Block That Noise!

Background Information for Teachers

Sound waves are vibrations that travel through the air and are detected by the human ear. These waves can be reflected, absorbed, or transmitted through various materials (Figure 1).

Image Credit: Ben Finio, Science Buddies / Science Buddies
Figure 1. Reflected, absorbed, and transmitted sound waves.

For example, you hear an echo when sound waves are reflected off the walls in a large space. Sound waves can be absorbed by soft materials like carpet or ear protectors. They can also be transmitted through solid materials, which is why you can hear someone yelling through the wall in another room. Materials that absorb sound waves are called sound insulators.

The loudness, or intensity, of sound is measured in decibels (dB). Figure 2 shows the decibel ratings of some common sounds. Decibels are a logarithmic scale, not a linear scale. That means that for every increase of 10 dB, the intensity doubles. For example, a chainsaw (100 dB) is much more than twice as loud as moderate rainfall (50 dB). Sound levels above 80 dB can cause hearing damage over long periods of time, and sound levels above 120 dB can cause immediate damage.

Image Credit: Ben Finio, Science Buddies / Science Buddies

A bar graph highlights decibel levels of common sounds from the loudest at the top to the softest at the bottom. A gunshot is the loudest common sound with a value of 140 decibels, a normal conversation has a value in the middle of the graph of 60 decibels, and the sound of breathing is the quietest with a value of 10 decibels.

Figure 2. Decibel levels of some common sounds.

In this lesson, your students will build sound-insulating containers big enough to put a phone inside. To test how well the containers dampen noise, the phone will measure sound levels using a sensor app that is able to record data from your phone's microphone and displays it in a graph. Figure 3 shows two graphs recorded with a phone placed in front of computer speakers playing white noise. With no insulation, the average sound level was 40 dB (left), but with the phone placed in a bag of cotton balls, the average sound level dropped to 10 dB (right). Remember that a decrease of 10 dB means the sound is half as loud.

Image Credit: Ben Finio, Science Buddies / Science Buddies

Example graph of sound intensity over time shows a line that is constantly fluctuating due to a noisy environment. The average sound measured is about is 40 decibels.

Image Credit: Ben Finio, Science Buddies / Science Buddies

An example graph shows sound intensity over time in a very quiet setting. The measured noise does not fluctuate above or below 1 decibel, but there are small and constant changes that indicate it is not completely quiet. The average sound measured is about 10 decibels.

Figure 3. Comparison of noise levels before and after insulating the phone from sound.

In this project, your students will follow the engineering design process. The engineering design process is an iterative process where students design, build, and test their containers. It is important for students to understand that there is no single "right answer" to an engineering project. There are multiple possible solutions to the problem, and it is OK if their containers do not work very well on the first try. Part of the process is redesigning, rebuilding, and retesting your container based on what you learn from your initial tests.

Additional Background Links

• Decibel Exposure Time Guidelines, Dangerous Decibels
• Sound Waves and Music, the Physics Classroom
• The Engineering Design Process, Science Buddies
• Comparing the Engineering Design Process and the Scientific Method, Science Buddies
• Decibel Scale, Kahn Academy (video)

Prep Work (20 minutes)

Make sure you are familiar with the sensor app you are using before you show it to your students. The best way to do this is to play with the app on your phone to get comfortable enough using it to explain it to your students. Ideally, you want to test the experiment yourself with the app before class to make sure it works as intended.

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To set up your classroom for the lesson:

• Lay out the assorted construction materials so the students will have easy access to them.
• Set up a single testing station, as shown in Figure 4, where students can come to test their sound-insulating containers.
  • The test station should have one phone equipped with the sensor app, and a second phone, tablet, or computer with speakers.
  • The second phone/tablet/computer will need a way to play a sound at constant volume, such as a white noise app or website (search online for "free white noise player"). This will work better than playing music since the volume of a song can fluctuate too much. You should set the volume so it is noticeably louder than ambient noise in the classroom, and make sure no one adjusts the volume once you start the activity.
  • It is important that the distance between the sound source (e.g. speakers) and the containers remain constant, since sound intensity decreases with distance. Use masking tape to mark an "X" where students must center their containers, and a boundary area that their containers must fit inside. Make sure the speakers do not move (tape them down if necessary).

