Hands-on Activity: Sound from Left or Right?

Contributed by: GK-12 Program, Computational Neurobiology Center, College of Engineering, University of Missouri

Two identical but inverted photos shows open an open hand placed behind each ear, as if to help direct sound waves into the ears.
Why are two ears better than one?
Copyright © US Department of Veteran's Affairs http://www.warrelatedillness.va.gov/education/healthconditions/hearing-difficulties.asp


Why do humans have two ears? How do the properties of sound help with directional hearing? Students learn about directional hearing and how our brains determine the direction of sounds by the difference in time between arrival of sound waves at our right and left ears. Student pairs use experimental set-ups that include the headset portions of stethoscopes to investigate directional hearing by testing each other's ability to identify the direction from which sounds originate.
This engineering curriculum meets Next Generation Science Standards (NGSS).

Engineering Connection

Biological engineers and neuroscientists perceive human bodies as functioning, controlled systems, not unlike robots. Research is increasingly revealing that mathematical principles similar to those used in robotics are extremely useful or even necessary for a complete understanding of the human body. Engineers use their understanding of the benefits of having two ears and how they help us determine the direction of origins of sounds to design technologies such as radar systems.

Pre-Req Knowledge

  • An understanding of the five senses of the human body.
  • Although not required, we suggest students complete the previous unit in the series, Humans Are Like Robots, and the previous lessons/activities in this unit prior to starting this activity.
  • Conduct this activity after the Hearing: How Do Our Ears Work? activity.

Learning Objectives

After this activity, students should be able to:

  • Describe how having two ears makes it possible to determine the direction of origin of sounds (binaural hearing).
  • Describe the situation in the experimental set-up in which listeners cannot detect the direction of sounds.

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Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

  • Gather and synthesize information that sensory receptors respond to stimuli by sending messages to the brain for immediate behavior or storage as memories. (Grades 6 - 8) Details... View more aligned curriculum... Do you agree with this alignment?
  • Students will develop an understanding of the characteristics and scope of technology. (Grades K - 12) Details... View more aligned curriculum... Do you agree with this alignment?
  • Students will develop an understanding of the relationships among technologies and the connections between technology and other fields of study. (Grades K - 12) Details... View more aligned curriculum... Do you agree with this alignment?
  • Students will develop an understanding of the attributes of design. (Grades K - 12) Details... View more aligned curriculum... Do you agree with this alignment?
  • Describe how new technologies have helped scientists make better observations and measurements for investigations (e.g., telescopes, electronic balances, electronic microscopes, x-ray technology, computers, ultrasounds, computer probes such as thermometers) (Grade 5) Details... View more aligned curriculum... Do you agree with this alignment?
  • Make qualitative observations using the five senses (Grade 6) Details... View more aligned curriculum... Do you agree with this alignment?
  • Explain the interactions between the nervous and muscular systems when an organism responds to a stimulus (Grade 8) Details... View more aligned curriculum... Do you agree with this alignment?
Suggest an alignment not listed above

Materials List

Photo shows a device made from the two metal ear pieces of a stethoscope each attached to clear plastic tubing that runs through metal eyelet screws attached to a piece of wood.
Figure 1. The activity set-up.
Copyright © GK-12 Program, Computational Neurobiology Center, College of Engineering, University of Missouri

Each group needs:

  • stethoscope, the metal headset portion only (the ear tips and ear tubes, without the flexible tubing; see Figure 1 or slide 15)
  • wooden block (12 x ¼ x ¼ inch; 30 cm x 6mm x 6 mm)
  • hard (non-flexible) plastic tube, with ¼-inch inner diameter (ID), 40 cm long
  • 3 eyelet circle screws, with ¼-inch ID, so that the hard plastic tube goes through them
  • clear flexible plastic tube with a ¼-inch outer diameter (OD) and 0.176-inch ID, 1 meter long
  • hot glue, to secure the tube to the wooden block
  • 1-foot ruler, plastic or wooden
  • tape, to secure the ruler
  • pen or pencil, to tap the tube
  • Hearing Pre-Activity Quiz, one per student
  • Directional Hearing Worksheet, one per student
  • Sounds Right Post-Activity Quiz, one per student

To share with the entire class:


Photo shows a teen playing a guitar.
Copyright © 2004 Microsoft Corporation, One Microsoft Way, Redmond, WA 98052-6399 USA. All rights reserved.

