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Ever wondered what sound is and how its created? Why deafness occurs? Or how noise cancellation headphones work? Even the reason for the headache you get from piercing noises? Every day we depend on our hearing to get us through daily activities, leisure, communication, work, and life itself. Although we are surrounded with sound and noise each day, most of us forget the incredible creation of these simple accesities. Sound is made up of vibrations that travel in a longitudinal wave where the particles move in the direction of the wave in a parallel pattern. These particles bump into each other as they transfer kinetic energy whilst the wave makes its way towards our ears. The sound wave is collected by the outer ear, moves into the ear canal and bumps against the eardrum. This vibrates the eardrum that affects the tiny bones in our middle ear. Vibrations of these bones hit a tube called the cochlea; these vibrations are then changed to electrical impulses which are called cilia that are attached to our auditory nerves. The cilia moves which in turn make the nerve cells react, sending signals to our brain through the auditory nerve. Our brain then interprets the sound as sounds or words we have heard before, but does not tell you the meaning of it; this is what listening is for.
Figure 1: How our ears interpret sound (Ref: http://www.learningthroughlisteningHYPERLINK "http://www.learningthroughlistening.org/Listening-A-Powerful-Skill/Listening-and-Learning/Benefits-of-Teaching-Listening/93/".org/Listening-A-Powerful-Skill/Listening-and-Learning/Benefits-of-Teaching-Listening/93/)
Sound waves can pass through solids, liquid, and gas. Sound transmits through solids the fastest as the particles can bump into each other easily and faster because of its solid form, compared to a gas where particles take longer to bump into another particle. This supports the fact that sounds waves are sound energy a form of kinetic energy where with energy the particles move faster transferring that energy, so the sound will be transmitted quicker.
Examples of kinetic energy are things that move, such as a rollercoaster's, a bouncing ball, or a bullet fired. If an object has kinetic energy, there are things within that object such as waves, atoms, electrons, and molecules that cause it to move. There are 3 types of kinetic energy; vibrational (energy as a result of vibrational motion), rotational (energy because of rotational motion), and lastly translational (energy due to the movement from one place to another). The amount of kinetic energy travelling faster depends on the weight and speed of an object. The faster and heavier an object is, it has more kinetic energy, compared to another object that may be lighter and slower.
Figure 2: Kinetic energy example (Ref: http://www.world-of-waterfalls.com/featured-articles-waterfalls-101-why-do-we-care-about-waterfalls.html)
This is the equation used to measure kinetic energy KE = ½ * m * v2. Here, m represents the mass of the object, and v represents the speed of the object. The faster the speed of the object goes, the more kinetic energy it will possess. This is the same for the density of an object. The denser an object is, the closer the atoms are formed together. When the energy passes through it is easier and faster through solids because the atoms are closely packed together in a way that transfers this energy from one particle to another.
Figure 3: Mass (density) and speed (velocity) of the equation for kinetic energy (Ref: http://www.patana.ac.th/secondary/science/anrophysics/unit4/commentary.htm)
Kinetic Energy Info (Ref: http://www.ifpaenergyconference.com/Kinetic-Energy.html)
Within a sound wave you will be able to identify a wavelength, frequency, and amplitude. The wavelength is used to measure how long a wave is till its next identical wave. The frequency tells us how many waves there are per second, this is measured in hertz. Lastly the amplitude of a wave will show us the air pressure, the range will start on the line where the wave comes up and stop on the highest scale measuring up or down. The amplitude is related to the volume of the sound you are listening to, as the amplitude is measured in the likes of its pressure. The higher the pressure, the louder the sound will be. Amplitude is measured in micropascals, but actual sound is measured in decibels. Hearing aids are made to amplify the noise of the surroundings you face each day, so people with the disability of hearing will be able to hear noises like other people normally with their hearing aids on as the volume will be increased in the mechanical device. An example of this will be the use of glasses; the lenses are especially made to prescriptions that meet the normal measurements of sight.
