Hearing Enhancer Instructor Materials

INSTRUCTOR

OVERVIEW OF THIS PROJECT AND WHAT TO EXPECT

In this project, student teams design and construct a device to improve their hearing. The Hearing Enhancers are constructed of only simple materials and are subjected to two testing phases. First, a series of relatively constant volume test sounds is played as the students testing their team's Hearing Enhancer move away from the sound source. Each team scores points when their tester correctly signals hearing a test sound. Next, students testing their design team's device stand in the middle of an imaginary circle and score points for their team by locating the origin of the test sound on the perimeter of the circle.

SPECIFIC PURPOSE OF THIS PROJECT

The most important thing students learn in this project is that engineers design things that enhance people's lives. The specific purpose of this project is to expose students to human-centered engineering. Engineers are interested in helping people. They use their creativity and talents to design devices that intimately interact with humans. Besides learning about sound and hearing, students learn that engineers are closely connected to things we use every day.

THE REAL-WORLD PROBLEM RELATED TO THIS PROJECT

Biomedical, electrical, and materials science engineers design devices that help the physically challenged as well as the unchallenged live more active and meaningful lives. In this project, student design teams learn about sound by designing devices to enhance their hearing. Students must think about the requirements for designing something that interacts with the human body.

SPACE AND TIME REQUIRED

This project can be done in three to five hours and requires a large open area with minimal background noise for testing. An empty football, soccer, or other field will work well if there is no loud machinery or other noise pollution nearby. You may also test the Hearing Enhancers in an auditorium or gymnasium if a good outdoor site is unavailable. However, testing maybe more difficult depending on the size and shape of the room.

MATERIALS AND EQUIPMENT NEEDED

The materials for this project are very easy to acquire. Tell your students what they will be allowed to use and let them gather the raw materials in the week before you plan to do the project. Students may use the following materials to construct their Hearing Enhancers.

• Tin foil

• paper

• glue

• card board

• tape

• milk jug

• two liter bottle

• rubber band

• saran wrap

• glass jar

• soup can

• string

Besides scissors, rulers, pencils and other simple tools for construction, you will need the items listed below to do this project.

• cassette tape recorder and player

• a cassette tape

• stop watch

• 50ft tape measure

• Water pail and sand

• Different shaped pieces of concrete, fabric and wood

SUGGESTIONS REGARDING STUDENT TEAMS

This project is very flexible. Select teams with one, two, or three students. Because there are two phases of testing, students in design teams of two will each get a chance to test their Hearing Enhancer.

PREPARING FOR THIS PROJECT - WHAT TO DO IN ADVANCE

The first thing you need to do in preparation for this project is read the Student Project Description. Acquire the tools and equipment listed above and make sure students have enough of all the raw materials. The next thing you will need to do is practice the demonstrations that are presented in the "IMPORTANT PRINCIPLES INVOLVED" section of this document. Include the demonstrations in your presentation of the project to the students.

Because hearing is effected by so many different factors, such as ambient noise, surrounding structures, temperature, humidity, etc., there are several steps you should follow to ensure good results. The basic purpose of this part of the project preparation is to determine a good starting distance and sound volume for your test site.

Make the Test Sound Recordings

First, obtain a cassette tape player/recorder and a blank tape. For the first stage of testing, you will need a recording of 15 different sounds all at a relatively constant volume and all with a duration of about one second. One way to make these recordings is to tape them off of one television or radio station. Sound clips from familiar television shows or commercials work well. Arrange the 15 sound recordings in groups of three with an empty space of random length, approximately five to eight seconds, between each sound and approximately 15sec of empty space between each group (Fig. 1 a). The random time between individual sounds discourages testers from guessing and the 15sec pause is for the testers to take two steps back before the next series of test sounds starts .

For the second stage of testing, you will need three, 10sec recordings each separated by 10sec of blank space (Fig. 1 b). Recordings of classical or other types music can be used for this stage of testing. The 10sec of music give the testers plenty of time to try and locate the sound source. The 10 seconds of blank space will let the person holding the cassette player move to another location before the next 10 second sound clip begins without having to stop and start the tape. During the second stage of testing, the Stand-in-the-middle phase, it is important for the person holding the cassette player to be very quiet as not give away their location to the tester before the next 10sec sound clip begins.

