transmission of energy (the sound energy). The sound energy has now left the source! It works it's way to our ear using this bump action which resembles Newton's Cradle.

Sound Energy is really Kinetic Energy that is passed from one molecule to the next (when the molecules bump)

For the image below, assume that each ball is an air molecule. There are hundreds of thousands of air molecules between your ear and the sound source (the piano). The air molecules bump one another and spread all around the room.

Sound Cradle

This bumping action is called a wave and it's sort of like what happens when you drop a stone into a calm lake. The stone would cause energy to be passed along from molecule to molecule and we'd see that as the effect of a wave pouring out from where the stone landed in the water. We'd see it as a small wave. The difference with sound however is that this bumping action is not only seen as a 2 dimensional effect. It's more of a 3 dimensional effect where the sound waves pour out in all directions at once.

How we find the Source of Sound

Some of these molecules, as they're being bumped by the previous one, reach your ear directly. Some of them bounce around the room and reach your ear a little later (a fraction of a second later). If the piano was sitting a little to the right of you, and you weren't looking at it directly, more air molecules would reach your ear directly from the right. Most of the sound you'd hear in your left ear would be the result of these molecules passing the energy one to the next all around the room where it finally reaches your ear. When this energy reaches your left ear a little slower, our brain perceives this difference in time as 'Direction'. It's what helps us understand where in the room the sound is originating from.

What is amazing is that when sound reaches one of our ears a fraction of a second slower than the other, we are able to notice the difference and we can turn our heads quite accurately so that we reduce this delay effect until it sounds like the molecules are arriving evenly. This is our locating mechanism. We use this to figure out where the source of the sound is originating.

The Sound Processing System

As the air molecules transmit this energy which finally reaches your ear, your Ear Drum (which is a very thin membrane) begins to vibrate. The Ear Drum in turn makes the 3 middle-ear bones (Hammer, Anvil and Stirrup Bone) vibrate. These 3 bones then make the fluid in our inner ears to move back and forth which then makes the Basilar membrane (in our inner ear) vibrate.

These vibrations are eventually converted into electrical impulses that our brain perceives as sound.

The amount of information that is contained in these vibrations (waves) can numb an engineers mind. It allows our brain to perceive:

  • What type of instrument was played (Timbre)
  • How long the pitch was played for (Duration)
  • What part of the room the sound came from (Origin)
  • How loud it was played (Amplitude)
  • etc.

The Miracle of Sound

Imagine all this information is transmitted by just bumping air molecules one against the next. What if just one of these events, instruments or processing systems failed, or was to be just a bit out of sync, or maybe partially damaged? The sound would either be coloured so heavily that we wouldn't be able to understand it, or we wouldn't hear the sound at all!

Imagine also that these actions happen at a very fast rate. We hear almost instantly - sound travels at 340m/s. This means if a Piano was about 5 meters away from you, the sound would get to your ear, be processed and understood by your brain, in about 0.02 seconds. That's fast.

What if we played more than one sound? Imagine the complexity of having numerous sound sources such as a Piano, a Violin, a Bass all playing at the same time! The gazillions of molecules working to move the vibrations all around the room is unimaginable.

It's really a miracle how we hear sound. It's a miracle that we have the exact tools we need to accurately reproduce the vibrations around us.