Acoustics write up part 3 (the Mechanisms of Human Hearing)

7/23/2019 Acoustics write up part 3 (the Mechanisms of Human Hearing)

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Matthew Range

The Mechanisms of Human Hearing

The human ear is an important and complex part of the human body, it has many different attributes

within it which allows us to hear. We take advantage of the fact that we are able to hear as we do

this every day in a constant loop. The ear is split up into many different parts, which you will know

about at the end of this article. Without us humans having hearing we will not be able to do the

simple thing as communicate with our friends and family, we will also not be able to hear

soundwaves created from noises or instruments. This means that we wouldn’t be able to hear music

which then means the world would quite possible be boring.

The structure and function of parts of the ear

The ear is split up into three main parts with loads of parts of the ear within them. The three parts of

the ear are; the outer ear, the middle ear and the inner ear. Within each of these parts there are

many different mechanisms that all work together to allow us hear the simple sound, the ear is very

complex so having it split up into different parts will allow us to understand.

The outer ear:

The outer ear consists of two components that allow us to hear and work with other components.

The two components in the outer ear are the ear flap and the ear canal.

The first component of the outer ear is the only visual part that you

can see of the whole complex part of the ear. This part is the ear flap

known as the pinna, the main objective of this part of the ear is there

to provide protection to the middle ear. This is because if the middle

ear gets damaged it will affect the ear drum which is the most

important component of the ear, if the ear drum does get damaged it

will cause hearing loss which means you may be unable to hear. The

pinna is also there to direct the soundwaves towards the ear canal so

the other components in the middle ear and begin to work. By the

pinna doing this is will allow you to hear all soundwaves that pass you

as they are being directed into the middle ear.

The second part of the outer ear, which is the second part in the line

of which sound travels to the ear drum is the ear canal. The ear canal

is a 2cm tube which directs the soundwaves towards the ear drum.

Because of the length of the ear canal, it is capable of amplifyingsounds with frequencies of approximately 3000Hz. Sound only travels

through the ear canal, it’s basically acting as a pathway for

soundwaves to pass through to the next stage.

The middle ear:

The middle ear is more complex than the outer ear, as this is made up of another 2 components, but

these two components are important but within themselves they are also complex. This part of the

ear is air filled as all the air that has passed in has come from the outside which carries the air

particles which are soundwaves.

The first component of the middle ear is the ear drum. The ear drum is a tightly stretched membrane

that vibrates when incoming sound waves reach it. The compressed waves hit it which make the



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membrane vibrate. If the ear drum did not vibrate it will mean that you wouldn’t be able to hear as

it needs to vibrate to ensure that the next part of components in the middle can work. As the

vibration ensures the next part of the middle ear works.

The second component of the middle ear is split up into three different types. The middle ear is

essentially 3 different types of bones that move when the eardrum is stretched and expanded. The 3bones that will move from the pressure of the ear drums are; Stirrup, Hammer and Anvil. Together

these 3 bones are called the Ossicles.

The stirrup bone is the smallest bone in the human body, this bone is connected to the eardrum and

what this does, like the other bones, ensures the connection is complete and passes the vibrations

that are created on to the next stage.

The next bone in the link is the hammer bone, which carries the vibration to the third bone which is

the anvil.

The inner ear:

The inner ear is the most complex part of the human ear as this is where most of the hard and

confusing parts happen. The inner ear has 3 components within it, these components are; Cochlea,

Auditory nerve and Eustachian tube.

The first part of the inner ear is the cochlea, this carries on straight from the anvil bone which is still

carrying the vibrations from the eardrum. The cochlea is a snail shaped canal which is full of a liquid.

The cochlea is a sense organ which turns the sound waves into nerve impulses to be sent to thebrain. When it is sent to the brane it means that we are able to hear it, as the brane is the main

object that allows us to hear and feel things. The whole length of the cochlea can stretch up to 3cm

long if it was unravelled from its snail like shape. The cochlea also has 20,000 hair like nerve cells

which perform a vital role in allowing us to hear. Without the cochlea we would have nothing send

up to our brain which in total will allow us to hear.

