Acoustics and Hearing Loss

Ciaron Murphy

Contents

Project Plan.................................................................................................................................................3

Aims.............................................................................................................................................................5

Rationale.....................................................................................................................................................6

Introduction.................................................................................................................................................7

Methodology...............................................................................................................................................8

Background info........................................................................................................................................11

The Physics of Sound.............................................................................................................................11

The Human Ear......................................................................................................................................14

Research....................................................................................................................................................19

Results.......................................................................................................................................................20

Conclusions................................................................................................................................................28

Evaluation..................................................................................................................................................29

Glossary of Terms......................................................................................................................................30

Bibliography and references......................................................................................................................32

Ciaron Murphy Page 2

Project Plan

September

Decided upon relevant field for project and discussed ideas – 12 /9/11

Conception of project title– 19/9/11

Began background reading related to project theme (hearing loss) - 26/9/11

October

Planned project in terms of structure and relevant information– 3/10/11

Considered method of primary research and desired results – 10/10/11

Researched into basic acoustics – 24/10/11

November

Began to consider appropriate questions to ask for questionnaire – 1/11/11

Researched into hearing loss and the causes of hearing loss – 7/11/11

Drafted introduction for project – 21/11/11

December

Wrote up questionnaire – 5/12/11

Planned how to display evaluated results – 12/12/11

Made predictions of expected outcome – 19/12/11

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January

Handed out questionnaires – 2/1/12

Wrote up introduction for project – 7/1/12

Received information back form questionnaires – 21/1/12

February

Began to draft introduction to acoustics– 5/2/12

Evaluated information from questionnaires – 12/2/12

Made charts/tables to graphically represent information – 26/2/12

March

Drafted section about hearing loss – 5/3/12

Wrote up introduction to acoustics – 12/3/12

Write up section about hearing loss – 19/3/12

Project deadline – 30/3/12

April

Learned how to conduct presentation – 14/4/12

Started to plan how to layout presentation – 21/4/12

May

First draft of presentation – 5/5/12

Final write up of presentation – 12/5/12

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Acoustics and Hearing Loss

Aims

The aim of this project is to research into people’s perception of how hearing loss occurs due to

acoustic trauma (exposure to noises which cause hearing loss). Whilst there are many causes of

hearing loss such as Ménière's disease, age related hearing loss and multiple sclerosis I will be

focusing mainly on hearing loss related to acoustic trauma. Noise induced hearing loss due to

acoustic trauma is easily prevented in a large majority of cases. The National Institute on

Deafness and Other Communication Disorders states that “the number of Americans with some

form of hearing disorder, over age 3, has doubled since 1971”

(http://uk.askmen.com/sports/health_400/466_noise-induced-hearing-loss.html#ixzz1qLkZ8aH6

– 12/1/12). This can be attributed to a number of different sources of exposure; however one of

the main sources is supposedly due to devices such as MP3 players.

My hypothesis that people’s perception of how and why hearing loss occurs is limited and

possibly some of the concepts are misunderstood. I also believe that there is an element of

misunderstanding or lack of information in terms of the publics’ perception of acoustic trauma. I

would speculate that people do not understand the levels (in terms of decibels) at which hearing

loss can occur and what kinds of sources of noise can be the most damaging.

Since one of the main sources of hearing loss related to acoustic trauma is supposedly due to

devices such as MP3 players, I also wanted to research into what people understand about the

difference between in-ear headphones and external headphones. I believe the public does not

fully understand that at the same volume levels, in-ear headphones are much more damaging

than their external counterparts

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Rationale

I am interested in hearing loss because I am an active musician, and my hearing is very important

to me. I would like to protect my hearing and other peoples hearing, so maybe one day they can

listen to my music. I am also interested in hearing loss because I am going to be progressing onto

a degree in acoustics. Acoustics, being the science of sound, lends a lot to hearing loss and its

prevention.

