How Sound Waves Interact: Definitions & Examples

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  • 0:01 Sound Waves
  • 0:53 Sound Wave Interference
  • 1:15 Constructive Interference
  • 2:00 Destructive Interference
  • 3:17 Beating
  • 4:11 Lesson Summary
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Lesson Transcript
Instructor: Rebecca Gillaspy

Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.

Sound waves move through the air and hit your ear. If sound waves collide, they change the wave and ultimately how you hear the sound. How the wave changes depends on whether the waves meet constructively or destructively.

Sound Waves

If you've ever been to the Grand Canyon, I bet you shouted 'hello' into the canyon to see if you could hear your echo. If you did, you were rewarded with a series of 'hello' responses. An echo happens because the sound waves generated from your shout hit the hard walls of the canyon and get reflected back toward your ears. The same thing would happen if you shouted 'hello' into a wall, however, canyons are more fun because the many rocky surfaces within a canyon cause the sound waves to bounce multiple times, multiplying the number of 'hellos' you get back.

Sound waves do not only interact with objects, they can also interact with other sound waves. In this lesson, we will take a look at the different ways sound waves interact with each other.

Sound Wave Interference

We see from our example of an echo that sound waves are reflected when they hit a solid object. However, when sound waves hit each other, they do not get reflected, instead they blend together. Sound wave interference is the term used to describe the result that happens when sound waves collide.

Constructive Interference

How this interaction affects the waves depends on how the waves meet. If the colliding waves line up in a complimentary way, then they strengthen each other, creating a new and more intense wave. This type of sound wave interference is referred to as constructive interference. In other words, sound waves that are of equal frequency and phase add together to form a wave of larger amplitude.

As you may recall, frequency refers to the rate at which the waves occur, or more specifically, the number of complete oscillations per unit of time, whereas amplitude refers to the height of the waves. The higher amplitude of the new wave will sound louder to you.

Destructive Interference

Sound waves do not always meet up in a way that compliments each other. Sometimes the waves are completely out of sync and end up creating a new and less intense wave. This type of sound wave interference is referred to as destructive interference. In this case, sound waves that are out of phase cancel each other to form a wave of lower or no amplitude. This will sound quiet, or if the wave is completely canceled, you will hear nothing but silence.

In fact, this is how noise canceling headphones work. The headphones are equipped with a small microphone that picks up noise from your surroundings. Electronics within the headphones create a sound wave that is completely out of phase with the surrounding noise. This results in silence.

We also see destructive interference at work in undesired places, like theaters. When multiple speakers are in use within a closed auditorium, the sound waves can interfere with one another. If the sound waves cancel each other, they result in dead spots, or areas where little or no sound is heard. People sitting in a dead spot area would have a lot of difficulty hearing the show.

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