The second part of the inner ear is the auditory nerve, this is important as this is a string of nerves

which link the brain and the cochlea together. Without this component all of the work that the

cochlea has done will not be able to be sent to the brain. Which in turn means that we will be unable

to hear.



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The final part of the inner ear and the whole complex components of the ear is the Eustachian tube,

this is here to simply reduce air pressure within your ear. This is very important as if you have high

air pressure within your ear it will be highly uncomfortable but also it will be difficult to hear. It will

feel like something is stuck at the bottom of your ear and will be very irritating. This tube is also to

drain infections and debris that may be deep in your ear, however this tube can have problems, one

problem that it can have is that it can get blocked so if you do get an infection it cannot be taken

out.

It’s crazy to think that all of these separate complex components work together very quickly

constantly throughout the day to allow us to hear. If one component fails it will be harder for us to

hear and will cause day to day life to be a struggle.

The limits of hearing

Within the world there may be limits in hearing, this could be the environment you are in or

depending on how good your hearing actually is.

The range of human hearing is 20Hz to 20 kHz this means that humans can only hear things that

create frequencies which are between these ranges. For example if a sound created a frequency

which is 25 kHz we would not be able to hear it as the frequency would be at a too high of a level.

However if a frequency of a sound is 19 kHz we will be able to hear it as it is in the frequency hearing

range. A good exercise to use within logic is the harmonics tutorial which has been explained further

up.

Another limit of hearing is how far a human can actually hear. This is all depending on how the loud

the sound is itself, for example if it was casual chatting a human can listen up to 20 metres away

from where the source of the sound is actually coming from. If it was shouting then a human can

hear it from 100 metres away. It’s good to know the certain range of human hearing itself as when

communicating with people they might not actually hear you depending on how far away they are

from you and how you are speaking to them.

Have you ever had pain while listening to music too loud or have a loud noise such as a police car

pass you in the street? This might be because that noise has reached the threshold of pain. The

threshold of pain is when the decibels (dB) of a sound is too high and it can damage you eardrum.

Sources say that the threshold of hearing is 120 dB, for a matter of fact this is also the decibel level

which is at the end of the frequency spectrum, so any sound which is higher than 20 kHz means it

will cause damage to your ear and will possible deafen you. In order to stay safe ensure that you are

aware of how loud you listen to music as if you are listen to anything that is near 120 dB you should

be wearing ear protection.

A way of calculating decibels is using the Bel scale, the scale shows how loud certain objects are and

how intensified they are if you was to hear them for a certain amount of time. The bel scales is



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measured by using a thing called bels and this is when for example the if the intensity level was 1000

it would be measured as 3 bels, or if the intensity level was 1,000,000 it will be measured as 6 bels.

In order to know how many bels an intensity is all you have to do is count how many zeros there are

and that is the number of bels.

Looking at the graph you can seethat a shotgun is the highest noise

on the decibel scale which means

without using ear protection this can

cause the most damage to the ear as

this is at 160 on the scale. On the

other hand a pin falling is on 15 on

the scale so you can imagine the

difference between the two as you

can hardly hear a pin drop in some

circumstances.

Psychoacoustics

Psychoacoustics is the scientific side of hearing and how our ear works, this uses tests to see how a

humans ears actually work. Psychoacoustics studies the psychological responses to sound, so this

how all of the mechanisms inside our ear actually work with our brain. For many people this can be

different to one another, such as people can hear better out of one ear better than the other for no

reason.

One way of explaining how the brain and ear works together is the cocktail party effect. The cocktail

party effect proves to show how we can focus on different things around us with the majority of the

time not realising that we do it, us as humans have the ability to

tune into other people’s convocations or other noises around us

without actually being there and properly focusing on it. Imagine

yourself at a party and you are standing with a group of 4 to 5

people however, there are other groups of people around the room

talking about something that is totally different to what you are

talking about. Without even realising it you can tune into another

convocation that is happening at the other side of the room and

listen to exactly what they are speaking about even though you are

not in the convocation and are even standing with them. The reason

for this is that your body is always aware of what is going on around

you, and if it hears any type of word that gains your brains interest it creates a stimuli to make your



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body alert and more focused, the reason for this is because your body doesn’t want anything bad

happening to it. In theory it is a safety mechanism.