Image Credit: Ben Finio, Science Buddies / Science Buddies
Figure 4. Example testing area.

Engage (15 minutes)

Optional: the accompanying slideshow contains information and graphics to help lead a classroom discussion with your students.

1. Ask your students to think about sound waves and different scenarios where they are reflected, absorbed, or transmitted.

   What are sound waves?

   Sound waves are vibrations that travel through the air and are detected by your ear. The stronger the vibration, the louder the sound.

   What are some examples of sound waves being reflected?

   One example is when you hear an echo in a large, empty room like an auditorium.

   What are some examples of sound waves being absorbed?

   One example is when you wear earplugs or earmuffs to protect your ears from loud noise.

   What are some examples of sound waves being transmitted?

   One example is when you can hear someone yelling through the wall from an adjacent room.

   Is sound always completely reflected, absorbed, or transmitted, or can it be a mix of the three?

   Sound waves can be partially reflected, absorbed, or transmitted through a material. For example, when you wear ear muffs, you can still hear loud noises, but they sound quieter than they would if you were not wearing the ear muffs. The sound waves are only partially absorbed by the ear muffs, and the rest is transmitted to your ears.

2. Ask your students to think more about sound insulation and decreasing the loudness of a sound.

   What do you do to avoid loud noises or sounds you don't like? For example, if someone is playing loud music or an ambulance drives by with the siren on?

   Examples include covering your ears with your hands, covering your head with a pillow, or wearing earplugs.

3. Explain that sound is measured in decibels. Explain that if the number of decibels doubles, the loudness more than doubles. For example, a chainsaw (100 dB) is much more than twice as loud as moderate rainfall (50 dB).
4. Introduce the sensor app to your students, specifically the sound sensor (audio amplitude in phyphox). Remember that when using the phyphox app you will have to calibrate the audio amplitude sensor together with your students before they do any measurements. Do this calibration together as a class before you start your investigations, so each device has comparable sensor readings. Remind students that they will have to recalibrate their sensor every time they start a new recording!
   1. When using the phyphox app, open the audio amplitude function, calibrate the sensor (set the decibel offset), and press play to start a recording. Show the graph to your class.
   2. Let them watch how the graph fluctuates as people move around, talk, or make noise.
   3. See how low they can get the graph to go if everyone sits perfectly still.
5. Explain that in this project, their goal will be to design a sound-insulating container. The phone will be placed in the container during testing. Testing will involve placing their container a fixed distance from the speakers playing at a constant volume, then using the phone and app to measure how much the sound diminishes inside the container. They will have time to design and test their devices before a final competition. There are a few rules they must follow:
   1. Their container must fit completely inside the box marked in the testing area.
   2. They must use only the materials you have provided.
   3. The container can completely enclose the phone, but they must be able to easily remove and insert the phone (do not permanently tape the phone inside a box).
6. Finally, explain that the engineering design process is iterative. There is no single "right answer" to the problem, and their device might not work well on the first try. This is OK and just like real-world engineering. They will be allowed to build, test, and redesign their devices as many times as they want within the time limit.

Explore (75 minutes)

Design, Build, and Test Phase (45 minutes)

