1. Begin the activity by ringing a small bell until the class gives you their attention.

Figure 3.2. A bell may be rung loudly or softly.

The bell serves as a vehicle to engage students’ interest in the activity.

2. Challenge the class to name different ways to make the bell sound louder.

Students may suggest

• ringing the bell more vigorously so the clapper hits the side with more force,
• ringing the bell closer to their ears,
• cupping their hands around their ears to better focus the bell’s sound waves into them,
• placing the ringing bell at the small end of a megaphone to better project the sound waves toward the class, and
• placing the bell in front of a microphone that’s wired to an amplification system.

3. Explain that students will investigate the physical basis of loudness. However, before they can investigate loudness, they need to understand how scientists measure it. Distribute 1 copy of Master 3.1, The Decibel Scale, and Master 3.2, Sound-Intensity Table, to each student.
4. Explain that Master 3.2 contains a partially filled-out table that lists increasing sound levels (measured in decibels) with a description of a reference sound at some levels. Instruct students to complete the missing entries in the first two columns of the table.

If students have trouble understanding the relationship between sound intensity and decibels, use the first few entries on Master 3.2 as examples to clarify the relationship. Completing the worksheet will help students better understand the decibel scale and also reinforce the meaning of sound intensity and the large range of sound intensities that the human ear can detect. Only a few reference sounds are presented here. Students will have the opportunity to relate more sounds to the decibel scale during Lesson 5, Too Loud, Too Close, Too Long.

5. Show the class the overhead transparency of Master 3.2 and ask them how they filled in the first two columns of the table.

Students should respond that the sound levels increase by powers of 10. Furthermore, the number of decibels (dB) corresponds to the number of zeros in the sound-intensity column, followed by a zero. That is, a sound intensity of 1,000 in the table has a decibel value of 3 (as in 3 zeros) followed by a zero, or 30 dB.

6. To assess students’ understanding of the decibel scale, instruct them to answer the questions on Master 3.1, The Decibel Scale.

Answers to questions on Master 3.1, The Decibel Scale, follow:

Content Standard A:
Use mathematics in all aspects of scientific inquiry.

Question 1. How many times more intense is a sound of 30 dB than a sound of 20 dB? A sound of 40 dB than a sound of 20 dB?

A sound of 30 dB is 10 times more intense than a sound of 20 dB. A sound of 40 dB is 100 times more intense than a sound of 20 dB.

Question 2. How many times more intense is the sound of an alarm clock than a quiet room?

The sound of an alarm clock is 10,000 times more intense than a quiet room.

7. Ask the class why a sound will seem “too loud” to one person but not to another person.

People have different preferences for sound intensities. For example, some people prefer to listen to music at higher intensities than others. Differences in loudness perception can also result from damage to the hearing pathway. A person with a partial hearing loss will hear a given sound as less intense compared to a person with normal hearing. People who prefer to listen to loud music put themselves at risk for noise-induced hearing loss.

8. Ask the class how sound intensity is used in speech to communicate with others.

Sound intensity plays an important role in human speech. First, speaking loudly can convey an emotional state such as urgency or anger. Second, as seen in Lesson 2, putting greater stress (sound intensity) on a particular word can change the meaning of a sentence. Third, stressing a different syllable within a word can sometimes change its meaning.

1. Ring the small bell again until the class gives you their attention. Challenge the students to name as many ways as possible of making the bell sound higher in pitch.

Although they may not be able to explain the physical basis for the bell’s pitch, most students will probably know that its pitch is related to its size, and that the only way to increase the bell’s pitch would be to change (decrease) its size or somehow to electronically change the sound waves that it produces.

2. Explain to the class that they are now ready to study the relationship between loudness and pitch. Challenge students to explain the difference between these two properties of sound and to provide some practical illustrations of this difference.

Students should understand already that loudness is described using words such as loud and soft, whereas pitch is described by words such as high and low. Students should be able to explain that both the low-pitched keys on the left of a piano keyboard and the high-pitched keys on the right can be played softly or loudly. Similarly, males (with lower-pitched voices) can sing as loudly or as softly as females (with higher-pitched voices).

3. Ask the class to recall that sound travels as vibration. Explain that the physical basis of a sound’s pitch is its frequency, or the number of vibrations per second.

