Download Background Research

Meet The Team
Ella Lyons is our team leader. Whilst we were
doing our experiment Ella was the main
operator of the data logging device. Ella took
charge in any part of our experiment which
involved computers or machines.
Jessie Nolan took responsibility for doing the
research for our project. She studied work done
by other scientists on this subject and found
out lots of background information on our
topic.
Emma Russell was in charge of updating our
blog for our project. She frequently went online
to our blog and put up posts and information
about how our project was progressing.
Summary
Our science project is an investigation into the varying levels of
damage that different types of earphones and mp3 players cause to
hearing. We wanted to find out whether different portable music
devices and different styles of earphones cause varying amounts of
damage, and then find out which were the most / least harmful.
In order to carry out our investigation, we carried out an
experiment using a sound sensor and data logging equipment. We
tested sound level intensity (in decibels) of five different styles of
earphones, and four different portable music devices. The higher
amount of decibels each subject produced, the more damage it
would cause to a person‟s hearing. The controls in our experiment
were; the song played, the length of time it played for, the volume
of the device. When we were testing the different earphones, the
music device remained constant, (we used an iPod touch, as it is
the latest and most popular music device we were testing) and
when we were testing the music devices the earphones remained
constant (we used Apple earbud earphones as they are the most
commonly used earphones).
A graph was drawn by the data logger for each subject we tested,
and when we had finished testing we examined and compared all
of the different graphs to find out which device and earphone style
were the most harmful (i.e. had the loudest sound level intensity in
dBs) and which were the least harmful (had the lowest sound level
intensity in dBs).
From doing this experiment, we came up with the result that the
most harmful device is the Alba discman, at 102 dBs (the
equivalent of a pneumatic drill) and the least harmful device is the
iPod nano chrome with a sound intensity level of 93 dBs. The
earphones that are capable of causing the most damage are the
Sennheiser MX 350 earphones, which have an earbud design.
Their sound level intensity was 99 dBs (the same level as a
chainsaw) the earphones that are least damaging are the Goodmans
headphones with a “muff” design. These have a sound intensity
level of 80 dBs. These results brought us to the conclusion that
different music devices and different earphones do, in fact, cause
varying levels of damage; with earbud earphones and the Alba
discman causing the most damage, and muff style headphones and
the iPod nano chrome causing the least damage.
We feel that this research could be very interesting to many people,
especially to teenagers of our age who listen to music through
earphones a huge amount. If more people knew about the damage
earphones and personal music devices are causing them, they
would probably do a lot more to try and prevent this damage from
occurring. And the results we have obtained in regards to which
earphones and devices are least harmful will enable people to make
informed decisions about which portable music devices, and which
earphones to buy.
Introduction
Our hypothesis is that earphones have a harmful effect on people‟s
ears. We wanted to find out whether different types of earphones
cause varying levels of damage on peoples‟ ears, and we also
wanted to test whether different music devices (ipods, walkmans
etc.) cause varying levels of damage.
Our group found this topic very interesting because teenagers of
our age have a great interest in music. The vast majority of our
peers have some form of personal music device such as an ipod
etc., and we all spend a great amount of time listening to them
through earphones. For this reason, we wanted to see if these
earphones are causing us damage.
In order to carry out this experiment a certain amount of research
had to be carried out. We searched the internet for previous studies
that had been carried out by other scientists on this subject. We
were looking to further develop our hypothesis and we found that
many people have researched and experimented on this topic.
Almost all of the people who researched this topic discovered that
earphones are, in fact, harmful to peoples‟ ears. This information
made us even more curious to see whether the type of earphones or
music device affected the damage caused.
We were very fortunate that the science department in our school
recently got new data loggers and sound sensors so we used these
in our experiments to test and compare various earphones and
music devices.
Background Research
When at first we thought of the idea for our project, we
planned on investigating whether or not listening to music
through earphones from a portable music device could
damage a person‟s hearing. However, upon researching
previous studies of this hypothesis on the internet, it
became blatantly obvious that earphones did in fact cause
damage to hearing, as has been proven by a huge amount of
people in recent years.
On seeing this, we felt it would be somewhat redundant
trying to investigate something that has already been
investigated and proven so many times before, so we began
to think of different aspects of this topic that we could
research.
Although the vast majority of our peers own personal
music devices, we realised that no two people have exactly
the same thing. There are many popular music devices out
there, such as different styles of iPod, walkmans etc, and
there are so many different types of earphones available,
too. So, we set out to investigate which portable music
device can cause most damage to the ears, and which type
of earphones are most damaging also.
How Hearing Loss Happens
The diagram shows a simple version of how human hearing
works. Sound travels down the ear canal and causes the ear
drum to vibrate. In the middle ear, a bone attached to the
ear drum vibrates with the ear drum and generates sound
waves through the middle ear, which causes another bone
to vibrate against the cochlea of the inner ear. The cochlea
is filled with fluid and is lined with hair cells that are
sensitive to frequency and convert vibrations into electrical
signals going to the brain.
