Classroom Noise Meter

Background Information for Teachers

What is sound? In technical terms, sound is the movement of air in the form of a pressure wave. This movement of air is usually caused by a vibrating object. For example, this is how musical instruments create their sound. A drummer hist a drum to make its membrane vibrate; an oboe player blows into a reed, causing it to vibrate; and a guitar player plucks a string to make it vibrate. Humans can also generate sounds with their voice. Although you cannot see the vibrations that cause your voice's sound, you can feel them when you put your hand on your throat while humming or talking. This is where your voice box, also called larynx, is located. Within the voice box we have our vocal folds, also called vocal cords, as shown in Figure 1.

Image Credit: Wikimedia commons user CRUK / Public Domain
Figure 1. Cross-sectional view of a human head and throat that shows the location of our voice folds (voice cords) in our voice box.

These vocal folds are key for creating sound with our voice. The vocal folds are two bands of elastic muscle tissue stretched horizontally, from back to front, across the voice box as seen in Figure 2 on the left. They are located side by side just above the windpipe (trachea). The vocal folds are able to close and open our windpipe by vibrating back and forth as shown in Figure 2 on the right. When we are not speaking or inhaling, our vocal cords are open, so the air we breathe in can make it into our windpipe. When we speak, they start to vibrate and thus create a sound. But why do they start vibrating?

Image CreditImage Credit: Wikimedia Commons / Public Domain
Figure 2. Top view (left) and cross-sectional view (right) of the vocal folds (vocal cords) opening and closing.

The vibrations are caused by the air we breathe. Our breath is basically the fuel for our voice. When exhaling, air is pushed from our lungs through the narrow opening between the vocal folds. The force of this air causes the vocal folds to vibrate. As the vocal folds open and close, the air flow will be alternately interrupted and allowed to pass. This results in a fluctuation in air pressure that produces a sound wave. A sound wave consists of a repeating pattern of high-pressure and low-pressure regions in the air, as shown in Figure 3, traveling through the air in the form of a pressure wave. You can illustrate the low-pressure (rarefaction) and high-pressure (compression) zones of a sound wave in a graph showing pressure versus distance or time. The sound wave in Figure 3 shows how the pressure at a single point in time changes over a distance.

Image Credit: Svenja Lohner, Science Buddies / Science Buddies
Figure 3. The vibrations of the vocal folds create sound waves. The sound wave can be represented with dots showing air particles. The dots are closer together in the high-pressure zones (compressions) and farther apart in low-pressure zones (rarefactions). The sound wave can also be represented using a graph with pressure on the y-axis and distance on the x-axis, where a positive y-axis value corresponds to higher pressure (compression) and a negative y-axis value corresponds to lower pressure (rarefaction). Both methods represent the sound wave at a single snapshot in time.

When the sound waves reach our eardrums, they cause the bones in our middle ear to vibrate, and the vibrations are transmitted to fluid in our inner ear. Then, the vibrations travel to the inner ear hair cells and to the nerves that carry the signal to our brains where we interpret the signal as sound.

Image Credit: Svenja Lohner, Science Buddies / Science Buddies

When sound waves enter a human ear they travel past the outer ear until they hit the ear drum. The ear drum vibrates air trapped in the inner ear and a nerve sends a signal to the brain which can decipher the vibrations as different sounds.

Figure 4. Our ear translates sound waves into a sound that we can hear.

This explains how we can make sounds with our voice and how we can hear sounds, but it does not explain why there are so many different sounds with various pitches and volumes. To answer this question, we have examine the properties of a sound wave in more detail. In addition to speed, you can describe waves by their frequency, period, and amplitude (Figure 5). Let's start with frequency (f). The frequency of a wave describes how many cycles of the wave occur per unit of time. This is dependent on how fast the object that creates the sound wave (such as the vocal folds) are vibrating. Frequency is measured in Hertz (Hz), which is the number of cycles per second. Figure 5 (on the left) illustrates examples of sound waves of two different frequencies. Note that the graphs in this figure show time on the x-axis, not distance as in Figure 3. These graphs show how the pressure at a single point in space (a fixed distance) changes over time. The frequency of a sound wave determines the pitch of a sound. The higher the frequency, the higher the perceived pitch. On average, the frequency range for human hearing is from 20 Hz at the low end to 20,000 Hz at the high end. Figure 5 also shows the period (T) of the wave, which is the time it takes for one complete wave to pass a given point. The period is simply the reciprocal of the frequency (T = 1/f).