Sounds of rapid vibrations are perceived as higher in pitch than sounds of slower vibrations. The unit hertz (abbreviated Hz) is used to measure the pitch (frequency) of sound. For example, a sound with a pitch of 262 Hz vibrates at a rate of 262 times per second, which corresponds to middle C on a piano.

4. Explain to the class that they will use a Web-based activity to investigate the relationship between loudness and pitch and to understand the human hearing response to sound.
5. Have students proceed to http://science.education.nih.gov/supplements/hearing/student and click on “Lesson 3—Do You Hear What I Hear?” After listening to the introduction, you will advance automatically to a page containing a large graph, the loudness-pitch square.

Students should pay close attention to the introduction. It explains how changes in wave amplitude reflect soft versus loud sounds, and how changes in frequency reflect low- versus high-pitched sounds.

Figure 3.4. The loudness-pitch square.

Content Standard A:
Use appropriate tools and techniques to gather, analyze, and interpret data.

6. Explain to the class that they will perform two tasks using a loudness-pitch square. First, they will investigate the relative loudness of sounds at different pitches. Then, in Part 2, they will construct a hearing-response curve.

Students may work in teams, although each student should collect his or her own data.

7. Distribute to each student a copy of Master 3.3, Loudness and Pitch.
8. In the first task, students select the lowest frequency (62.5 Hz) and click on a point halfway up the y-axis (50 on the loudness axis).

Depending on your computer, sound card, and speakers, you may not be able to hear the lowest or highest frequencies, even at the maximum intensity. Also, students might hear a very short “squeak” initially. Tell them to ignore this noise and listen for a constant, uniform tone.

9. For the first constant, uniform tone that students hear at 50 on the loudness axis, tell them to assign that tone a value of 1 (on a scale of 1 to 10).

Other tones may be louder than this one, and they will be assigned an arbitrary number relative to 1.

10. Students should then select the next higher frequency on the graph, clicking on the point at the same vertical height as before (50 on the loudness axis). Instruct students to assign the tone a numerical value based on its loudness relative to the first detectable tone (see Step 9). For example, if you think the second tone is twice as loud as the first, then you should assign the second tone a value of 2. This process is repeated for each of the remaining frequencies, always clicking on the same point on the loudness axis (at 50) for each frequency. Students should then enter their results on Master 3.3, Loudness and Pitch.
11. Instruct the students to answer the discussion questions on Master 3.3, Loudness and Pitch.

Question 1. Did the sounds produced at each frequency seem equally loud? How did the loudness change with frequency?

Sounds vary in loudness as pitch (frequency) increases. At the low end of the spectrum, the sounds seem louder as frequency increases. As one moves up the spectrum, however, loudness seems to decrease at the higher frequencies.

Question 2. Why did you hear variation in loudness with changing pitch?

The hearing system’s sensitivity to loudness varies with the frequency of the sound. Generally, the ear is most sensitive to sounds in the 3-to-4-kHz region. Sounds outside of this range must be more intense to be perceived as loud. Any student answer that relates this phenomenon to the functioning of the human hearing system is acceptable.

1. Give each student a copy of Master 3.4, Hearing Response.
2. Instruct students to start with the 62.5-Hz frequency and play the tone at the lowest setting for loudness. If they do not hear the tone, they should increase the loudness by clicking on a higher point on the vertical axis at that same frequency. They should continue this process until they find the loudness setting at which they can first hear the tone. Direct students to enter this loudness value in the appropriate space on Master 3.4, Hearing Response.

Note: the lowest frequency the students hear may be at 250 Hz, 125 Hz, or 62.5 Hz depending on the quality of the computer’s sound card and speaker system.

Content Standard A:
Use mathematics in all aspects of scientific inquiry.

3. Students repeat this process for each of the higher frequencies by clicking on the lowest loudness setting and gradually increasing the volume. As before, they should record the loudness at which they first hear the tone. In the end, students will collect data representing the minimum relative loudness at which tones of various frequencies first can be heard.

Note: that at the two highest frequencies, students might hear a very short “squeak” initially. Instruct them to ignore this noise and listen for the loudness setting at which they hear a constant, high-pitched tone.

