Amplifying the Sounds That We Hear: How Does It Work?

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Published: 08th August 2012
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Most of the time, the changes in air pressure are relatively small. They do not apply a lot of force to your eardrum, but since it is extremely sensitive that minuscule amount of force will cause it to move at an increased distance. The cochlea within the inner ear works like a conductor to send the sound through the fluid, instead of sending it through the air. This specific fluid has a larger amount of inertia than that in air, which makes it a lot harder to move.

If you think of it in terms of how difficult it is to push through water versus being able to push through air, it will make much more sense. Since the amount of force that is felt at the drum is so small, it is not able to move the fluid. Before any noise is passed onto the inside of the ear, the amount of pressure within the ear is going to need to be amplified.

The whole process is the responsibility of the ossicles, which are a small grouping of bones within the middle ear. They are essentially the tiniest bones found within the human body. Ossicles are composed of:

Malleus - Hammer
Incus - Anvil
Stapes - Stirrup

The malleus is attached to the middle of your eardrum, which is on the inside. Once the drum vibrates, it will move the malleus to and fro, similar to that of a lever. On the opposite end of the malleus is the incus, which in turn is connected into the stapes. At the opposite end of the stapes is the faceplate that rests up to the cochlea alongside an oval window.

Whenever there is air pressure that pushes into the eardrum, the resulting ossicles will end up moving the faceplate, which pushes the stapes into the fluid within the cochlea. As the air pressure from the rarefaction pulls the eardrum out, the ossicles will move in a manner that pulls the stapes into the cochlea fluid. As a result, the stapes are similar to that of a piston. They work to create waves within the fluid of the inner ear that help to represent the varying fluctuations within the air pressure of the sound waves.

The ossicles work to amplify the forces from within the eardrum in one of two different ways. Mainly the amplification comes from the varying difference between the stirrup and the eardrum.

Eardrums have a surface area of roughly 55 millimeters square, whereas, the stapes only have an area of around 3.2 millimeters square. Sound waves work by applying force to every single inch of your eardrum, with the eardrum working to transfer all of the available energy into the stapes. If you take this amount of energy and concentrate it into a smaller space, the pressure is going to become a lot more intense.

The way in which the ossicles are configured controls how the sounds are amplified. Mallei are longer than the incus, which works to form a lever between the stapes and the eardrum. Even though the incus moves with an increased amount of force, the malleus moves at a far greater distance.

This whole process for amplifying sounds is extremely effective. The amount of pressure that is applied to the fluid within the cochlea is roughly 22 times as intense as the amount of pressure felt within the eardrum. It is enough pressure to pass the required level of sound into the inner ear, which is where it is then translated into something that the brain is able to understand thanks to the nerve impulses.

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