Image Credit: Svenja Lohner, Science Buddies / Science Buddies

Diagrams showing the impact of sound wave frequency and amplitude on pitch and volume of sound. The diagram on the left shows the impact of frequency on pitch-- as low frequency waves produce lower pitch sounds, while high frequency waves produce higher pitch sounds. The diagram on the right shows the impact of amplitude on volume-- as lower amplitude waves produce quieter sounds while higher amplitude waves produce louder sounds.

Figure 5. Illustration of sound waves with different frequencies and amplitudes, representing sound waves of different pitches and volumes respectively.

Finally, the amplitude of a wave is the distance from the center line to the top of the peak or the bottom of the trough, which for a sound wave is measured in units of pressure. For a sound wave, the amplitude is connected to the loudness of the sound you hear. Figure 5 (on the right) shows examples of waves with two different amplitudes. The higher the amplitude, the louder the sound. The intensity of sound is measured in decibels (dB). Figure 6 shows the decibel ratings of some common sounds. Decibels are a logarithmic scale, not a linear scale. This means that for every increase of 10 dB, the sound intensity increases by a factor of 10. For example, sound with an intensity of 40 dB is 100 times as intense as 20 dB, not twice as intense. However, while we may use the terms interchangeably in everyday speech, loudness and intensity are not the same thing (see this article from Georgia State University for a more detailed explanation). Most of us perceive a sound to be "twice as loud" as another one when they are about 10 dB apart. 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 showing the decibal levels of common sounds with 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 6. Decibel levels of some common sounds. Remember that the decibel scale is nonlinear. Every increase of 10 dB corresponds to roughly doubling the perceived loudness of the sound. So, for example, a chainsaw (100 dB) does not sound twice as loud as moderate rainfall (50 dB); it sounds 32 times as loud!

In this lesson plan, your students will determine the appropriate sound levels for different classroom scenarios such as working in groups, working independently, or listening to the teacher. To do this, they will investigate how the sounds they make with their voices translate into different sound intensities. To be able to measure different sound levels, students will use their mobile phones and a specific sensor app, which uses the microphones built into smartphones to measure sound. The app helps your students to record and visualize the intensity of the sounds they create with their voices, allowing them to discover the relationship between the properties of the sound waves and what they hear.

Additional Background Links

• Properties of Waves, Ducksters.com
• Standing Waves, The Physics Hypertextbook
• Physics of Sound, the Method Behind The Music
• Fundamental Frequency and Harmonics, The Physics Classroom
• Loudness, HyperPhysics
• Ruben's Tube - waves of fire, The Naked Scientist
• How your voice works, The Washington Post
• Your Changing Voice, KidsHealth
• Low-Level Classroom Noise Distracts, Experts Say, Education Week

Prep Work (30 minutes)

• Do your own research on average classroom noise levels. Some initial articles are listed below. Ideally, you have some target decibel levels in mind for each of the working scenarios before you start the lesson. This way you can direct your students into the desired range during their investigations.
• Print out a student worksheet for each student.
• 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.

https://www.youtube.com/watch?v=3cpZEVSC6Nw

Create Assignment

Embed Link

Google Classroom

Microsoft Teams

Canvas

Schoology

Other

Link copied to clipboard.

Engage (40 minutes)

1. Start the lesson by showing this video to your students. Have students take notes about what they hear and learn in their student worksheet.
   

   https://www.youtube.com/watch?v=1ZcOusmB4Ls
2. Ask questions about the video:

   What did the experiment they set up in this video look like?

