Theory Play Share & Discuss

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Teach Ultrasound and Infrasound
with Prisoner of Echo

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Ultra & Infra

Get to know how infrasound, ultrasound, the Doppler Effect and play the acoustics puzzle game Prisoner of Echo!

Teacher Resources

  • Theory: Infrasound, ultrasound, the Doppler Effect.
  • Play: Students play Prisoner of Echo and learn about the science of sound.
  • Share & Discuss: These questions focus on sound and the playing experience.


  • Infrasound is sound with such a low frequency that humans cannot hear it.
  • In nature, infrasound occurs in earthquakes, waterfalls, ocean waves, volcanoes, and a variety of atmospheric phenomena such as wind, thunder, and weather patterns. (source)
  • Some animals, notably elephants, use infrasonic sounds to communicate. An elephant can make such powerful infrasound that it can be detected 10 kilometers away. (source) Gameplay screenshot

Teacher Resources


  • Ultrasound is sound that has such a high frequency it cannot be heard by humans.
  • One important and practical use of ultrasound is in radiology, when pregnant mothers are given ultrasound exams to make sure the baby is healthy.
  • Ultrasound can also be used with a sonar, a system utilized by water vessels (such as ships and submarines) to track the location of other ships and dangerous obstacles such as shallow reefs.

Gameplay screenshot

Teacher Resources

The Doppler Effect

  • The Doppler effect is the phenomenon where a moving object passing by you sounds higher in frequency as it approaches and lower once it moves away from you. In other words, the Doppler effect is observed whenever the source of waves is moving with respect to an observer.
  • Example: a police car driving by you at high speed will initially sound high, but the sound will lower as the car speeds away.

Gameplay screenshot

Teacher Resources


Lesson Goal

  • Play Prisoner of Echo!
  • While you are playing, think how the game represents these concepts:
  1. Infrasound
  2. Ultrasound
  3. Doppler Effect

Are they represented truthfully? Why? Why not?

Gameplay screenshot

How to Play

This game uses Flash. If you see the screen below when starting the game, click on the highlighted Get Adobe Flash Player icon and follow the instructions to install Flash.

Gameplay screenshot

Alternatively, your computer may already have Flash installed, but the game needs your permission to enable it. Click on Allow to run Flash and proceed to the game.

Gameplay screenshot

To begin, click on New Game.

If you are continuing an earlier session, click on Continue instead.

Gameplay screenshot

Select your character by clicking on them. This choice has no gameplay effect.

Gameplay screenshot

Finally, select Confirm to start the game.

Gameplay screenshot

Gameplay Hints

  • If you have trouble completing a room, try restarting it with the Retry button in the top-right corner. You can also take a look at the Dictionary for a better grasp of the concepts!
  • There is no penalty for taking your time while thinking about your move. If you're not sure what you need to do, there's no harm in considering your next move.
  • Remember that you can spend a turn standing still by clicking on your character.

Gameplay screenshot

Share & Discuss

Share & Discuss

  • What did you think of Prisoner of Echo? Do you like it?
  • Did you get to finish the game?
  • Was there any puzzle that gave you a lot of trouble? Which one?

Tasks after Playing

  • The game does simulate the Doppler effect. When?
Show Notes

When the robots move, you can see their sound waves change based on the Doppler effect. The sound waves become of a higher frequency (they are visually "crunched" in-game) in the direction they are moving towards.

  • Look up the hearing ranges (frequencies a species is able to hear) of different animals. What do you find out? What does this mean for humans?
Show Notes

All species have a minimum and maximum frequency that they can hear. Here is a good list of some different species and their hearing ranges.

This means that humans cannot hear all the sounds in nature, and not even all the vocalizations that animals make. A good example is elephants: they are able to emit sounds that are so low that humans cannot hear them.

  • What kind of natural phenomena can cause infrasounds? List as many as you remember!
Show Notes

In nature, infrasound occurs in earthquakes, waterfalls, ocean waves, volcanoes, and a variety of atmospheric phenomena such as wind, thunder, and weather patterns. (source)