Figure 3: Features of a sound wave (Ref: http://library.thinkquest.org/06aug/02101/physics_soundwaves.htm)
The opposite creation of hearing aids would be noise cancellation devices such as earmuffs, ear buds, canal caps, headphones, etc. Nowadays we see the modern world full of life, busy, exciting and noisy. So it wasn't a surprise when pioneer Lawrence J. Fogel first came up with the concept of noise cancellation headphones to block out unwanted sound from the background and Dr. Amar Bose made the first set of headphones that advanced the technology. (Ref: http://en.wikipHYPERLINK "http://en.wikipedia.org/wiki/Lawrence_J._Fogel"edia.org/wiki/Lawrence_J._Fogel & http://en.wikipedia.org/wiki/Bose_Headphone_Family)
There are 2 types of noise cancellation, active and passive. Active noise cancellation is when you hear a sound and the device actively produces the same sound frequency 180° at the same time that is called anti-noise. When these 2 come together the anti-noise cancels out the real noise which will result in silence in the real world
Figure 4: Sum of wave's equal silence (Ref: http://www.school-for-champions.com/science/noise_cancellation.htm)
Some active noise cancellation headphones cannot always produce the anti-noise that exactly the same time and frequency. If this happens the sum of the waves will look somewhat like this;
Figure 5: Sound wave fraction of a second too late (Ref: http://www.school-for-champions.com/science/noise_cancellation.htm)
Passive noise cancellation is when the device is created with material that creates a sort of defence against sound by either absorbing or reflecting it. High density materials are layered over each other to provide the best form of passive noise cancelling this is a bonus for music headphones. Passive noise cancelling is less preferred because the materials are usually quite heavy and if there is too much it is uncomfortable to use.
Figure 6 & 7: Noise cancellation head phones and how they work (Ref: http://electronics.howstuffworks.com/gadgets/audio-music/noise-canceling-headphone3.htm)
Apart from devices made for leisure, on the market there are now items being made and sold to prevent people from damaging their hearing especially in working environments. These include ear muffs, ear buds and canal caps. The department of labour has recently made new requirements and reassessed their systems for work places with noisy environments such as factories, machineries, construction and building. A copy of these changes in appendix1 (Ref: http://www.osh.dol.govt.nz/order/catalogue/733.shtml)
Most items suggested by the Department of Labour are ones that passively cancel out noise, but which devices cancel out noise the most? Why do some materials only block out some noises? How do the materials absorb or transmit sound? There are many predictions and theories made to suggest what materials block sound the most, to possibly support or validate the theories of others and ourselves we will be answering these question in an independent experiment that aims to find out which materials cancels/reduces noise the most. We will do this by using 10 materials; wood, rock, sponge, metal, cotton wool, cardboard, polystyrene, plastic, and insulation. These materials were chosen for the different forms of density and mass; we set out to find out if these materials provide the best defence against sound or increase the noises we hear.
I predict that out of the 10 materials brought in to use for our experiment, materials like the insulation, cotton wool, sponge and polystyrene will be quite effective and successful in reducing the unwanted noise we will be producing. This is because these materials are of low density and the vibrations will be absorbed passively rather than reflected or transmitted. Having a lower density in a material will slow down the kinetic energy travelling through the material. In this case it will be the sound waves, the greater the mass of an object the faster or greater kinetic energy is being possessed or travelling. By absorbing the vibrations, items like these are known for its comfort and sound-proofing. An example of this is the insulation put inside walls whilst building or reconstructing a house, having insulation inside walls will help block sound waves yet keep the home warm enough with the energy absorbed by the sound waves.