I feel that since hearing loss is increasing over recent years, it should be an area that is more

important in society and addressed accordingly. Information supplied by the National Institute on

Deafness and Other Communication Disorders states that ‘the number of Americans with some

form of hearing disorder, over age 3, has doubled since 1971’

(http://uk.askmen.com/sports/health_400/466_noise-induced-hearing-loss.html#ixzz1qLkZ8aH6

– 1/2/12). Hearing is such an important sense that when lost, can cause huge problems for the

person to overcome. We rely on our hearing for information about the world around us a lot

more than we actually perceive. Therefore I feel it is in the best interest of the public to have an

increased awareness with regards to hearing loss and its causes.

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Introduction

Hearing is a sense which is important to anyone who has it, and it is also a sense which is very

much taken for granted. Hearing can tell us a lot about our environment. Our ears are so evolved

that we can gain spatial information (for example about a room) or information about the

location and distance of a sound source. Hearing loss is becoming a more prevalent problem

within society due to misinformation about how hearing damage can occur, and ignorance to the

signs of it. I will be investigating the mechanics of the human ear since it is relevant to

understanding how hearing loss can occur.

Anyone who has been to a concert and stood too close to the speakers knows how loud noise can

damage their hearing, but they probably do not know the extent to which this occurs. Whilst

there are a number of causes that can be attributed to hearing loss, one of the most common is

too much exposure to loud noises. This can damage hearing permanently within five minutes, but

it can also have a cumulative effect, causing hearing loss over a number of years. Since hearing

loss occurs due to sound waves (as does all hearing), I will be researching how sound waves are

formed and their basic properties to further understand how they interact with the human ear and

why loud noises can cause hearing loss.

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Methodology

For my primary research I feel I must gauge the publics’ perception of how hearing loss can

occur, as there are a few sources which are prevalent in most people’s daily lives which they may

not even consider as being damaging to their hearing. To this end I will be conducting a

questionnaire which will try to achieve the goal outlined above to gain qualitative research on the

subject.

My questions will be mainly related to what sort of noise levels cause hearing damage,

perception of what kinds of noise will cause hearing damage the quickest, how different methods

of listening to music can causes more or less hearing damage than others. The rationale behind

the format of my questionnaire is that there are only a few ways in which hearing loss can occur

in most people’s daily lives, so focusing in on these was the course I decided to take. Although

that was my main focus I still needed to test what people knew about levels of sound in terms of

decibels since this is one of the things that most people will not have a lot of knowledge about.

A copy of my questionnaire is pictured on the following page.

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Hearing Loss Questionnaire

1. At roughly what decibel level does damage to human hearing start to occur?a. 0 dBb. 80 dBc. 30 dBd. Don’t know

2. What is the main cause of hearing loss?a. Loud noiseb. Ear infectionc. Poking things into your eard. Don’t know

3. When listening to music through earphones, what volume level would you have the music at?

a. Low levelb. Medium levelc. As Loud as possibled. Don’t know

4. Which of these scenarios is likely to damage your hearing the quickest?a. Normal conversation b. Using a power drillc. Standing near to the speakers at a concertd. Standing near a Bulldozer which is idling (not in the process of actually

Bulldozing)?

5. How long does it take for hearing damage to begin if you are listening to music through headphones at a high level (around 100 dB)?

a. 4 daysb. 8 hoursc. 15 minutesd. Don’t know

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6. How do you most often listen to music?a. Speakersb. In ear headphonesc. External headphonesd. Don’t know

7. If you were to listen to a sound at the same level using the above methods which could most easily damage your hearing

a. Speakersb. In ear headphonesc. External headphonesd. Don’t know

8. Other than hearing loss, what is another big health concern of loud noise exposure?a.  Hypertensionb. Diabetesc. Tinnitusd. Don’t know

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Background info

The Physics of SoundSound waves are produced by the vibrations which cause changes in air pressure; these can be

produced by a number of sources, such as your vocal chords, a guitar, an explosion or a

synthesizer. No matter what the sound source is, it is always produced by vibrations or changes

in pressure, which in air produce longitudinal waves. A longitudinal wave is a wave which

travels in the same direction as the direction of the vibrations causing them.