4. Direct students to plot their results on the graph template provided on Master 3.4, Hearing Response. You can use an overhead transparency of Master 3.4 to explain how to create the graph.

Student results will vary, although the shapes of their curves should be similar. The values on the y-axis are high at the lowest frequencies, drop for frequencies from 500 to 4,000 Hz, and slowly rise beginning around 8,000 Hz.

Figure 3.5. A sample hearing-response curve.

5. Instruct the students to answer the discussion questions on Master 3.4, Hearing Response.

Answers to questions on Master 3.4, Hearing Response, follow:

Question 1. At what frequencies is your hearing most sensitive? Circle these frequencies on your graph.

Hearing is most sensitive at those frequencies for which sound can be detected at the lowest loudness levels. Human hearing is most sensitive at frequencies associated with human speech (between 250 and 4,000 Hz).

Question 2. As we get older or are repeatedly exposed to loud sounds, we tend to lose hearing at higher frequencies. How might the hearing-response curve change for an individual with high-pitched hearing loss?

As hearing loss occurs, progressively louder sounds are required for higher-pitched sounds to be heard. The hearing-response curve for a person with high-pitched hearing loss would show a steeper curve on the part of the graph corresponding to high frequencies. Because louder sounds cause damage to hair cells, a mild hearing loss can lead to even greater hearing loss.

1. Explain to the class that they are now ready to investigate the effect of high-pitched hearing loss on the understanding of sounds. Challenge students to predict how speech would sound if the high pitches are removed, or “filtered,” from a sound file.
2. Explain that, as in the first lesson, students will again listen to someone reading the first sentence of President Lincoln’s Gettysburg Address. Explain that the first reading will be an unfiltered version. (This is the same track used in Lesson 1 and labeled “traditional.”) The second reading has removed pitches above 4,000 Hz. The third reading has removed pitches above 2,000 Hz. Instruct students not to change sound level settings while listening to the three recordings.
3. Have students proceed to http://science.education.nih.gov/supplements/hearing/student and click on “Lesson 3—Do You Hear What I Hear?” Near the top of the screen, click on the link labeled “Filtered Sound.” Have students play each of the three sound tracks in the following order: normal; filtered 4,000 Hz; and filtered 2,000 Hz.
4. After the students have had an opportunity to listen to the unfiltered and filtered sound tracks, reconvene the class and ask the students the following questions:

1. Which sound track might simulate how an older person with high-pitched hearing loss would hear the passage?

Both the filtered 4,000-Hz and the filtered 2,000-Hz sound tracks simulate how a person with high-pitched hearing loss might hear the passage being read. The filtered 2,000-Hz sound track corresponds to a more severe hearing loss than does the filtered 4,000-Hz sound track.

2. Which sound track, filtered 4,000-Hz or filtered 2,000-Hz, is missing more pitches?

Pitches ranging from 2,000 Hz and above have been removed from the filtered 2,000-Hz sound track, while pitches ranging from 4,000 Hz and above have been removed from the filtered 4,000-Hz sound track. Therefore, the filtered 2,000-Hz sound track is missing pitches between 2,000 Hz and 4,000 Hz, which are present in the filtered 4,000-Hz sound track.

3. How does loudness change as the higher pitches are removed?

Loudness seems to decrease as pitches are removed.

Assessment:
Have students investigate the hearing responses of another animal such as a dog, bat, or whale. Ask them to report on their animal’s hearing range and compare it with that of humans. Ask them to predict how high-pitched hearing loss might affect the animal.

4. How does your understanding of the words change as the higher pitches are removed?

Understanding becomes more difficult. Words seem to be less distinct. This is because some of the information provided by the sound has been lost.

5. How can a person compensate for such a hearing loss? What is the result of this compensation?

As hearing loss occurs, progressively louder sounds are required for hearing. An individual may turn up the volume on a television, stereo, or radio or ask a speaker to talk louder. Students may have noticed such behaviors exhibited by their grandparents or other older adults. A person with such a hearing loss may elect to use a hearing aid, which uses a microphone to collect and amplify sounds coming into the ear. The hearing aid does not restore normal hearing but can greatly aid hearing and communication.