   Based on your student's answers, make a schematic drawing of the Ruben's tube (Figure 7) for everybody to see that illustrates how the experiment works. Image Credit: Svenja Lohner, Science Buddies / Science Buddies Figure 7. Experimental setup of the Ruben's tube. The video shows a demonstration of the Ruben's Tube. It consists of a long tube in which small holes are drilled at regular intervals. Both ends of the tube are sealed. On one end a gas line is inserted into the tube, which fills the tube with flammable gas. On the other end of the tube a loudspeaker or frequency generator is placed that produces sounds. When the gas is lit up, small flames will be coming out of the drilled holes. When a sound is generated with the loudspeaker, the sound wave travels to the end of the tube and, as the tube is sealed, will be reflected back. At certain frequencies two traveling sound waves (back and forth) can combine to form a standing wave, which appears to be static in space. Depending on the local pressure inside the tube caused by the sound wave, the gas inside the tube will be pushed out more or less strongly, which causes some flames to stand higher than others. This results in the flames representing the shape of the standing where the areas of higher and lower flames match the areas of higher and lower pressure created by the sound waves in the tube. You can even determine the frequency of the sound wave by measuring from the flame minimum and maximum with a ruler.

   What did you learn about sound in this video?

   Collect answers from students and write them on the board for everyone to see. Some examples the video talked about are listed below. Sound is a wave. We create sound waves with our vocal cords when they vibrate. The sound wave consists of areas of low pressure and high pressure in air. The sound wave travels through the air. A higher sound pitch means the peaks of a sound wave are closer together. A higher pitch means changing the wave's frequency to a shorter wavelength. A shorter wavelength (or higher frequency) means a faster vibration of the object making the sound. If your students have a hard time answering this question, here are some prompting questions that might help initiate a discussion. Why do the flames look like a wave? Why does the shape of the flames change? What is a sound wave and how is it generated? What happened to the flames when Dr. Phil changed the pitch of the sound? Can you explain why this happened? What is different between a sound wave with a lower and a higher pitch?

3. Using the answers from your students, define what a sound wave is for class. Then ask your students to draw a sound wave in the graph template provided in their worksheets. Review the characteristics of a sound wave (frequency) together and let your students draw sound waves with a low frequency and a high frequency.
4. Continue the discussion about the video.

   You probably noticed that the shape of the flames also changed when Dr. Phil used the microphone and his voice instead of a loudspeaker. How can we make a sound with our voice?

   Dr. Phil states in the video that we create sound waves with our vocal cords that vibrate.

5. Ask students to put one hand on their throat while humming or talking.

   What do you notice?

   Students should feel their throat vibrating. Point out that this is due to our vocal cords located in our voice box, which is inside our throat, that start vibrating when we talk, sing, hum, or make other sounds. These vibrations create a sound wave (pressure wave) that is traveling through the air so our ears can pick them up and hear them.

6. Point out that besides the vocal fold several other parts in our head and throat are important for our ability to talk. Refer students to the image in their worksheet that shows the cross section of a human head and have them label the parts with arrows (Figure 8). Then have them speculate what the function of each part is.
   
   
   Image Credit: Svenja Lohner, Science Buddies / Science Buddies
   Figure 8. Cross section of human head showing parts that are important for our ability to talk.
   
   

   What kind of sounds can we make with our voice?

   Collect answers from students. Elicit answers that mention that we can make high pitch sounds and low pitch sounds, or that we can speak quietly or very loudly. Have students try doing different kind of sounds with their voices.

   How does a sound wave change if the sound gets louder versus quieter?

7. Draw two sound waves on the board. One with a high amplitude and one with a low amplitude (see Figure 5 in the teacher background).

   Which of these sound waves do you think represent a loud sound versus a quiet sound?

   What is the difference between these two graphs?

   Point out that the sound wave with the higher amplitude represents the loud sound and the sound wave with the low amplitude represents the quiet sound.

8. Have students draw a sound wave with high and low amplitude in the graph templates provided in their worksheets. Then explain that the distance from the center line to the top of the peak or the bottom of the trough is called the amplitude. The amplitude of a sound wave indicates the sound intensity, or the loudness of a sound.

   How do we know how loud or quiet a sound is? Is there any way for us to measure the intensity or loudness of a sound?

   Tell your student that there are devices that can measure the frequency and amplitude of a sound wave, meaning they determine the pitch and loudness of a sound. Sound intensity is measured in decibels (dB). Explain that if the number of decibels doubles, the loudness more than doubles because it is measured on a logarithmic scale. For example, a chainsaw (100 dB) is much more than twice as loud as moderate rainfall (50 dB). In this lesson, they will use such a device to measure the sound levels of their voice.