Fig 1.0

The changes of pressure which cause a sound wave to be produced and also allow sound waves

to propagate and travel through a medium such as air can be explained as a series of

compressions and rarefactions. This effect can be replicated using a slinky spring and is a

commonly used example. If you were to hold one end of a slinky spring in place, and then you

were to push the spring causing it to compact at the point closest to the point where you applied

the force, you would see this energy travel along the spring in such a way that there would be

areas where the spring was more compacted than it was originally and areas where the spring

would be more stretched out than it was originally. Such an example of compression and

rarefaction is shown in fig 1.0.

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The louder the sound wave appears to be corresponds to the difference in areas of high and low

pressure, this is why the volume of a sound can often be measured in terms of sound pressure

level (SPL).

It is possible to see certain objects producing sound waves, as they are vibrating slowly enough

for the human eye to detect the motion. A good example of this is a speaker producing a

frequency which is at the low end of the human hearing range (around 30Hz for example).

The speaker can be seen to physically vibrate and the sound produced can be detected by the ear.

However, the lower or higher we go on the spectrum of frequencies of sound waves, the harder it

is for the human body to detect, this is because our ears are calibrated to pick up a certain range

of frequencies. If you were looking at the speaker in the above diagram (presuming it is

producing a frequency at the lower end of the hearing range of an average person) you would see

the speaker cone vibrate, this vibration corresponds to frequency of the sound wave produced.

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Humans can generally hear frequencies in the range of 20Hz to 20kHz, whilst this seems like

quite a large frequency band (roughly 18980 Hz between the lowest and highest frequency the

ear can detect) there are huge bands of frequencies of sound (including ultrasound) that we

cannot hear, and there are examples of animals which have a much broader hearing range than

us. This shows that the human ear is tailored to pick up a certain frequency range. Shown below

is a scale in which sound is split up into infrasound (extremely low frequency) audible sound and

ultrasound (higher than human hearing). As we can see from this scale, compared to the total

range of frequencies of sound, the human hearing range only covers a small percentage of the

total range, since ultrasound starts at 20 kHz (20,000 Hz) and goes all the way up to and above

1GHz (1000000000 hertz).

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The Human Ear

The way in which the ears receive and process sound is a fascinating and complex mechanical

process which occurs in a number of steps (showing how quickly our brain can process the

information that we receive from our senses) the first of which involves the sound actually

hitting the outer ear. The shape of the outer ear (shown below) is such that it acts to collect and

channel into the middle ear and it is its shape which helps it to perform this function, this shape

is such that sound from a large range of directions (including directly behind you) will be

channeled into the middle ear. The concha and Pinna work so that sounds from different

directions and distances are not just received at the ear as the same piece of sensory information,

meaning that even if two sounds from different sources are of the same frequency, you will more

than likely still be able to differentiate between the two sound sources. Once a sound has reached

the outer ear, it will be channeled into the ear canal by the Concha, where it will then travel

down the ear canal and interact with the eardrum in the middle ear.

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The middle ear is an air filled cavity which consists of the eardrum (also known as the tympanic

membrane) and three bones called the malleus, incus and stapes respectively. The ear drum is a

thin cone shaped membrane which is tightly stretched across the ear canal; it separates the

middle and inner ear from the outer ear, it transfers sound from the outer ear to the middle ear

through its vibrations. The sound wave hits the eardrum, which then vibrates periodically at the

same rate as the frequency of the sound, thus replicating it; it will also vibrate more or less

depending on how loud the sound is when it reaches the ear drum, this is why the name eardrum

is so fitting to it. The diagram below shows the layout of the middle ear.

Once the sound has passed through the ear drum it triggers the malleus; this tiny bone is

connected to the eardrum in such a way that when the eardrum vibrates this movement is passed

directly on to the malleus. The malleus then causes the movement of another tiny bone within the

middle ear called the incus which in turn triggers the movement of the third and final bone in the

middle ear, the stapes. These movements are transferred in such a way that the frequency volume

and spatial information that the wave carries are all preserved to then be passed on to the inner

ear.