1. Have each group of students cut out a piece of corrugated cardboard the same length and width as the phone you will use to test. They can use this to make sure the phone will fit in their sound-insulating container.
2. Ask each group to spend 5 minutes brainstorming a design for their sound-insulating container before they start building. What materials will they use? How will they put it together? You can use the student worksheet for students to write down ideas and make sketches of their designs. Remind them about the rules listed above.
3. Allow students to gather materials and start building their containers.
4. When individual groups are ready, they are allowed to come to the testing station to test their container.
   1. When using the phyphox app, open the audio amplitude function and calibrate the sensor by re-setting the decibel offset. Then press the play button to start a recording.
   2. Place the phone inside your sound-insulating device.
   3. Place the sound-insulating device on the marked spot at the testing station.
   4. Play white noise through the speakers at a constant volume for a fixed amount of time (for example, 10 seconds).
   5. Stop the white noise.
   6. Remove the phone and press the pause button to stop the recording. Make sure to save your data.
   7. There may be very noisy data at the beginning and end of your trial, when you were putting the phone in and out of your container. Use the pan and zoom feature to zoom into your graph, so the trial only shows the section in the middle where you played white noise at constant volume as shown in Figure 5.
   8. Record the average decibel value for your cropped trial. You will need to export your data from the app to determine the average decibel values of your recordings. You can either export your data as a .csv or Excel file. Open the exported file in a spreadsheet program such as Excel or Google Sheets. Once you have the data in a spreadsheet use the Average function to determine the average decibel value of your recordings. Make sure to only use the part with the constant white noise of your recording to calculate the average decibel value.

Image Credit: Ben Finio, Science Buddies / Science Buddies

Screenshot of the phyphox app shows data being cropped from a sound intensity graph. The photo on the left shows the original graph with markers selecting the artifacts at the beginning and end of the graph. The photo on the right shows a new sound intensity graph of the data that remained from the previous photo.

Figure 5. Example data before and after zooming into the relevant area of the graph.

5. Groups can return to their work stations to modify and retest their containers as many times as they would like within the time limit. Make sure every group is aware of the time limit, and knows they should have their final design ready for the class competition.
6. If necessary, remind students about the decibel scale during testing. They might wonder why they can't get the reading all the way down to 0. Remember that 0 dB is the threshold of human hearing, and breathing is 10 dB. A container that can get sound levels down below 30 dB would be impressive!

   If you run out of time in a single class period, save the class competition for the next day.

Class Competition (30 minutes)

After each group has finalized its design (or time has run out, whichever comes first), test each group's container one at a time. Make sure the rest of the class is quiet and sitting still during each test, as any loud noises will disrupt the data. Record the results on the board (for example, a table with team name and average decibel value).

Reflect (10 minutes)

How do you define which design worked "the best"?

Since the goal was to design a device that insulated the phone from sound as much as possible, the best design will have the lowest average decibel value.

Do the best-performing designs have anything in common? For example, shape or materials used? What about the worst designs? What does this tell you about whether sound waves were reflected, absorbed, or transmitted through the materials?

The answer to this question will depend on the results in your individual classroom. In general, designs that work the best will reflect sound waves away from the phone and/or absorb them. Designs that work poorly allowed sound waves to be transmitted to the phone.

Based on the entire classroom's results, how could they make improvements to future designs, or combine their designs to achieve an even better result?

Assess

Use this quiz to assess student learning after the activity; quiz is available in online and pdf formats:

• Online quiz, assignable in any LMS
• Quiz (pdf) and answer key (pdf)

Make Career Connections

Discussing or reading about these careers can help students make important connections between the in-class lesson and STEM job opportunities in the real world.

Industrial Health & Safety Engineer

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Career Profile

An industrial safety and health engineer could monitor noise levels in a loud environment (like a factory or an airport runway) and make sure employees wear appropriate protective equipment. Read more

Materials Scientist and Engineer

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Career Profile

A materials scientist or engineer could develop new lightweight sound insulating materials for use in building construction. No more loud music from your neighbors! Read more

Lesson Plan Variations

• Can you do this activity with a device that does not totally enclose the phone? Try to find the exact position of the microphone and build a device that only covers the microphone, not the entire phone. Can your students still decrease the decibel readings? There are obvious applications for this in real life—for example, ear protectors only cover your ears, not your entire head!
• Try using a tone generator to play tones at different frequencies. Do some insulating devices work better at certain frequencies than others?
• Try placing requirements on the students' devices like a maximum size or weight. You can also assign a "cost" to each of the materials and give each team a maximum "budget" to work with. Devise a scoring system that rewards not only a lower average decibel value, but also lower weight, size, or cost.