(Be ready to show students the Sound from Left or Right? Presentation [a PowerPoint file]. First, administer the three-question Hearing Pre-Activity Quiz, either by handing out paper copies or showing slide 2.)

In what ways is your hearing important to you? (Listen to student responses.) Hearing is one of our most important senses. It allows us to experience and interact with the world in so many different ways. We can experience entertainment such as music, singing, movies and theater. Our hearing enables us to gather information through spoken language and oral communication. It is important to our social relationships with friends and family.

Hearing also helps to keep us safe by alerting us to possible threats in the world around us. One aspect of our sense of hearing is our directional hearing. We can determine what direction sounds are coming from just by hearing them. This ability is very useful in many aspects of our everyday lives.

(Continue on to present students with the content in the PowerPoint file, using the guidance and suggestions provided in the Procedure section.)


binaural: Having (or relating to) two ears.

binaural hearing: How animals use their two ears and the time lag of sound waves to determine direction of origin of sounds.

directional: Related to a direction, that is, sound coming from a direction.

sound localization: A person's ability to identify the location or origin of a detected sound in direction and distance.

stethoscope: An instrument used to listen to heart sounds.


Teacher Notes

  • Present to students the directional hearing content information and detailed concept explanations provided in the 15-slide PowerPoint file using the guidance and suggestions provided below.
  • The worksheet and pre/post quizzes (and answers) are embedded in the presentation and available as separate attachments, leaving it to the teacher to decide how to administer them.
  • Students use an experimental set-up to investigate directional hearing. The set-up consists of a stethoscope headset connected to a flexible tube that is attached to a wooden block with a ruler on it. One student puts the stethoscope in his ears while behind him his partner taps on the tube at random locations. The listener indicates whether the sound is coming from the left or right, responses that the tapping partner records on a worksheet. Then the pair switches roles and repeats the experiment, filling out a second worksheet.

Before the Activity

  • Gather materials and make copies of the worksheet and quizzes.
  • Prepare an experimental set-up for each group following these steps and referring to Figure 1 (also slide 15 in the PowerPoint file):
  1. Place the eyelet screws at each end and in the center of the wooden block.
  2. Run the 40 cm-long hard plastic tube through the eyelet screws, positioning the center of the tube exactly at the middle eyelet located in the middle of the block. Use hot glue to secure the tube in place.
  3. Remove the flexible tubing from the stethoscopes so that only its ear tips with metal ear tubes remain.
  4. Cut the 1 m-long flexible clear plastic tubing into two equal lengths. Insert each (left and right) metal stethoscope ear tube ends into a piece of this flexible clear plastic tubing and then slip the other ends of the flexible tubes into each end of the hard plastic tube attached to the wooden block.
  5. Use tape to attach a ruler to the block with its center mark (at 6-inches) lined up with the center eyelet screw and the center of the tube.
  • Be ready to show the PowerPoint slide presentation to the class.

With the Students

  1. Administer the pre-lesson quiz, which is also provided as slide 2 for showing to students. Slide 3 shows the quiz answers to aid in a class discussion after students have completed their quizzes.
  2. Lead into the topic of directional hearing by presenting the Introduction/Motivation section. Then move into the presentation material.
  3. As necessary, review the mechanics of hearing (slide 4) by going through the steps involved in hearing: sounds enter the ear, tiny middle ear bones amplify sound, cochlea sorts sounds by frequency, nerve passes signal from cochlea to brain stem, signal travels through brain, getting decoded along the way, and the auditory cortex recognizes and processes sound.
  4. Ask the class one of the quiz questions: Why do we have two ears? Then show the answer on slide 5 and explain that having two ears (being binaural) helps us determine the locations of the sounds we hear because of the information the time lag between the two ears provides to our brains. This is called binaural hearing. In addition, our perception of a sound's volume and quality aids in our determination of its source location and distance away.
  5. Sound localization is what we call a person's ability to identify the location or origin of a detected sound in direction and distance. Then explain the role of the time difference in more detail (slide 6) and that of the volume of the sound (slide 7), including our hearing of high- and low-frequency sounds.
  6. Then start the activity by organizing the class into groups of two students each. Allow 30 minutes for students to conduct the activity.
  7. Ask the students: Why do people sometimes turn their heads to determine where a sound is coming from (slide 8)? Listen to student answers to assess how well students have understood the material.
  8. Then challenge students to think of an activity to determine how we detect sounds are coming from, with our eyes closed. Write student ideas on the board for future discussion. Today we are going to perform a testing activity to help us investigate more about directional hearing.
  9. Hand out the worksheets and direct students to write their names on the tops.
  10. Explain the equipment set-up and activity to the groups (slide 9), including a demonstration with two student helpers as well as a review of the worksheet data table (slide 10) so students to know exactly what to do when on their own.