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Situated in the ear are the cochlea, oval window, semicircular canals, Eustachian tube and the

auditory and balance nerves. These work together to relay the sound wave onto the brain in a

form which the brain can then process the information. Below is a diagram in which we can see

the layout of the inner ear.

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The cochlea is a spiralled, hollow,

conical chamber of bone, if this were to be stretched out then it would be around 3cm long, it is

the cochlea that the auditory nerve is connected to. The cochlea is filled with fluid and lined with

over 20,000 of these nerve cells; each of these varies slightly in length and also varies slightly in

how much resistance it will provide against the force of the fluid that passes over them. If the

waves of compression and rarefaction match the fundamental harmonic of one of these hairs it

will vibrate enough that this in turn causes it to release an electrical impulse which is then carried

down the auditory nerve to the brain. Depending on how energetic the vibrations are from the

point of triggering electrical impulses, the sound will be perceived as a higher or lower volume.

So from this it is possible to see how the ear can pick a range of frequencies and amplitudes,

however, it is not fully understood how these electrical impulses are then translated in to what

we hear by the brain.

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Hearing loss

Hearing loss can occur due to two main causes; conductive and sensorineural hearing loss.

Conductive hearing loss occurs due to sound being unable to reach the inner ear; this could be

due to a blockage or a buildup of fluid from an ear infection. It can also be caused by a

perforation in the eardrum, which rather than being a blockage, means the sound cannot be

transferred through the ear as easily as if the eardrum were not perforated. The other causes of

this type of hearing loss is an abnormal growth of bone in the middle ear which causes the inner

hearing bone (the stapes) to be less mobile and less effective at transmitting sound, this is called

otosclerosis. This type of hearing loss can be caused by loud noise, however, this will only occur

through a perforation of the eardrum, which would have to be very extreme noise levels and

therefore this type of hearing loss is less related to loud noises. Perforation of the eardrum due to

loud noise occurs because the pressure of the sound wave is too much for the ear drum to deal

with and the tightly stretched membrane will break, causing a perforation.

Sensorineural hearing loss occurs due to damage to the tiny hair like nerve cells within the

cochlea of the inner ear, the way these pick up sounds is explained above. It can also be caused

by damage to the actual auditory nerve itself. Whilst there are many causes of this type of

hearing loss such as Ménière's disease or acoustic neuroma, I will be focusing on how this type

of hearing loss can occur due to acoustic trauma.  Periods of exposure to loud noises can cause

the nerve cells within the cochlea to become damaged, reducing their ability to pick up the

frequency of vibration they normally receive or they can become jammed (this can causes a

ringing in a person’s ears since the nerve cell is sending electrical impulses through the auditory

nerve). It is more common for this type of hearing loss to be related to exposure to loud noise

levels.

Both of these types of hearing loss can be prevented by either wearing proper ear protection or

by locating yourself at a point where the noise level is at its lowest, therefore reducing your

exposure to extreme noise levels.

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Research

There are a few methods of research which have been employed to achieve the results of this

project, and I will outline the methods used and why I chose to use these methods. Firstly, I

would like to explain the two methods of research used within this project; these being primary

and secondary research.

Primary research involves the collection of data relevant to the subject of research, this is

original information gathered for the purpose of the research in question. This can be divided

into two forms of primary research, qualitative and quantative research. Quantative research,

such as surveys, aims to gather information from many different sources to get an average view

of the topic. If only one survey were to be given to one person, that person might not fully

represent the public perception of a subject, whereas if this survey is given to many people, we

form a general view of what many people think; leading to information more relevant to the

public perception as a whole. This research always yields a more generalized view of the subject

in question, and as outlined above, can be good for things such as public perception of a subject.