The Haas effect is another example of psychoacoustics, this is when we are able to determine the

location of a sound around us. Although the pinna of our ear is facing forward and is there to direct

soundwaves into our ear, we can also hear sounds that are coming from behind us. This used to beextremely helpful when we used to be barbaric cavemen as other animals that wanted to kill us

would try to sneak up behind us. However because of this skill we was able to hear them and was

either able to kill them or try to escape. Without this we could have died from our prey and maybe

not exist today.

The masking effect is caused when a sound of one object is over shadowed and drowned out by

another noise from another object. For example if you are in the street talking to a friend you can

perfectly hear the convocation as the soundwaves from one another are able to reach your ears with

no problem. As you are having a nice chat suddenly a large loud truck drive past and then all of a

sudden you cannot hear the convocation you are having as the trucks soundwaves are larger and

more frequent when reaching your ear. This means that the soundwaves of the truck cover up thesoundwaves of the convocation which means you cannot hear it, or not able to hear it as clear as

before the truck appeared.

The Doppler Effect and beats are also good examples of psychoacoustic which has been explained

further up in the article.

Health and safety

In all aspects of anything you do in the world today health and safety is a highly important matter

which should be taken into an account at all times. Especially when it comes to your hearing as when

it is lost it is gone forever and there is no way of getting it back, if you lose your hearing that means

that your life becomes a whole lot harder.

To ensure safety at all times within workplaces there are now workplace laws that are enforced to

ensure that workplaces are safe to work in, this means that there has to be a limit on how loud a

work environment can be. The work environment limit at present day is now 85 decibels at all times,

this is for any working environment within the music industry. If an environment is at a higher level

then these and people get ear damage, fines can be issued. When a new worker is in training the

noise levels must not exceed 80 decibels as they are in training and are learning the environment

and are also a rookie which means they may forget to put their ear defenders on at one point and

could get ear damage from that one time. These set of rules are the ‘the control of noise at work

regulations 2005’.

There are simple pieces of safety equipment that will ensure that your ears and hearing are

protected at all times. The ear protection that you can use is ear defenders and ear plugs.



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Ear defenders:

Ear defenders are a larger more industrial way of protecting your ears as they

are for large work places such as constructional work. However ear defenders

can be used at things such as musical festivals if you are planning on being right

next to the speakers. Ear defender offer over ear protects and do not allowmany of the soundwaves to pass, however you can still hear things but only

slightly which means your ears will certainly not get damaged. Ear defenders

tend to be made out of hard plastics which mean that they are highly durable.

Ear plugs:

The really good earplugs fit fully in your ear, as they squeeze into your ear canal. Both

ear plugs and ear defenders do the exact same job and both do it highly similarly.

However because earplugs are smaller they are easier to carry around and use in

other places other than a construction site. An example of someone who uses ear

plugs is a DJ as they need to protect their ears too, because the ear plugs are so small

they are able to protect their ears without knowing they are there but also do things

such as using their headphones to mix with while their ears are 100% safe. Ear plugs

are genuinely made out of rubber or foam materials this ensures that they are

comfortable while offering the most protection possible.

Without ear protection we will have no way of protecting our ears when it comes to loud

environments, so if you are exposed to loud environments often such as work you will easily lose

your hearing in a matter of years. This is not good as it can cause pain and it will also make your life a

lot harder.

Within a studio environment it is highly recommended to not have the monitor speakers loud as

they are highly powerful little speakers, and because studios tend to be in small environments the

sound is always going to be within the small space. While more soundwaves are being create the

other ones are still bouncing off of the wall and travelling around the room. So it is wise to not have

it loud as the continuous production of waves will be too loud while the other ones are still travelling

around the room.

It is highly important to be aware of the volume of everything or what kind of pieces of equipment

you are around, if you know it is going to be loud wear ear protection otherwise you will regret it

and either be in pain or have no hearing at all.

Documents

Acoustics write up part 3 (the Mechanisms of Human Hearing)