Students learn how loudness is measured. Using a Web-based loudness-pitch square, students generate a hearing-response curve. They also listen to recordings that simulate hearing loss. Students investigate the relationships among loudness, pitch, and hearing.
Loudness and pitch are distinct properties of sound. Loudness is related to the amplitude of the sound wave; pitch is related to its frequency. Humans do not hear all pitches equally well. Specifically, the loudness of very-low- and very-high-pitched sounds must be increased to detect them. A healthy sense of hearing is characterized by an ability to recognize a wide spectrum of pitches. Hearing loss may involve failure to detect specific pitches.
After completing this lesson, students will
Consult the following sections in Information about Hearing, Communication, and Understanding:
|Activity 1|| Master 3.1, The Decibel Scale (Make 1 copy per student.)
Master 3.2, Sound Intensity Table (Make 1 copy per student and prepare an overhead transparency.)
|Activity 2|| Master 3.3, Loudness and Pitch (Make 1 copy per student.)
Master 3.4, Hearing Response (Make 1 copy per student and prepare an overhead transparency.)
|Activity 1||a small bell|
|Activity 2||a computer with an Internet connection and a sound card|
To achieve the best results, calibrate the computer sound levels with the Web activity. To do this, go to http://science.education.nih.gov/supplements/hearing/web click on “Web Portion of Student Activities.” Then 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. Play the 2,000-Hz (2-kHz) tone at a value of about 20 on the loudness scale (y-axis). Adjust the volume control on the speakers so that the tone is barely audible. This will ensure that your computer plays the tones at appropriate volumes for the activity.
This activity is concerned with measuring levels of sound intensity. Sound intensity is a scientific measurement representing power per unit of area and is expressed as watts per meter squared (W/m2). Loudness, on the other hand, is a subjective impression of sound intensity. Perception of loudness varies from person to person. It is influenced by factors such as sound frequency (we don’t hear all frequencies equally well) and the performance of our hearing (a person with a partial hearing loss may perceive a given sound as being less loud than a person with normal hearing does). Although sounds of greater intensity are louder than sounds of lesser intensity, use of the term loudness does not permit us to make quantitative comparisons. Therefore, in this activity, we will focus on measuring and comparing sound intensity rather than loudness.
The bell serves as a vehicle to engage students’ interest in the activity.
Students may suggest
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.
|Sound Intensity||Decibels (dB)||Sounds|
|100,000,000,000||110||rock concert (90–130 dB)|
|1,000,000,000,000||120||shout into ear at 20 cm|
|100,000,000,000,000||140||air raid siren|
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.
Answers to questions on Master 3.1, The Decibel Scale, follow:
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.
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.
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.
Figure 3.3. Speech can be either loud or soft.
In this activity, students generate a hearing-response curve, which depicts the threshold of hearing as a function of frequency. This technique is the basis for a test commonly used to detect hearing loss. However, this activity should not be used as a diagnostic tool in any way. Students will likely generate curves that differ from each other. These differences are much more likely to be caused by differences between computers than differences between students’ hearing.
PART 1—LOUDNESS AND 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.
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).
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.
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.
Students may work in teams, although each student should collect his or her own data.
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.
Other tones may be louder than this one, and they will be assigned an arbitrary number relative to 1.
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.
PART 2—HEARING-RESPONSE CURVE
In this second task, students generate a hearing-response curve. This curve has no clinical value and should not be viewed by students as an indication of whether or not they have a hearing impairment. However, if a student has responses that are well outside the norm and is concerned, encourage him or her to see the school nurse, a doctor, or an audiologist. The purpose of this task is to explore the different sensitivities of the human ear to different pitches. If you or the students have not already calibrated the sound level of their computer as described in the Preparation section at the beginning of this activity, instruct them to do so now.
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.
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.
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.
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.
PART 3—HIGH-PITCHED HEARING LOSS
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.
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.
Loudness seems to decrease as 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.
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.
|Activity 1: Measuring Intensity|
|What the Teacher Does||Procedure Reference|
Ring a small bell and challenge the class to suggest ways of making the bell ring louder.
Steps 1 and 2
Introduce the concept of the physical basis of loudness and the decibel scale using Masters 3.1, The Decibel Scale, and Master 3.2, Sound-Intensity Table.
Have the class complete Master 3.2, Sound-Intensity Table, and discuss their answers.
|Steps 4 and 5|
Instruct the class to answer the questions on Master 3.1, The Decibel Scale.
Discuss the relationship of loudness to human communication.
|Steps 7 and 8|
|Activity 2: Pitch Me a Curve|
|What the Teacher Does||Procedure Reference|
|Ring the small bell again and challenge the class to suggest ways of making the bell sound at a higher pitch.||Part 1, Step 1|
Ask the class to distinguish between loudness and pitch and relate their answers to the concept of sound waves.
|Part 1, Steps 2 and 3|
Have students log onto the Web site and click on the button labeled “Lesson 3—Do You Hear What I Hear?”
|Part 1, Steps 4 and 5|
Have students collect data on the relative loudness of sounds using the loudness-pitch square and Master 3.3, Loudness and Pitch.
|Part 1, Step 6–10|
Have students answer questions on Master 3.3, Loudness and Pitch.
|Part 1, Step 11|
Have students collect data on a hearing-response curve using Master 3.4, Hearing Response.
|Part 2, Steps 1–3
Have students plot their data and answer the questions on Master 3.4, Hearing Response.
|Part 2, Steps 4 and 5|
Challenge students to describe how speech would sound with high pitches removed.
|Part 3, Step 1|
Have students return to the Web site and play unfiltered and filtered sound tracks.
|Part 3, Steps 2 and 3|
Reconvene the class and discuss the following questions:
|Part 3, Step 4|
|= Involves copying a master.|
|= Involves using a transparency.|
|= Involves using the Internet.|