Figure 8: Sound absorption (Ref: http://www.acousticalsurfaces.com/acoustic_IOI/101_7.htm)
Figure 9: Home insulation block out sound waves (Ref: http://eic-il-usa.com/insulation)
In this investigation we got into groups and did one big experiment together due to the lack of equipment and time. Our independent variable is the 10 different materials we are using; wood, rock, sponge, metal, cotton wool, cardboard, polystyrene, plastic, and insulation. Our dependent variable is the different graphs of the sound waves captured by the microphone. The control variables that we kept the same in this experiment is the ice-cream container that holds the materials, the microphone, the speaker, the frequency, time, amplitude, and wavelength of the sound produced, as well as the room we were testing in. By having these factors the same we are able to guarantee a fair test, and valid results. Like any other investigation, we have tested each material 3 times; to measure the waves, calculate an average, obtain accurate results, and make certain conclusions.
We found a room that would be silent and vacant for a long period of time, then we set up the speaker system on one end of a table.
On the other half of the table we put in our 1st material into the ice-cream container.
Then placed the container exactly 15cm away from the speaker, and had it standing like this;
Figure 10: Ice-cream container structure
- We marked a line so we did not have to measure each time we moved the container to put in a new material.
Behind the container, we measured 3cm and used a clamp to hold the microphone in place. We had the sensor facing the container's back.
Then set the speaker to ... Throughout the experiment we kept this sound the same, to make it a fair test as one of our control variables.
We connected the microphone to a laptop that has software called Logger Pro Version 3 downloaded and installed, then opened it up.
We were sure to have a new graph ready. By clicking into settings, ticked the box for repeat and preset the time to 0.05 seconds.
When everything was set, we put the speaker on, and then clicked the collect button on the screen of the laptop.
Patiently we waited approximately 3-5 seconds then clicked stop, we got a graph.
To make the graph larger, we clicked on a button called Auto scale, to enlarge the graph.
We saved it into a folder, named it the object we were testing so we did not mix it with any other graphs from this experiment.
This was done 3 times for the same material.
After the 3rd time, we took the ice-cream container and emptied the contents. Then inserted another material to test, and placed the ice-cream container at the same mark we made for 15cm.
We did this for all 10 materials so in total we collected 30 graph data's altogether.
We understood that it was very important that the room was quite at all times in this experiment as any other sound waves could have been collected by the microphone.
When all data had been collected, we packed up everything.
Later on we printed out all the graphs to label and photocopy for the rest of our team members.
We were careful to keep them separated from each other, if some graphs got mixed up with another material graph we would get results that would not be accurate, and the experiment will need to be repeated. For example, if a metal graph got mixed with a plastic graph the averages we get form measuring the waves would not be valid so these cannot be used for our results, experiment, or conclusion.
Lastly we measured the waves on our graphs by drawing a line and figuring out the most lines in the highest amplitude and the lowest, subtracted them and got our answer. This was done with 3 graphs for each material, to find our average we added the values from all 3 graphs, and divided it by 3. This is done to bring in our results and conclude this experiment.
Figure 11: Experiment layout
Results: Graphs seen in Appendix 2
Out of the 10 materials we have chosen to experiment with to find out which ones can reduce/cancel noise the best, we have chosen 5 main graph results to focus on; plastic, polystyrene, metal, insulation, and sponge. All these materials have similar as well as different structures, substances, density, mass and weight. This is ideal for our main aim to find out what material cancels or reduces noise the best, and will either support or bring in new predictions towards our hypothesis and the theories of other sources.
After carefully measuring the different graphs, rounding them up to the nearest point, and finding out their averages. We have come to realize that within the 5 materials we have chosen, plastic is the worst at reducing sound with amplitude of 0.013, then comes metal with 0.011, after metal we see polystyrene and insulation not too far off both measured with amplitude of 0.010. Lastly our most successful material was sponge, just slightly topping both polystyrene and insulation with average amplitude of 0.009.
In our results we see that all the amplitude averages were not too far out of reach from each other, they are all seen one or two points away from one another's material amplitude. This tells us that this is a valid experiment that was done in fair conditions and came up with reliable results. If we were to have results that are extremely different to what we have now, such as 10 point difference these would not be results that can be relied on to gain an accurate conclusion as they do not match any other averages and show no trend. Our only option would be to redo our experiment, and have recount where we might have gone wrong.