This is a table produced by OSHA; the European Agency for
Safety and Health at Work. It shows how long it takes for damage
to occur to a person‟s hearing when listening to sounds at varying
levels.
Sound level
Time taken for damage to occur
90 dB
8 hrs
92 dB
6 hrs
95 dB
4 hrs
97 dB
3 hrs
100 dB
2 hrs
102 dB
1.5 hrs
105 dB
1 hr
110 dB
0.5 hr
115 dB
0.25 hr or less
The table below shows how many decibels various sounds are, so
you can have an idea how loud these decibel levels are.
60 dB
Everyday conversation, ringing telephone.
70 dB
Restaurant.
80 dB
Heavy city traffic, alarm clock at 2 feet, factory noise,
vacuum cleaner, garbage disposal.
90 dB
Subway trains, motorcycle, workshop tools, lawn
mower.
100 dB Chain saw, pneumatic drill.
110 dB Dance club.
120 dB
Rock concert speaker sound, sandblasting,
thunderclap.
130 dB Jet take off, gunfire.
Common Types of Hearing Damage
Sensorineural Hearing Loss
Sensorineural hearing loss occurs in the inner ear when high
energy sound waves are too powerful, and kill hair cells. When
hair cells for a band of frequencies are destroyed, those frequencies
can no longer be heard. High frequency hair cells are the most
sensitive, so it is most common for people to be unable to hear
higher frequency sounds.
Tinnitus
Tinnitus happens when the hair cells are damaged beyond repair.
Tinnitus is when the damaged cells fire continuously, even though
there is no actual sound. It is described as a constant loud buzz in
the ears at the frequency of the hearing damage. It is not currently
curable, but there are devices and treatments available to reduce
the impact on the sufferer.
Headphones vs. Loudspeakers
When sound is played out of a loudspeaker, the sound must travel
through the air before it reaches the listener‟s ears. By the time the
sound reaches their ears, a lot of the more harmful high frequencies
have been absorbed by the air. When listening to music through
earphones, there is no time for any of the frequencies to be
absorbed by the air, as the earphone is literally pressed into the ear,
so the ear hears all frequencies, which causes much more damage.
Did You Know…
What you are doing while listening to music also has an affect on
the damage caused. For example, if you are listening to your iPod
while walking along a busy road, you are more likely to suffer
damage by turning up the volume to compete with the noise
around you. Also, listening to your iPod while exercising causes
more damage, because during aerobic exercise blood is diverted
from the ears to the limbs, leaving the inner ear more vulnerable. A
Swedish study suggests that your risk of hearing loss is doubled
when listening to music during exercise.
Symptoms of Hearing Loss
Some people are caused so much damage by listening to loud
music through their earphones that their hearing can be severely
affected. There are some early symptoms of this damage which
would indicate a trip to the doctor is needed to prevent permanent
damage. Below is a list of some symptoms a person may
experience if they are suffering from hearing damage:
 Ringing or buzzing in the ears.
 Difficulty in understanding speech
 Slight muffling of sounds
 High sensitivity to poor acoustics
Experimental Methods
Apparatus required: Data logger
Various sound devices
Various types of headphones
USB stick.
Method
1. Prepare the data logger for the experiment. Open a „sound
level (dBs) vs. time (s)‟ graph.
2. Prepare the sound device and set of earphones so that there
are no overlaps or confusions.
3. Firstly, test the different types of earphones.
a. For each set of earphones tested, play a certain song for
exactly one minute. Make sure to use the same device
for all the different sets of earphones and play the same
song.
b. Hold the earphone exactly 1cm away from the sound
sensor and start the music and turn on the sensor.
c. The data logger will draw up a graph of the sound
intensity for the minute.
d. After one minute of testing one set of headphones, stop
and save the graph. Then open a new graph for the next
set of earphones.
4. The next bit of the experiment is to test the different devices.
a. The same process is used to test the devices.
b. Play the same song for one minute on each device.
c. Pick one set of earphones to use for all of the devices.
d. Hold the earphone 1cm away from the sound sensor.
e. Again, the data logger will draw up a graph for the
sound intensity of the device.
f. Save every graph after each device and open a new one
for the new device.
Earphones
There were 5 different types of earphones that we tested. They
were:
1. Sennheiser MX 350
2. Apple Earbud Earphones
3. Sennheiser MX 460
4. Philips
5. Goodmans Headphones
All of these earphones produced a different result for us so it made
it easy to distinguish which one was worst for your ears.
Devices
We tested 4 different types of devices for this experiment. Since
most teenagers listen to Apple iPods we decided that most of our
devices would be different brands or types of iPods. Our order of
testing them was:
1. Discman
1. iPod Touch
2. iPod Nano Chrome
3. iPod Nano (1st generation)
Even though three of our devices were the same brand, our results
were still quite different so we were still able to find an accurate
result of which device was worst for your ears.
Controls and Variables
Testing the Earphones
The controls in this experiment were the sound device, the song,
the time the music was played for and the distance the earphone
was held away from the sound sensor.