Testing instructions: With his back to the wooden block, one student puts the stethoscope ear tips in his ears while the other, out-of-sight student uses a pen or pencil to tap on the tube at random locations. The listener tries to determine the direction the sound is coming from and says "left" or "right" aloud while the partner (who is tapping) records his directional hearing responses on the worksheet. Then the pair switches roles and repeats the experiment, filling out a second worksheet.

  1. Distribute an equipment set-up to each group and direct them to begin the activity, using the worksheets to guide their data collection and analysis.
  2. After student pairs have completed testing and answering the worksheet results and analysis questions, lead a class discussion to share and explain student findings. Use the worksheet question as prompts (slide 11). Make sure to ask: Did anyone discover regions on the tube where students had difficulty determining the correct direction? (Answer: Yes, an area on the tube exists where we cannot detect the direction of sound.)
  3. Summarize the activity by highlighting the key concepts and reviewing how human hearing works. Also ask the students:

Why do humans have two ears? (Answer: To be able to sense the direction that sounds come from. Sound waves travel at a particular speed, and using simple calculations it can be shown that sound takes 1/500th of a second to travel the distance between the two ears. The hearing system in humans is able to use this difference to determine which ear was closer to the source of the sound. In addition, our ears also use the difference in loudness [or volume] of the sounds between the two ears to ascertain information about their sources. Humans can tell the direction of high frequency sounds better than low frequency sounds.)

How might engineers apply the concepts of binaural hearing to design other useful things? (Answer: Engineers use the idea of how two ears work together and sound wave lags to help determine the direction sound is coming from to design technologies such as radar systems.)

  1. Conclude by administering the post-activity quiz (slide 12, with answers on slide 13).



Pre-Activity Assessment

Pre-Activity Quiz: Administer the three-question Hearing Pre-Activity Quiz (also slide 2, with answers on slide 3) to judge how much students know about the topic prior to beginning the activity.

Activity Assessment

Group Discussion: Have students discuss their findings in groups, particularly if any differences were discovered. How would your hearing be affected if one ear was impaired? (Answer: You would have difficulty localizing sound, that is, determining its direction of origin. Called unilateral hearing loss.)

Post-Activity Assessment

Post-Activity Quiz: Administer the three-question Sounds Right Post-Activity Quiz (also slide 12, with answers on slide 13) with questions similar to the pre-activity quiz, so answers can be used to assess student progress in understanding the concepts presented.

Activity Scaling

  • For younger students, conduct the activity as a class demonstration.
  • For more advanced students, expect them to learn and use all the vocabulary words, and provide them with more explanatory material for the topics (see the websites in the References section).


Chudler, Eric H. The Ear, Neuroscience for Kids. University of Washington. Accessed June 15, 2011. http://faculty.washington.edu/chudler/bigear.html

Ears: How Your Ears Work. Kids' Health, Child and Youth Health, Women's and Children's Health Network, Government of South Africa. Accessed June 15, 2011. http://www.cyh.com/HealthTopics/HealthTopicDetailsKids.aspx?p=335&np=152&id=1463

How Hearing Works. MED-El International, UK (a hearing implant company). Accessed June 15, 2011. (Includes an excellent three-minute narrated video animation of how hearing works) http://www.medel.com/us/how-hearing-works/

Kurtus, Ron. Hearing Direction and Distance. Last revised August 22, 2002. Ron Kurtis' School for Champions. Accessed November 19, 2009. http://www.school-for-champions.com/senses/hearing_direction.htm


Marianne Catanh, Sachin Nair, Charlie Franklin, Satish Nair


© 2013 by Regents of the University of Colorado; original © 2012 Curators of the University of Missouri

Supporting Program

GK-12 Program, Computational Neurobiology Center, College of Engineering, University of Missouri


This curriculum was developed under National Science Foundation GK-12 grant no. DGE 0440524. However, these contents do not necessarily represent the policies of the National Science Foundation, and you should not assume endorsement by the federal government.

Last modified: June 6, 2017