Explore (50 minutes)

1. Explain to your students that they will use a special sensor app that allows them to use the microphone in their mobile devices to measure the sounds around them. 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 re-calibrate their sensor every time they start a new recording!

   Divide your class in groups of 4 students. Each group can share a mobile device.

2. Give students some time to explore how the sound sensor works.
   1. First, they need to locate the microphone in their mobile device.
   2. Then have them open the audio amplitude function in the phyphox app.
   3. Tell students to check if their sensor is calibrated or to re-calibrate their sensor before each recording.
   4. Let them press the play button and watch how the graph fluctuates as they talk or make noise.
   5. Have them take some recordings and emphasize that they should save their data after each recording.
   6. Remind them to keep their microphone (sound sensor) at the same location throughout their entire investigation. A good place would be on their table, so it is equally accessible to everyone.
3. State the challenge to your students. Their task is to measure the noise levels in their classroom for different working scenarios. Describe the five scenarios to your students.
   
   

   Scenario 1: Background noise	Everybody is trying to be as quiet as possible (students and teacher).
   Scenario 2: One speaker	One speaker (teacher) talks and all students are quiet and listen.
   Scenario 3: Independent work	Students are given individual work that they have to complete on their own.
   Scenario 4: Discussion in pairs	Students are given an exercise that they have to complete as a pair. Only two students can talk quietly with each other.
   Scenario 5: Group discussion	Student get a group assignment. All students can talk to each other but should not talk over each other.

   
   
4. Students have to act out each of these scenarios and record the sound intensities of their surroundings along the way. Their goal is to measure and determine the optimal sound levels for each working scenario.
5. Guide your students through the five different scenarios. Each scenario (except the first one) should last for about five minutes, so students have enough time to gather their data. Instruct them to take recordings of the sound intensity of the sounds in their environment for each scenario.
   1. They should take one continuous recording for the whole scenario and save it afterwards.
   2. For each scenario they need to make sure that the sound sensor/microphone is located at the same position as for the previous scenario and that their sensor is calibrated correctly.
   3. If something happens that affects their data during one of their recordings (such as somebody sneezing, coughing, or dropping something), have students make a note of it so they can label the event in their recording later.
6. Give a signal to your students that scenario 1 is starting, which means everybody should be as quiet as possible, so they can determine their classroom background noise level. Remind your students to check the calibration status of their sensor before they start recording their data. When students save their data have them label their recordings respectively. Try to stay quiet for at least 1-3 minutes.
7. Then interrupt the silence and tell your students it is time to move on to scenario 2, which means that they should be quiet and listen to you. Again, remind them to check the calibration status of their sensor, record their data and save and label their recordings. Then use the next 5 minutes to introduce your students to the sound levels of common sounds (see Figure 6 in the teacher background section), so they have a reference point for their data. Talk about the decibel scale being a logarithmic scale and how different sound levels can be compared. Also point out, at which decibel level sound becomes harmful to your ears.
8. Once you are done, tell students to stop taking data and move on to scenario 3. Assign a lesson-related reading material to each student to quietly read by themselves. One suggestion is given below. Again, remind your students that they should not forget their sound level measurements for this scenario. They will also need to re-set the calibration offset for the sensor before they start their recording. If students get too loud, intervene and direct students to your desired sound level for this scenario.
   • Your Changing Voice
9. After about 5 minutes, ask students to wrap up their reading and continue with scenario 4. Tell students they should discuss, in pairs, what they have learned from their reading. They can alternate which two students in a group talk to each other, but it can only be two students talking to each other at a time. Remind them again to take a recording of their sound levels. Again, they will need to re-set the calibration offset for the sensor before they start recording. If students get too loud, intervene and direct them to the desired sound level.
10. Finally, after 5 minutes, all four students within one group can talk to each other. Ask them to discuss what their favorite music is and why they like the sound of this music. Remind them to not talk over each other. Have them measure and record the sound intensities throughout their group discussion as well. They will need to re-set the calibration offset for the sensor before they start their recording.
11. After another 5 minutes, conclude this part of the investigation and tell your students that it is now time to analyze their measured data.
12. For data analysis, have students review each of their recordings within the sensor app. They will also need to export their data from the app and can do that either as a .csv or Excel file. Students can then open the exported file in a spreadsheet program such as Excel or Google Sheets. Once they have their data in a spreadsheet they can use the Minimum, Maximum, and Average functions to determine the minimum, maximum, and average sound intensities measured for each scenario and fill out the data table in their worksheets (Table 1).