Whereas the variables in this experiment were the different types
of headphones.
Testing the Sound Devices
The controls in this experiment were the set of earphones used
(Standard apple earphones were used because as research shows,
these are the most widely used earphones by teenagers), the song
played, the time the song was played for and the distance the
earphone was held away from the sound sensor.
The variables in this experiment were the different types of
devices.
Results
Earphone Results
Most Harmful Earphones
Five graphs were drawn for the five sets of earphones tested. In
order to figure out which earphone causes the most damaged, a
reading was taking of the sound intensity for each pair.
The most harmful earphone was the Sennheiser MX 350
earphones. The sound intensity for these headphones was 99 dBs.
This would be the same level of sound as a chain saw. If you were
to listen to music at full volume through these earphones, it would
take only about two straight hours for damage to start occurring to
your ear.
Sound Intensity for Sennheiser MX 350 Earphones
Least Harmful Earphones
The least harmful pair of earphones is the Goodmans Headphones.
Because they are a headphone, they do not sit inside the ear.
Instead they sit on top of pinna (the fleshy part of the ear). This
would mean that not all of the sound frequencies produced go
directly into the ear. As a result of this, the sound intensity will be
lower. The Goodmans Headphones had a sound intensity level of
80 dBs. The difference between this pair of headphones and the
worst pair (Sennheiser MX 350) is 19 dBs. As studies show, this
difference would mean it would take eight straight hours longer
before listening to music at full volume would start causing
damage to ears.
Sound Intensity for Goodmans Headphones
Device Results
Most Harmful Sound Device
The Alba Discman is the most harmful sound device that was
tested. It produced a sound intensity level of 102 dBs. This is the
same as listening to a pneumatic drill. The hypothesis said that this
device was most likely to be the worst device because it is so old.
New regulations were only brought in last September. This device
is over ten years old so no proper regulations were in play when
this device was brand new. This supports our results.
Sound Intensity Level for Alba Discman
Least Harmful Sound Device
The least harmful device tested was the iPod Nano Chrome. The
sound intensity level for this device was 93 dBs. This is 9 dBs
lower than the most harmful device but it still isn‟t low enough not
to cause damage. Music at this intensity level will begin to cause
damage after about six straight hours. This result did not support
the hypothesis as it stated that the iPod Touch was most likely to
cause the least damage as it is the newest model of the iPod but
this was not the case. The iPod Touch was only 6 dBs higher but
this could shorten the amount of time before damage begins to
occur by 3 hours.
Sound Intensity Level for iPod Nano Chrome
Conclusion And Recommendations
Based on the data we collected from our experiment using the
sound sensor and data logging device, and the background research
we have done, we have come to the conclusion that earphones can
cause severe damage to hearing. We have also concluded from our
testing of various devices that different portable music devices
cause varying levels of damage.
These conclusions support our hypothesis. Our hypothesis stated
that hearing is damaged by listening to music on portable music
devices through earphones. It stated that different devices and
different earphones cause varying levels of damage, and that the
older devices such as the Alba Discman would be more damaging
to hearing than newer devices which were produced after
legislation was put in place to limit the sound intensity level of
personal music devices. One thing which did not support our
hypothesis is that the least damaging device was the iPod Nano
Chrome. Our hypothesis stated that the least damaging device
would be the iPod touch, as it was the newest device that we
tested.
We tested 5 different types of earphones and 4 different music
devices. From this testing we concluded that the most harmful
personal music device is the Alba Discman, which has a sound
intensity level of up to 102 dBs, and the least harmful device is the
iPod Nano Chrome with a sound intensity level of up to 93 dBs.
The most harmful earphones were the “earbud” style Sennheiser
MX 350 with a sound intensity level as high as 99 dBs, and the
least harmful were the “muff” style Goodman‟s headphones, with a
sound intensity level up to 80 dBs.
Recommmendations
We felt that our investigation could have been improved if we had
been able to test a larger variety of devices and earphones. It also
would have been helpful if we had been able to pinpoint the date of
production of each subject so we could examine visible trends of
whether more current ones were less harmful.
Acknowledgements
We would like to give a huge thank you Colleen Livingston who
took great interest in our project and experiments. Colleen is from
Michigan and is on an exchange program in our school. During her
time here she has taken part in different aspects of our Scifest
project; most notably helping put together our poster display.
We would like to thank our science teacher Ms Greehy, who
supervised our work. As she is our main science teacher she
entered us into Scifest and helped us with our project when we ran
into difficulty.
Mathew Lyons who is Ella‟s brother taught us how to use the data
logger as no one on our team had ever used one, so it was a great
help.
Mr. Ward, the physics and computer teacher in our school helped
us set up our blog on projectblogger.com to keep an account of the
work we were doing.
Thank you to the science department in our school who allowed us
to borrow a sound sensor and data logging equipment in order to
carry out our experiment.
Our final thank you is to all the girls in our year who lent us their
iPods and walkmans to test. We couldn‟t have done our
experiment without them.