Qualitative research, such as experimentation, and is usually relevant only to the particular case

studied. This research has its purposes as it can yield very accurate results about the particular

case that is being studied. Whilst this may not give insight into other cases, there are many cases

where a broad view is not needed and therefore testing one particular subject can give the results

needed. Often this is seen as a more scientific method of research; however, both these types of

research can yield valuable data to any subject if applied properly. For my project I have chosen

qualitative research as I aim to try and gain an overall view of public perception rather than a

specific case. I will also be using secondary research to support my primary research and to help

people understand the project as a whole.

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Secondary research is generally seen as information gathered from conventional sources, such as

peer reviewed experiments or published research. This type of research is vital to aiding in

backing up findings or results from primary research as these secondary sources of information

can be referenced in order to confirm the validity of primary research. Secondary research can

also be used by backing up points made with quotes from said research, especially if the

secondary research has results from tests which are considered to be valid. To this end my

project includes both primary and secondary research.

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Results

Question 1. At roughly what decibel level does damage to human hearing start to occur?

A. 0 dB

B. 80 dB – Correct answer

C. 30 dB

D. Don’t know

12

32

6

0 dB80 dB30 dBDon't know

As I expected with this question only 12 out of 50 people knew which decibel level causes

hearing loss or damage to occur, this confirms my hypothesis that people are not knowledgeable

about the subject. Whilst this may be the case over 3/5 of people actually chose 30 dB, meaning

that whilst they do not understand this subject properly, in theory they would choose much lower

dB levels than the threshold for hearing loss, meaning that they will avoid causing damage to

their hearing.

Just over 1/10 of people did not know, this combined with the error in judgment of the majority

of the survey group shows that awareness could be raised with regards to this matter and this

would be beneficial to trying to curb noise induced hearing loss.

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Question 2. What is the main cause of hearing loss?

A. Loud noise – Correct Answer

B. Ear infection

C. Poking things into your ear

D. Don’t know

Loud noise

Ear infection

Poking things into your ear

Don't know

0 5 10 15 20 25

Series1

Almost 50% of people answered loud noise with regards to this question, showing they

understand that noise exposure is the main cause of hearing loss that is prevalent throughout

society. Whilst I expected some people to understand this principle, more people than I expected

had knowledge on this subject.

Nearly 2/5 of people chose ear infection to answer this question. Whilst this is not the main

source of hearing loss, it is still quite a common factor, and so this shows some understand the

subject of hearing loss and how it occurs. 1/5 of people either answered poking things into your

ear or don’t know, these people probably have the least knowledge on the subject out of all of

my survey group and therefore shows that whilst awareness is higher than I expected, there is

still a large enough majority who need educating on the most common causes of hearing loss and

how to prevent it.

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Question 3.When listening to music through earphones, what volume level would you normally

have the music at?

A. Low level

B. Medium level

C. As loud as possible

D. Don’t know

No correct answer

Low level

Medium level

As loud as possible

Don't know 0

20

40

Series1

The idea of this question is to gauge how many people risk damaging their hearing by listening

to music through earphones at a high volume level. I was surprised to find that nearly 3/5 of all

people surveyed listened to their music at medium volume level, showing that they are not at a

high risk of noise induced hearing loss.

Whilst the majority of people listen to their music at a reasonable volume level, 1/10 of people

listen to their music as loud as possible. These people are most at risk to noise induced hearing

loss. Therefore, whilst a large majority of the public either understands the risk or simply listens

to music at a reasonable volume level, there is a minority of people who need more education

with regards to the risks they are running by listening to music as loud as possible through

headphones.

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Question 4. Which of these scenarios is likely to damage your hearing the quickest?

A. Normal conversation

B. Using a power drill

C. Standing near speakers at a concert - Correct answer

D. Standing near an idling bulldozer

1

9

37

3

Normal conversationUsing a power drilStanding next to speakers at a concertStanding next to an idling bulldozer

Nearly four fifths of all people surveyed chose the correct answer for this question. This shows

that in terms of what sounds can be the most damaging to the human ear, the people I surveyed

have more knowledge than I first hypothesized. Only a small minority of people think that one of

the other sources will damage hearing more quickly.

