The ear is a delicate, but powerful sensory organ that assists humans in avoiding danger, communicating with others and enjoying the sounds of the world. Engineers develop audio equipment based on the characteristics of the ear, including its physical shape and psychoacoustic nature. The study of the capabilities and limitations of the ear is extremely important in the production of high-quality audio products, from audio recording equipment to hearing aids. Without this type of research, people who are partially deaf would not have the opportunity to hear any sounds at all.

The ear is a powerful sensory organ that enables humans to detect sound through vibrations in the air, water or other matter. The vibrations are energy in the form of waves of pressure that are collected by the outer ear and funneled into the middle ear. The pressure changes are amplified in the middle ear before reaching the inner ear. Then, the sound passes through the inner ear as hair cells convert the changes in air pressure to a signal of nerve pulses. The pulses are sent through the nerves to the brain where humans acknowledge the sound perceived.

• Make copies of the Frequency Hearing Testing Worksheet, one per student.
• Make sure each computer has Internet access and that the Frequency Hearing Test website simulation works on each computer: http://schubert.ece.drexel.edu/~travis/education/HearingTesting/FreqHearingTesting.html.
• Use headphones or earphones to effectively use the hearing test website; the sounds are too subtle to hear otherwise.
• Practice using the Frequency Hearing Test interface. To operate: click on the desired frequency > push the play button. To increase the volume, use the amplitude adjuster slidebar on the right of the black display box. To pause the waveform as it plays, click the pause button in the upper right corner. To stop playing the sound, click the "stop" button. It helps to use the stop button to stop the sound, before changing to a different frequency. See the worksheet diagram for additional help.

1. Divide the class into teams of four students each. Make sure that the students understand that they are in groups, but must record data individually.
2. Hand out the worksheets.
3. Go through an example of how to use the interface.
4. Have students plug headphones (or earphones) into their computers and make sure the computer volume is adjusted properly.
5. Direct students to open the Frequency Hearing Test website to begin the process of testing for the highest frequency they can hear. URL is http://schubert.ece.drexel.edu/~travis/education/HearingTesting/FreqHearingTesting.html.
6. Have students complete the worksheet, which guides them through an investigation of the waveform for the sounds they are hearing.
7. While students are conducting the hearing tests, write each of the frequencies on the board.
8. After each group has completed hearing tests for each group member, have one representative from each team write down the group's results on the board by placing one tally mark for each team member whose highest frequency heard was that value.
9. Once the data for the class has been recorded, direct students to finish the worksheet, in which they quantitatively analyze the data.
10. Bring the class back together for a short discussion on how this data could be used to help design a hearing aid (which is the last worksheet question).
11. Next, have student teams define the problem for a hearing aid design.
12. Conclude with a post-activity assessment — having students give brief engineering presentations — as described in the Assessment section.

Discussion Questions: Solicit, integrate and summarize student responses to the following questions.

• When I say that dogs can hear sounds at a higher frequency, what does that mean? (Make sure students understand the difference between frequency and loudness. Frequency is a higher pitch. Demonstrate by singing a high and a low note.)
• If you could not hear the high frequency noises that most of us can hear, what kinds of sounds do you think you would miss out on? What if you could not hear low frequency noises?

Worksheet: Have students record measurements and follow along with the activity on their worksheets. After students have finished their worksheets, have them compare answers with their peers. Review their answers to gauge their mastery of the subject.

Presentation: Have students imagine that they are engineering consultants for a medical products company. Using what they learned in the activity, have each team give a two-minute presentation in which they describe to the company their recommendations for their hearing aid design. (Example recommendations: "The hearing aid should improve hearing for the range of 15 Hz to 17 kHz" or "The hearing aid does not need to amplify sound above 17 kHz, since most people cannot hear at this range normally.")