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You might be familiar with this representation of a sound wave:

Sinusoidal wave representation of a sound

This sine wave representation can be a less cluttered way to visualize sound, but it doesn’t show us the actual physical structure of the sound. The following animation shows us this structure:

(1)

This is called a longitudinal wave. Looking at this, it’s much clearer how the Sound travels through the air (or any other medium). Here is how the 2 representations relate to each other:

(3) (2)

A “Sound” or vibration in the air is a density fluctuation that travels through space. The thick, black parts are areas of high density (or energy) and the thinner parts are areas of low density. As the air particles become more dense, they push into the other particles in front of them which is how the vibration travels through space. Physically this is what speakers do to make “Sound”.

You can also see in this video the way sand will settle in the areas of low energy on top of a vibrating metal plate, and how those areas move depending on the frequency that the plate is vibrating. So you can think of music as a coordinated series of air density changes, and it’s our job as producers to create and organize these air density changes in a way that inspires feelings in people.

If you missed them, check out the other articles in this series!

  1. What is Sound?
  2. Listening: How attention changes your perception

References

  1. Astronomy, BYU Physics and. Wave Propagation, acoustics.byu.edu/animations-propagation.
  2. Imgur. “My Speaker Doing The…thing.” Imgur, imgur.com/gallery/dUbY2.
  3. Phase’s Impact on Sonics & Imaging, www.integracoustics.com/MUG/MUG/articles/phase/