How Do We Hear Sound?


In order to understand the music and sounds that we are listening to, we must first understand how us, as humans process the pressure waves in the air that are referred to as ‘sound’. In order to do this, we must explore the inner-workings of the human ear.


A diagram of the human Ear



When a sound is produced, a pressure wave is sent through the air and into the human ear where it is transformed into a mechanical wave so that the structure of the ear can ‘hear’ it.

The human ear can be divided into three different parts which are highlighted in the picture above. These three parts of the ear help us to process the sound, what it means and where the sound is coming from in space.The main purpose of the outer ear is to take in as much sound as possible and channel it into the auditory canal and into the middle ear where the sound can be processed.  The size of the ear helps to take in more sound and the shape helps to bounce these sound waves into the middle ear. The auditory canal is approximately two centimeters long; this length helps to amplify the more quiet sounds so that they can be more easily processed by the middle ear.

The middle part of the ear is made up of three bones and a tiny membrane that transfers the pressure waves into mechanical waves.  When sound hits the flexible membrane, it vibrates the membrane back and forth at the same frequency that was traveling in the air. This is demonstrated in the diagram below.  Since the eardrum is connected to the stirrup, hammer and anvil, all three of these bones will vibrate at the same frequency as the sound that is entering the ear. This wave is again transferred to the inner ear to create compression waves in the inner ear fluid

A diagram of the eardrum transferring pressure waves into mechanical waves

In the inner ear, the waves are transferred into an organ called the Cochlea which is filled with a water like substance. This organ is approximately three centimeters long and is filled with thousands of tiny nerve cells that are designed to vibrate naturally at a certain resonance. When a single nerve is struck by a frequency like this, it will vibrate at a higher amplitude that this will be picked up by the auditory nerve and sent to the brain


The Cochlea