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Classroom Noise Meter

Summary

Grade Range
6th-8th
Group Size
4 students
Active Time
2 hours 10 minutes
Total Time
2 hours 10 minutes
Area of Science
Physics
Key Concepts
Sound waves, frequency, pitch, amplitude, sound intensity
Credits
Jill Magruder, M.Ed.
Svenja Lohner, PhD, Science Buddies
Drawing of a speaker next to bars representing sound levels

Overview

Do you feel like it is always too loud in your classroom? In this lesson you can find out exactly how loud it is. Using a mobile phone and a sensor app, your students will measure and graph the sound levels in your classroom for different working scenarios. How loud are your students when doing independent work, having a group discussion, or listening to their teacher? Based on your students' data, you will determine as a class which sound levels are ideal for each scenario and create a classroom poster that reminds your students of these sound levels throughout the school year.

Learning Objectives

NGSS Alignment

This lesson helps students prepare for these Next Generation Science Standards Performance Expectations:
This lesson focuses on these aspects of NGSS Three Dimensional Learning:

Science & Engineering Practices
Planning and Carrying Out Investigations. Collect data to produce data to serve as the basis for evidence to answer scientific questions or test design solutions under a range of conditions.

Conduct an investigation and/or evaluate and/or revise the experimental design to produce data to serve as the basis for evidence that meet the goals of the investigation

Analyzing and Interpreting Data. Analyze and interpret data to provide evidence for phenomena.
Disciplinary Core Ideas
PS4.A: Wave Properties. A simple wave has a repeating pattern with a specific wavelength, frequency, and amplitude.
Crosscutting Concepts
Patterns. Graphs and charts can be used to identify patterns in data.

Cause and Effect: Mechanism and Prediction. Cause and effect relationships may be used to predict phenomena in natural or designed systems.

Materials

Materials per group of 4 students:

Background Information for Teachers

This section contains a quick review for teachers of the science and concepts covered in this lesson.

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.

Drawing of a neck shows the vocal chords behind the Adam's apple in the center of the voice boxImage 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?

Drawing of vocal folds open above vocal folds which are closedImage Credit Drawn animation of vocal foldsImage 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.

Sound from opening and closing vocal folds is represented by both a transverse and longitudinal waveImage 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.

Diagram of sound waves from a dogs bark interacting with the inner mechanisms of the human earImage 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).

Diagram of the frequency and amplitude of wavelengthsImage 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.

Bar graph displays the decibel levels of common soundsImage 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.

Prep Work (30 minutes)

Engage (40 minutes)

Explore (50 minutes)

Reflect (40 minutes)

Assess

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