This shows that the public need informing less about this area than other areas which need more

addressing, this is useful in building an idea of the knowledge people have with regards to the

subject of hearing loss through acoustic trauma.

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Question 5.

How long does it take for hearing damage to begin if you are listening to music through

headphones at a high level (around 100 dB)?

A. 4 days

B. 8 hours

C. 15 minutes – Correct answer

D. Don’t know

5

13

18

14

4 days8 hours15 minutesDon't know

Around two fifths of people answered correctly, this shows that more people are knowledgeable

with regards to this subject than I hypothesized, meaning that the understanding with regards to

the subject is higher than I originally perceived. However, just over three fifths of people think

that the period is actually longer than 15 minutes or just simply don’t know how long it takes to

cause hearing damage in these circumstances.

So whilst more people are knowledgeable on the matter than I expected, a large percentage of the

people surveyed do have a lack of understanding or knowledge with regards to the subject. This

correlates with the fact that listening to music too loud is a major causes of hearing loss, since if

people don’t understand the levels of exposure they need to subject themselves to in order to

acquire some level of hearing loss, they are more likely to damage their hearing through listening

to music

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Question 6.

How do you most often listen to music?

A. Speakers

B. In ear headphones

C. External headphones

D. Don’t know

No correct answer, question is subjective

Speak

ers

In ear h

eadphones

Extern

al hea

dphones

Don't know

0

5

10

15

20

25

30

Series1

This purpose of this question was to discern what method of listening to music most people use,

as this would provide information which would be useful when the surveyed people answered

my next question. It also allows me to gain data on how many people are at a higher risk of

hearing loss due to the method they use to listen to their music.

Just under three fifths of people surveyed use speaker to listen to music as their primary source,

this means that less people than I expected are at risk of hearing loss through listening to music

through in ear headphones. I expected more people to use in ear headphones, and as such I am

surprised as to how many people do not use in ear headphones, meaning they reduce the chances

of noise induced hearing loss.

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Question 7.

If you were to listen to a sound at the same level using the methods mentioned in the previous

question, which method can most easily damage your hearing?

A. Speakers

B. In ear headphones – Correct answer

C. External headphones

D. Don’t know

Speak

ers

In ear h

eadphones

Extern

al hea

dphones

Don't know

05

1015202530

Series1

The majority of people seem to understand that in ear headphones cause the most damage to

hearing when at the same volume levels as the rest of the methods of listening to music. This

goes against my hypothesis that people do not fully understand the difference between listening

to music through different methods at the same volumes can cause varying degrees of hearing

damage/loss.

Just over 50% of people know that in ear headphones cause the most damage, showing that

whilst some people understand this risk, there are still other people who do not fully understand

or appreciate this. Around two fifths of people think speakers would be the main causes of

damage to hearing, showing there is defiantly a misunderstanding as to which method of

listening to music causes the most damage. To conclude almost half the people surveyed would

need educating with regards to this matter, as awareness on the subject is not high enough.

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Conclusions

The overall conclusions I can draw from my research are that for a start more information is

necessary to educate people as to how hearing loss occurs and what they can do to prevent noise

induced hearing loss. Whilst there is some knowledge, I feel this knowledge is patchy to say the

least and in every question there were people who did not understand the principle being

outlined. It may have only been a small percentage of people who misunderstood these

principles, but I feel it is a large enough minority to warrant more education of the public with

regards to the matter.

The results of the survey did not necessarily conform to all of the hypotheses that I proposed at

the start of the project, often in a positive way. I presumed that the public knowledge of the

subjects involved in hearing loss (especially noise induced hearing loss) would have been at a

much lower level than it actually is. This means that people have a larger knowledge base than I

first presumed and therefore more people than I expected know the causes and ways of

prevention of hearing loss.

