Module 1

Module 1—The Nervous System

Module 1: Lesson 6 Assignment

 

Lab—Hearing: Pitch and Loudness

 

To apply your understanding of pitch and volume, open the Module 1: Lesson 6 Assignment that you saved to your computer earlier in this lesson. You will complete Part 1—Lab using the Frequency and Volume Gizmo. Read through the entire lab before beginning.

 

Have you ever blown a dog whistle? Could you hear it? Probably not, because the sound frequencies produced by a dog whistle are higher than the range of sounds humans can hear. You’ve probably observed animals that seemed to be agitated by sounds that you couldn’t hear. You may have heard an older person say “speak into my good ear.” The range of sounds that can be heard gets smaller as people age, especially if they are repeatedly exposed to loud sounds from lawnmowers, snowmobiles, heavy traffic, sirens, loud concerts, MP3 players, and televisions.

 

In this exercise you will test your hearing range by listening to low-, medium-, and high-frequency sounds. You will compare the relative loudness of sounds at each frequency to create an equal-loudness curve and a curve for your threshold of audibility.

 

Note: It is important for you to read the procedure for the lab beforehand so that you can choose your subjects and so that you can make an honest prediction as to how each of your subject’s results will compare with your own readings in terms of the sounds participants can detect.

 

Problem (Purpose)

 

What is your threshold of audibility for different frequencies, and how do your results compare to others?

 

Materials

 

No additional material are required other than access to the “Hearing: Frequency and Volume Gizmo.” Read the rest of the lab information before opening the gizmo.

 

You may be required to enter a username and password to access the gizmo. Contact your teacher for this information.

 

Prediction

 

If you are posting your equal loudness curve and your threshold of audibility curve, predict whether your classmates’ curves will be higher, lower, or the same as yours. Using what you have learned about the ear and hearing, explain why you think the curves will be as you have predicted.

 

OR

 

If you are using members of your family who are of different ages, predict whether their equal loudness and threshold of audibility curves will be higher, lower, or the same as yours. Using what you have learned about the ear and hearing, explain why you think the curves will be as you have predicted.

 

Procedure

 

Step 1: First, eliminate as much of the background noise where you are as possible. Background noise is the sounds coming from sources other than your computer’s speakers or headphones, such as a radio or a fan. Use headphones if you have access to them.

 

Be sure the system volume slider is set to 1 and click the “test” button. If the sound is too loud, turn down your system’s speakers or the computer’s volume and click “test” again. If the sound is too soft, turn up your speakers or adjust the system volume slider until a comfortable volume is reached.

 

Step 2: The pitch of a sound is related to its frequency, which is measured in hertz (Hz), or cycles per second.

 

Locate the 500-Hz slider, and move it to minus 20 decibels (dB). Click the “play” button for the 500-Hz frequency and listen. Did you hear anything? If so, was the sound loud or soft?

 

The decibel value for a sound wave is a ratio that is used to describe the loudness of that sound compared to a reference value. In this gizmo, a zero decibel sound has the same loudness as the reference sound. The more negative the decibel value, the softer the sound. Therefore, a negative 30 decibel sound is softer than a negative 20 decibel sound.

 

Step 3: Locate the slider for the 4000-Hz sound. (Note that this slider is between the slider for 1000 Hz and 5000 Hz.) Move this slider so that it has the same decibel value as the 500-Hz frequency. Play the 500-Hz sound, and then play the 4000-Hz sound. Does one tone seem louder than the other?

 

Step 4: How loud a sound actually seems, or the perceived loudness, depends on the way your ears function. Human ears can detect some frequencies better than others.

 

Adjust the 4000-Hz slider until it seems to have the same perceived loudness as the 500-Hz sound.

 

Step 5: Repeat Steps 3 and 4 for the remaining frequencies. Start the slider for each frequency at the same intensity as the 500-Hz slider, and then compare the sound to the 500-Hz tone. Move the slider for each frequency up or down as necessary until it has the same perceived loudness as the 500-Hz sound. Note that you may have difficulty hearing any sound at all for a few of the highest and lowest frequencies. This is most likely not because of a hearing problem, but because of the quality of your computer’s speakers.

 

Step 6: Press the “play full sequence” button, and listen to all the tones. Did each sound seem equally loud? If one sound seemed louder or softer than the others, adjust the slider for that frequency and press “play full sequence” again.

 

Step 7: Look at the positions of the sliders from left to right. Imagine connecting the sliders with a smooth curve. What shape would the curve have? This curve is called an equal loudness curve. Click “copy screen” to take a screen shot, and paste the image into a blank document. Post your graph on the discussion board and compare your curve to that of three or four classmates.

 

If it is not possible to compare your graph to classmates' graphs, help members of your family complete the procedure and make equal loudness curves. If possible, have a middle-aged person or a senior, as well as someone your own age and someone several years younger, participate in your lab. Paste all of the curves into your blank document so that you can submit these as data for your lab.

• Were all the curves similar?
• Did some people hear some frequencies differently from others?

Step 8: Now you will create an equal loudness curve for the faintest sound that you can hear at each frequency. For good results in this part of the experiment, the room should be as quiet as possible. By moving the 500-Hz slider and using the 500-Hz “play” button, experiment until you have found the lowest volume at which you can detect a 500-Hz tone. This sound intensity is your threshold of audibility for a frequency of 500 Hz.

 

Step 9: Predict what the intensity of a sound at your threshold of audibility for 4000 Hz will be. Using the same method as you did in Step 8, find the threshold of audibility for a 4000-Hz sound. Was your prediction correct, or was the intensity higher or lower than you expected?

 

Step 10: Find your threshold of audibility for each of the remaining frequencies. The equal loudness curve that results shows the lowest sound intensity that you can hear for each frequency in these conditions.

 

Step 11: Click “copy screen” and paste the screen shot into your document. Post this graph on the discussion board and compare your curve to that of three or four classmates. As before, if that is not possible repeat the exercise with the same people that you had participate in the activity for the equal loudness curve. How do their curves compare to yours? Note: When establishing the threshold of audibility curves, use the same computer and/or the same system settings to ensure a controlled experiment.

 

Observations and Data Collection

 

The properly identified and downloaded curves for you and your experimental subjects will make up your data.

 

Analysis and Discussion

 

What does your personal data indicate?

1. Does your personal data, including both the equal loudness curve and the threshold of audibility curve, appear as a straight line? Why or why not?
   
   
2. If it is not a straight line, which frequencies were easier to hear and which were more difficult to hear?
   
   
3. Were there any frequencies that you could not hear at all?
   
   
4. Compare the two curves of each of your subjects with your own curves. Are there any differences? If so, what does this tell you about their hearing?
   
   
5. What parts of the ear are involved in the process of hearing the different pitches and varying levels of loudness?
   
   
6. Compare the actual results to the predictions that you made before starting the experiment. Were your predictions correct? What factors might have made their curves different? Answer these questions in a paragraph form.

Conclusions

 

From your observations, what can you conclude from this experiment? In this section you should be able to answer the question that was posed in the Problem or Purpose section of this lab.

 

Copy all of your findings and answers for this lab into the space provided in the Module 1: Lesson 6 Assignment.

 

Self-Check

 

To further check your understanding of the pitch and loudness, complete the five questions in the gizmo, and then check your answers.

 

When you have completed the lab, save your assignment in your course folder. You will receive instructions about when to submit your assignment to your teacher later in this lesson.

 

Going Beyond

 

If you found the lab interesting, and you want to learn more about hearing loss, you may want to investigate tinnitus, which is a disorder experienced by many hearing impaired people.

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