There were only 2 materials that were in the exact same range as one another; the insulation and polystyrene. This did not come as a surprise to me as I suspected that they would fall in the same scale because of the similarities in the aspects of their materials. Both these materials have been known for their use in energy conservation and thermal resistance. They are formed in a way that protects something or someone, blocks sound waves to provide noise control, and warm its surroundings. This is why nowadays we can see them combined together to produce the best kind of protection. Appendix 3
(Ref: http://www.energysavers.gov/your_HYPERLINK "http://www.energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11580"home/insulation_airsealing/index.cfm/mytopic=11580)
Differences between Each Trial of All Materials Measured In Percentages Compared To Plastic (Our Highest Value in Our Results)
Total Graph Average
Total Percentage Average
In the table above we can see that the differences of reduction between sponge and an empty container compared to the effect of plastic have a great percentage of differences. Compared to plastic, sponges and a vacant ice-cream container reduce 36.65% more noise than plastic can. This makes them approximately 1/3 more reliable then plastic in blocking out sound waves. Next we have both polystyrene and insulation coming to a total of 29.15% in succeeding to reduce sound compared to plastic (26.6+30=56.6 /2=28.3 +30=58.2 /2=29.15). This is approximately higher than 1/4 of plastic's effect on the sound waves collected. Lastly the material that does not have a significant change to the impact plastic made is metal, with only an 18.3% difference between plastic and metals reduction of sound (metal approximately 1/6 better at reducing sound then plastic) these 2 materials are our worst at decreasing the noise we hear.
Between our best and worst sound reducing materials, plastic and sponge has only a .004 point difference but on the scale of intensity there is a 30% difference on the reduction of sound. This tells us that even though these two items have different appearances, textures, volume and mass. They have some identical qualities in the material that block sound waves in a similar pattern.
In conclusion, I think that our worst sound reducing materials like plastic and metal resulted last in our results because it relates back to the equation of kinetic energy. The denser our material the faster sound energy travels. Plastic and metal is our most dense materials compared to insulation, sponge, and polystyrene (polystyrene did not fill up the whole ice-cream container, my prediction is that in total plastic would have been denser compared to the polystyrene). Therefore the sound waves passes through these materials slower with barriers in the way. With the metal and plastic it speeds up this process because of the atoms in these materials closely formed together.
Although metal is denser than plastic, plastic did a worst job at reducing sound. This is because the metal we used in this independent experiment was from parts of a car, bolts and nuts that were singular and small piled up together. A huge factor that influenced the results we collected was the fact that the individual metals were sealed tightly in a glad wrap when put into the container. The overall amount of metal only reached an approximate halfway mark in the ice-cream container and would have weighed down when the container was prompted upwards as seen in figure 8: ice-cream container structure. The sound waves had a lot of air space to pass through in between the different bits of metal, and kinetic energy travels slower in air then in solids, this is why I believe that metal came 2nd in our worst materials list. If a large chunk of metal with no holes, or missing parts was used I strongly believe that metal would be our worst material to reduce sound as the sound wave have no barriers to slow it down or be absorbed, the particles would be tightly held together and rub off energy from each other easily with speed, and the density of the metal supports the speed of sound with kinetic energy.
Relating back to our table above, within our trials, our major differences are insulation and plastic (0.013-0.006) and insulation/sponge compared to plastic (0.013-0.013). Our first trial of insulation told us that compared to plastic insulation has a 70% difference in the reduction of sound, this is a staggering fraction of 5/7 better reliability. Another notable change was insulation and sponge's 3rd trials both measured 0.013 in exact with the value we are comparing it to which is the plastic. This means for these 2 trials they gain no differences in the performance of reducing sound compared to plastic. I think these graph data's collected was not accurate, because of the other trials' results we can see that they vary in difference. For example; insulation's 1st trial resulted in 0.006, 2nd trial 0.011, and last trial 0.013. Within these results the differences between each one collected reach as high as 5. I believe that this is a sign of something we may have done wrong or different with each trial. Such as everyday background noises could have been collected by the microphone analysed in the results. During the experiment, we had quite a few people in the room so other background sounds like someone eating, a door closing or the sound of typing on a computer could have easily been collected by the microphone if the sound was in close range.