I expected a lot of people not to understand the risks of in ear headphones and listening to music

through headphones at a high volume, since the statistics about hearing loss at the start of this

project state that hearing loss is on the increase and one of the main causes can be headphones

being too loud. Whilst this is related to younger people a lot of the people who I surveyed were

between the ages of 18-25 and therefore fall in the relevant category to the facts stated earlier,

there was a lot more knowledge with regards to the usage of in ear headphones and the volume

levels at which hearing loss is caused.

To summarize more people had more knowledge of the subject covered in this assignment as a

whole; however, there are enough people without relevant knowledge to lead me to believe that

increased awareness and education is necessary to curb the increase in hearing loss that we are

seeing in society.

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Evaluation

As a whole I feel the project has yielded relatively good results, although there are defiantly

areas of the project which could be improved. If it were possible, I feel testing peoples hearing to

see if they suffer from hearing loss before surveying them would have produced more conclusive

results and comparisons could be drawn between the answers people with hearing loss gave and

the answers people not suffering from hearing loss gave.

I also feel that if I were to perform the survey again, I might try to direct the questions more

towards testing people’s knowledge of how hearing loss occurs; I feel that the survey I

conducted was too general and could have been refined to produce results more relevant to the

purpose of the project. Less questions about decibel levels and what noise causes the most

hearing loss could be dropped in favor of questions more related to people’s knowledge of how

to reduce the impact of hearing loss and how to avoid it altogether.

I also feel that if I were to conduct the survey again, taking surveys of different age groups and

generally more people would help to make the results more easily interpretable, since we know

that age related hearing loss is a problem common amongst older people and we also know that

hearing loss is on the increase in the younger age groups. This would give results as to which

generations know more about hearing loss and could work to confirm the statistics given above,

it would also explain which age demographic needs educating the most and the most focus could

be given to this demographic.

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Glossary of Terms

Amplitude – The amplitude of a sound tells us how loud the sound is, the larger the amplitude the louder the sound. This is shown in the below diagram by the peaks of compression and rarefaction of the sound wave. These peak displacements represent the peak amplitude of the sound wave

Frequency - The frequency of a sound

wave is how often a full wavelength occurs within a certain time limit. The most basic definition

of frequency states that ‘Frequency is the number of occurrences of a repeating event per

unit time’ (reference this). Frequency is measured in Hertz (represented as Hz) and hertz can be

described as ‘The SI unit of frequency defined as the number of cycles per second of a periodic

phenomenon’ (reference). Shown below is a diagram depicting a single period of a sound wave.

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It would be best to describe frequency as the time it takes for one period to occur (a period can

be described as the time between one compression and the next compression following it); this

can be shown by a diagram of two waveforms of different frequencies, as shown below. Because

it happens less within the same amount of time compared to the waveform 2, waveform 1 is a

waveform of lower frequency than that of waveform 2.

Waveform 1

Waveform 2

Fundamental

frequency - The fundamental frequency is easiest to explain by using a tuning fork as an

example. When a tuning fork is struck, it will always vibrate at its resonant frequency, and the

same can be applied to any physical system. The example below shows two tuning forks (of the

same fundamental frequency), with hollow wooden bases, when one is struck the sound

produced by it causes the other to vibrate because both of the tuning forks have the same

fundamental frequency.

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Wavelength - Wavelength is directly proportional to frequency, but is the distance that a sound

wave covers within one period, rather than the time taken for this to occur. Wavelength can vary

greatly depending on the frequency of the sound, but within the human hearing range, all of the

frequencies can be measured in terms of metres (ranging from around 15m for a sound of

frequency 20Hz to 0.0015m for a sound of frequency 20 kHz). The higher a sound’s frequency is

the shorter its wavelength will be, meaning that when we get to ultrasound frequencies, the short

wavelength allows the wave to travel easily through mediums which lower frequency sounds

may not travel through.

Longer wavelength

Shorter wavelength

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Bibliography and references

http://www.physicsclassroom.com/class/sound/u11l2d.cfm - 21/3/12

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