Figure 1.

This schematic diagram shows two groups and the first six 1sec sound clips for the Line-up phase of testing (a). Your entire recording for the Line-up phase of testing will have five groups and 15 individual sound clips. For the Stand-in-the-middle phase, you will have three 10sec recordings each separated by 10sec of blank space (b).

Determine the Starting Distance and Test Sound Volume

The test sound volume for both testing phases will depend on the starting distance you choose for the first round of the Line-up testing phase. Pick a test site where students can start about 30ft from the sound origin and have at least 20ft to move back away from the sound origin. Determining the best starting distance (not necessarily 30ft) and test sound volume will involve some trial and error, so don't worry if you end up changing the starting distance a couple of times to help find a good test sound volume.

Get three or four students to help you determine the test sound volume. These students are a control group and should not be allowed to use their hands or any devices to help them hear. Have the students stand blind folded at a distance of about 30ft from the cassette tape player and ask them to give a knee bend when they hear a test sound. Play the test sound recording that you made for the Line-up phase of testing and watch the students' responses. Have them move closer to, or further from the sound source until you find a volume that all the students can hear. Reduce the volume very slowly until none of the students can hear it. Note very carefully this volume and the distance the student are from the sound source. Use this volume during the entire testing procedure. Use this distance as both the starting distance for the Line-up phase and as a basis for determining the radius of the imaginary circle in the Stand-in-the-middle phase.

GUIDELINES FOR TESTING THE SYSTEMS CREATED

First, there is the Line-up phase of testing (Fig 2) in which one person from each design team stands in a line and tests their enhanced ability to hear a constant volume sound from increasing distances. In the Line-up phase, ask the testers to give a knee bend to signal they heard the test sound. Teams score points each time the person testing their device correctly signals hearing a sound. Record the testers' signals and verbally instruct them to take two steps back after each sound clip group. If the tester signals when there is no sound being played, deduct points as described below.

Figure 2.

In the line-up phase of testing, the number of times the tester correctly signals hearing a constant volume test sound along with the distance it was heard from will be used to calculate the design's performance.

Next, there is the Stand-in-the-Middle phase (Fig 3) which involves one person from each team standing in the middle of an imaginary circle and determining, with the help of their Hearing Enhancer, the location of the sound source on the perimeter of the circle. The tester for each team will stand in the middle of an imaginary circle and while three, 10sec test sounds are played, they must locate the source the of the sound on the perimeter of the circle. In the Stand-in-the-Middle phase, ask testers to point to the sound source.

Figure 3.

In the Stand-in-the-middle phase of testing, the tester uses their team's Hearing Enhancer to determine what direction the test sound is coming from.

To measure the accuracy of each tester's prediction about the location of the sound source, instruct two people to stand an arm distance away from the person holding the sound source. Instruct two more people will stand an arm distance from them. When the tester points to the direction they think the sound is coming from, the four people standing by the sound source will help decide how much error was in the tester's prediction. If the tester points directly to the person holding the sound source, their team receives 1000 points. If the tester points to either of the persons next to the sound source, their team receives 750 points. And finally, if the tester points to either of the persons standing the furthest away from the sound source, their team receives 500 points. Remember, each tester will get three attempts at locating the sound source. Between each 10sec sound clip move to another location on the circle. During both stages, blind fold the people testing Hearing Enhancers.

Two performance indexes may be calculated to evaluate the performance of each team's Hearing Enhancer. Calculate the Basic Performance Index (BPI) by using results from the Line-up phase of testing. Calculate the Extra Performance Index (EPI) by using the results from both phases of testing.

IMPORTANT STEPS IN MANAGING THE PROJECT

1. Divide the class into design teams.

2. Distribute the Student Project Description.

3. Present the project to the students (15-30 minutes).

4. Let the students read the materials, discuss it among themselves, ask questions, and generate design ideas (20-30 Minutes).