Reflect (40 minutes)

1. Once students have reviewed their data, let them discuss the following questions within their groups.

   What is your classroom background noise level? Where do the background noises come from if nobody is talking?

   How do your average/maximum/minimum sound levels compare for each scenario?

   Do you see a pattern, or a trend in your data when comparing sound levels for each scenario?

   Do you have any outliers in your data, meaning some sound readings that do not seem to fit with the rest of your data within a scenario? For example, one or more extremely high noise events as represented by a large peak on your graph? How many outliers do you have?

   What was your highest measurement throughout the whole investigation? What event caused that level of noise?

2. Continue the discussion with the whole class. Let each group briefly share their observations and ask them what their average sound intensity measurements were for each scenario. Write these numbers in a data table (Table 2) on the whiteboard for everyone to see. Then discuss:
   
   
   Swipe left to see more

   Average sound intensities [dB]	Scenario 1: Background noise	Scenario 2: One speaker	Scenario 3: Independent work	Scenario 4: Discussion in pairs	Scenario 5: Group discussion
   Group 1
   Group 2
   Group ...
   Average of all Groups

   Table 2. Data table to collect measured data from each group.

   Are the average sound intensities measured by each group very different or similar? What could be the reason for significant differences?

   If all groups followed the instructions properly, the average sound levels should be in a similar range. Exceptions are possible if there were multiple high sound intensity events in one group (such as sneezing, something falling on the floor, etc.) that skewed their measurements.

3. As a class, calculate the average sound intensity for all groups for each scenario. Have your students document these numbers in their worksheets.
4. Then ask students to draw a bar graph presenting their final results in the graph templated provided in their worksheets.
5. Review these final numbers in their graph as a class and discuss:

   Do you see a trend in this data?

   Based on what you have learned about different sound levels during this lesson, do you think these are reasonable sound levels for each classroom scenario? Explain your reasoning.

6. Based on your data and discussion, determine the "target sound levels" for each working scenario as a class. Tell your students that the sound levels they just determined for each working scenario are what they are committing to for the rest of the school year.
7. Conclude the lesson by creating a "noise meter" poster for the classroom that indicates their determined "target sound levels" for each working scenario. Let students be creative in decorating the poster and hang it up in the classroom for everyone to see.

Assess

You can use this quiz to assess student learning after the activity:

• 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.

Audiologist

Add Favorite Remove Favorite More Menu

• Read More

Career Profile

Audiologists help people with hearing disorders that have difficulties hearing sounds. Using special equipment, they perform tests to measure the sound intensity at which a person begins to hear sounds and to measure a person's ability to distinguish sounds with different frequencies. They use their test results to make a diagnosis and determine the right treatment to improve hearing problems. Read more

Physicist

Add Favorite Remove Favorite More Menu

• Read More

Career Profile

Physicists study a wide range of physical phenomena such as electricity, magnetism, or sounds. The branch of physics that studies sounds is called acoustics. Acousticians, or acoustical engineers, explore how sounds can be produced or controlled, and help manage the noise levels in homes, workplaces or the environment, for example by designing sound insulation systems. Read more

Lesson Plan Variations

• Have your students take their mobile phones and the sensor app to different areas within the school. How do the sound levels at different locations compare? Which is the loudest place in school, which one the quietest?
• In addition to measuring how loud their voices are for different scenarios, let your students explore the frequency range of their voices. How high or low can they go? To do this, you can use the frequency history function within the phyphox app.
• Challenge students to measure the noise levels in their homes. How loud do they listen to their TVs, what are the sound levels during dinner, etc.? Have students gather data for different everyday situations at home over a certain period of time. Then collect the data as a class and discuss the results.