Furthermore our average sound pressure for an empty ice-cream container is 0.009; all our other results we have collected show us that these materials actually increased the amplitude of the sound we produced. There are no materials that reduced the sound, instead we see that sponge has the same sound pressure as our empty container, as for the rest they steadily increased the volume of our sound making it louder than before after going through the materials in the container. Our best bet on a noise reduction material (within the range of the materials we tested) will be the sponge. Even though our average from all 3 trials shows us that sponge did not increase or decrease our amplitude of sound, it has the lowest sound pressure with a difference of .001 out of the 5 materials we tested. Sponge's minimum mass/volume could be the reason for this; we had approximately 5 sponges in the ice-cream container this left space for air between each sponge, so even if the sponge absorbs some of the sound waves and converts them to heat energy there are air spaces in the container that transmits the sound through the container and into the microphone. Refraction of sound waves could also be another reason.
Refraction of sound waves is the change of direction these sound waves travel at when passing through one medium to another, this changes the speed/velocity of the sound waves. In our experiment when the sound waves reach the container, they pass through but at a different speed I predict it will be faster. With this new speed the direction gradually changes too, the new speed of sound waves in air is determined by the temperature on the surface, with this equation (c=331 + 0.6 T) where T is the temperature in degrees. For example if the air is cooler down on the ground sound waves travel slower here compared to a temperature containing heat above the ground supplying speed to the sound waves produced. This is called a temperature inversion, and supports our sources for kinetic energy. In our case, when the sound was being collected by the microphone the sound waves could have turned a new direction and gained a new speed due to the temperature of the room and the conversion of absorbed sound waves to heat energy.
Apart from refraction and air spaces, other aspects of our investigation could have influenced the results we attained and the overall conclusion towards this experiment. We cannot be certain about the accuracy of this experiment; even if we have tried to add a fraction of reliability towards this experiment by having collected 3 different graph data's for each material. The way we measured our graphs, calculated our averages and noted our changes are all done independently, so our results may vary from the same experiment. Possible ways to improve our overall investigation would be to collect more readings of our graph data's for each material so we can be certain that our results can be relied on. Repeat our experiment a couple of times, to gain a higher level of accuracy and to encounter any errors or new sets of data different to the ones we have collected now. By repeating our experiment we can also support, back-up or change our current information to suitable address our results. As well as compare the new graphs to the ones we current have now, to identify any new leads or unnoticeable disruptions in our first experiment. We could also make sure the quality and quantity of our materials are within fair variables, all the same amount (fill up the whole ice-cream container), no air spaces, etc. By doing this we might actually gain results that reduce, absorb and reflect sound.
Weak areas of our experiment include our set up, the measurements of the microphone, and the placement of the ice-cream container away from the speakers. We only allowed a 3cm gap between the back of the ice-cream container and the sensor of the microphone. This is not ideal if possibilities of refraction occur as the microphone would not be able to move in directions the sound waves are travelling in. We could place the microphone further away from the container around 10-15cm to eliminate chances of refraction. The ice-cream container we used was also a limiting factor to this experiment, instead of using an ice-cream container to hold the materials we are testing we could have measured the sound waves directly on or a few inches away from the material itself to improve our accuracy when measuring our amplitudes, averages, changes, and writing up our conclusions. Having the ice-cream container placed in the position and distance it was in this experiment, gives us less accountable results and arises question as to why a particular material does better/worst than expected. In overall evaluation, the method we used in this experiment has seen success in bringing the results we were expecting as well as those we did not. With the limited time, resources and planning we had I can confidently say that this investigation have been completed to the best of our abilities.