5. Have students present their ideas or comment on their proposed designs.

6. Let the design teams work on prototypes and experiment (30-60 Minutes).

7. Test the working prototypes. Discuss the possible reasons for successes or failures during testing (30-60 Minutes).

8. Let the students improve their prototypes or redesign and reconstruct (30-60 Minutes).

9. Test the final designs (30 Minutes).

10. Summarize the results of the project and tie the concepts together in a positive closure (30 Minutes).

IMPORTANT PRINCIPLES INVOLVED

The most important principles involved in this project belong to the science of waves. Sound waves only exist in matter; sound does not travel in a vacuum. Just like water waves, even though the water itself doesn't move very far as the wave passes, the material a sound wave travels through doesn't move very far even though the wave travels with a definite velocity (344m sec-1 in air and 1484m sec-1 in water). Waves have a oscillation frequency (the number of cycles per second called Hertz, Hz) and amplitude (the height of the wave). Humans hear sounds with frequencies between 20 and 20,000Hz. These three equations relate the frequency, f, of a sound to its wave length (lambda).

Water waves are different from sound waves because they rely on gravity to exist and involve an interface of two different fluids. Sound waves are actually waves of changing pressure. But, like water waves, two different sound waves will interfere (add to make a larger wave, or cancel to make a smaller one).

Figure 4. After you place the material in the water, drop BB's at one end and observe the behavior of the waves as they are reflected from the material.

Reflectors of sound and water waves are used in many applications and can be demonstrated with a large pail of water, some pieces of common materials and some BB's. To demonstrate how waves are reflected from different surfaces, use a rough and jagged piece of concrete, a soft and fluffy piece of fabric, and a smooth piece of wood or Formica. For best results, create a sand bank perimeter in bottom of the pail to act as a non-reflecting border. Use only a small amount of water in a setup like that shown in figure 4. Use this demonstration to make the connection between circular waves and straight line rays.

Figure 5.The law of reflection says that the angle both rays make with the reflecting surface are equal.

Figure 6.For sound waves going from 1 to 2, the amplitude of the sound wave decreases due to "geometric attenuation.".

The first thing your students need to know before they can use an acoustic reflector is that if the wavelengths of the sound wave are very small (equivalent to saying the frequency is very large) in comparison with the reflecting surfaces they are interested in, they can use simple geometry to analyze them. Use the equations above to calculate the wavelengths of several different frequencies and discuss it with the students in terms of what types of sounds will be easily reflected. The law of reflection applies to curved surfaces like cones and parabolas. Include some curved surfaces in your demonstration.

Horn shapes have been used for a very long time to improve the radiation or reception of sound waves. Keep in mind that for very high frequencies (>105), a wave generated in the throat (point 1) of the horn is propagated as a free sound beam near the axis without being influenced significantly by the walls of the horn. But, for lower frequencies, the resistance to the sound radiation is influenced by the shape of the horn walls (Fig 6.). One basic reasons why the horn works is that the area at opening 2 is greater than at opening 1 which makes a sound wave entering at 2 more concentrated (more energy per cross sectional area) at 1. Effective horns have very hard, smooth walls that absorb as little sound energy as possible.

A simple horn is not an extremely effective way to locate sounds because it is open to capture sounds from so many directions. Devices like the one shown in figure 7 have been used as directional sources and receivers of sound. Only the sound waves entering from a direction parallel to the tubes do not cancel each other out at the other end. When two waves from a source take two paths, one could get ahead of the other and would be called out of phase. In a tube, the phase velocity of a sound wave is practically equal to free sound speed, therefore all components of the sound wave through the tubes arrive in phase.

Figure 7. A tubular microphone works because the phase velocity of sound in a tube is practically equal to the free sound speed. Sound waves that do not enter the microphone in a direction parallel to the tubes will not arrive in phase at the other end. Therefore, these waves interfere and the result is they cancel each other out.

PROVIDING SUCCESSFUL CLOSURE

The most important thing you can emphasize to the students is that the activity they have just completed is very much like the activities that engineer are involved in. Biomedical and other engineers are interested in helping people and they show this through design.

SPECIAL SAFETY CONSIDERATIONS

This project is very safe if you make sure no student puts anything in their ears.

This project was developed by Eddie Richert.