In historic times, ear trumpets (also known as ear horns) were made from hollowed-out horns from cows, rams or other animals. In later centuries, engineers experimented with different materials such as silver, brass, ocean shells, and more recently, plastic. To aid in his deafness, composer and pianist Ludwig van Beethoven used many of these devices, which in the 1700s and 1800s, were considered a fashion accessory. Today, the ear horn has been replaced with the modern hearing aid, typically worn in the outer ear.

To achieve the highest quality of amplified sound, engineers experimented with different materials and shapes for ear trumpets over the years. Amplitude measures how much energy a particular wave carries. For humans, amplitude is interpreted as loudness or intensity. A material's ability to transmit sound depends on its properties. For example, stiff plastics and rubber tubing transmit sound energy well, while cloth and porous foam absorb sound energy. In addition, the more layers through which sound waves must travel, the more energy that is absorbed and the quieter the sound seems.

Sound travels at different speeds through different materials, or mediums. The speed of sound depends on the stiffness of the medium (measured by a quantity know as the bulk modulus), as well as its density. Sound travels faster in solids than in gases, and faster in less dense mediums than in denser ones. For example, sound travels faster through a metal rod than it does through air, and faster through hydrogen than oxygen due to hydrogen's lower density.

For more information on the many different designs of modern-day hearing aids, see the associated My Mechanical Ear Can Hear! lesson.

• To introduce the activity, show students ear trumpet images and demonstrate wave propagation by dropping a pebble into a clear tub of water placed on an overhead projector. Recommended sources for images: Ear Wax Museum: http://www.hearingcenteronline.com/museum.shtml and Antique Ear Trumpet Gallery: http://www.deafness-and-hearingaids.net/2007/12/04/antique-ear trumpets/
• Gather materials and make copies of the Shhh… Do You Hear That? Worksheet, and the Sounds All Around Design & Evaluation Worksheet, one each per person.

1. Have students begin by sitting quietly at their desks, filling out the first worksheet (Shhh…), which is intended to help them identify background noises that often go unnoticed. Allow one minute for students to quietly list all the sounds they hear. No talking allowed. Afterwards, ask students what they heard, the pitches of the different sounds and their relative intensities; this helps to clarify the definitions of pitch and amplitude (or loudness).
2. Ask the class to define the problem at hand. Then reiterate by stating the project goal: "Your goal is to engineer an ear trumpet that helps you hear clear, amplified sound when one of your ears is blocked."
3. Have students think of various sounds they can create that have different pitches and amplitudes. (Examples: Zipping up a backpack, snapping fingers, shuffling paper, knocking on a desk, tapping a rubber tub with an eraser, slicing scissors, playing a stereo or musical instrument. Make sure to also include voices.) As a class, for the activity, agree to use 6-8 different sounds that include a good mix of high and low pitches that can be reproduced with the same amplitude each time. Together, categorize these sounds as high pitch or low pitch, On their worksheets, have students and rank the sounds, a-i, according to their amplitudes (a being the most quiet [softest] and i being the loudest).
4. Divide the class into groups of two students each. Have one person be the "listener" and the other the "observer." Have the "observers" stand in a large circle around the room while the "listeners" stand in the middle with cotton in one ear and blindfolds on. The blindfold helps the cotton stay in place and disguises the direction from which the sound originates.
5. Assign the "observers" each one of the pre-determined sounds to make while the "listeners" identify the sound by pointing in the direction from which they heard that sound. (Make this a quiet activity; talking is distracting and unnecessary.) Continue through the a-i list of sounds.
6. Once all the list of sounds have been made, have students fill out Part 1 of the second worksheet, either the "For the listener" or the "For the observer" sections, first writing down the list of sounds, a-i, circling H or L for the pitch of each sound. For this step, the listeners should be evaluating how well they can hear the sounds, while the observers should be watching their partners to see if they can identify the sounds and the directions from which they came. This step provides students with a baseline to which they can compare their ear trumpet design later. Repeat this step again with the listeners and observers switched, so each student has the opportunity to experience the baseline case.
7. Next, have students follow the steps of the engineering design process to engineer their hearing aid devices (ear trumpets):

• Imagine: Introduce the materials available for creating ear trumpets. Give the groups time to think up ideas. (Alternative material distribution idea: Set material prices and give students a maximum budget to spend for each ear trumpet design.)
• Plan: Under the "Plan It!" section of the worksheets, have students draw their agreed-upon team designs and label the materials used for each component of the designs.
• Create: Once designs are teacher-approved, direct student teams to build.
• Test: Once all groups have a device to test, perform steps 4-6 again, using the same sounds as before, and completing the Test It! portion of the worksheets. This enables students to evaluate their designs by ranking how well their devices aided in hearing differently-pitched sounds and voices, and how big of an "ocean-effect" the devices caused, which is considered a design flaw and should be minimized.
• Improve: If time allows, have students make modifications to their original designs. Retest the second design, following steps 4-6 again, recording results on the Improve It! portion of the worksheet. Make sure students recognize their original design flaws and which adjustments improved their ability to hear.

Example student-made hearing aids (ear trumpets). click for copyright

8. Conclude the activity with a class discussion using questions provided in the Assessment section. Ask teams how well their ear trumpets helped them hear and if they could recognize the direction of the sounds more accurately. Have them refer to their evaluations (testing data) as part of the discussion.
9. (optional or assign as homework) Have students complete the Conclusion questions on the last page of their worksheets.

First Worksheet: Have students record their observations on the Shhh… Did You Hear That? Worksheet, which asks them to listen quietly and describe the sounds around them as either soft or loud, low-pitched or high-pitched. Review their answers to gauge their mastery of the subject.

Second Worksheet: Have students follow the engineering design process steps, and document designs and testing results using the Sounds All Around Design & Evaluation Worksheet. After students have finished their worksheets, have them compare answers in a class discussion.

Class Discussion: To conclude, ask the groups how well their ear trumpets helped them hear and whether they could recognize the direction of the sounds more accurately when using them. Have them refer to their worksheet evaluations to compare testing results. Ask the students:

• What shapes worked best? What materials worked best?
• If you had permanent hearing loss, would your ear trumpet be a practical device?
• What makes your ear trumpet difficult to use?
• What properties would an ideal hearing aid device have?