Module 1 Lesson 3 - 5 (Lab)
Lesson 3 — Mechanoreception: The Ear
Lab — Hearing: Pitch and Loudness
Introduction
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 might have observed animals that seemed agitated by sounds that
you could not hear.
You may have heard an older person say, "Speak into my good ear." The range of sounds that we can hear decreases as we age, especially if we are exposed repeatedly to loud sounds from lawnmowers, snowmobiles, machines, constant heavy traffic,
sirens, loud concerts, and such devices as MP3 players, iPods, and televisions that are very loud.
The pitch of a sound is related to its frequency, which is measured in hertz (Hz), or cycles per second.
The decibel value for a sound wave is a ratio 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 is. Therefore, a negative 30 decibel sound is softer than a negative 20 decibel sound.
Problem
What is your threshold of audibility for various frequencies?
Optional activity: Have friends or family members try this as well, and then compare results.
Materials
No additional materials are required other than access to the Frequency and Volume Gizmo.
Prediction
Predict how you will compare with the average population.
If you are comparing with family or friends, then 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 the curves
will be as you have predicted.
Procedure
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First, eliminate any background noise.
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Be sure the system volume slider is set to 1 and click the test button. Adjust the system volume slider until a comfortable volume is reached.
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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?
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Locate the slider for the 4000 Hz sound. Move this slider to minus 20 dB. Play the 500 Hz sound, and then play the 4000 Hz sound. Does one tone seem louder than the other is?
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Adjust the 4000 Hz slider until it seems to have the same perceived loudness as the 500 Hz sound.
- Repeat Steps 4 and 5 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.
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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.
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Compare your curve to those of your friends or family members.
Observations and Data Collection
Your data are the equal loudness curves for you and other people of various ages that participated in your experiment.
Analysis and Discussion
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What does your personal data indicate?
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Does your personal data, including both the equal loudness curve and the threshold of audibility curve, appear as a straight line? Explain reasons for this.
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If it is not a straight line, which frequencies were easier to hear and which were more difficult to hear?
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Could you not hear some frequencies at all?
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Compare the two curves of each of your subjects with your own curves. Are any differences apparent? If so, what does this suggest about their hearing?
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What parts of the ear are involved in the process of hearing the various pitches and varying levels of loudness?
Consider the curves carefully. The lowest curve indicates the minimum intensity for hearing and the highest is the upper limit for hearing. At the lower levels, listeners might feel a tickle. The highest level will be uncomfortable or painful. Do not expose your ears to sounds above 120 dB because this damages your hearing.
The graph curves down between 1000 Hz and 5000 Hz, and it is the lowest at 4000 Hz. This indicates that our ears are the most sensitive between 1000 Hz and 5000 Hz, with 4000 Hz being the most sensitive frequency.
Were you able to hear the 16000 Hz tone? Many adults cannot hear the tones at high frequencies. The hair cells in the organ of Corti do not regenerate after they are damaged. Hearing loud noises causes a strong movement in the basilar membrane that damages the hair cells.
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 section of this lab: What is your threshold of audibility for various frequencies?
Online Assignment - Self-Check
To check further your understanding of the pitch and loudness, complete the five online questions in the Gizmo lab, and then check your answers. Your answers are not required for marking.