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The Physics of Sound. By Ryan Waggoner. What is sound?. I n the form a “wave” Must be of a “frequency” that is within the range of hearing Caused by vibration Can be defined as an “oscillation of pressure through a solid, liquid, or gas ” Not only physical, but neurological

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The Physics of Sound

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The physics of sound

The Physics of Sound

By Ryan Waggoner

What is sound

What is sound?

  • In the form a “wave”

  • Must be of a “frequency” that is within the range of hearing

  • Caused by vibration

  • Can be defined as an “oscillation of pressure through a solid, liquid, or gas”

  • Not only physical, but neurological

  • Can be converted into an electronic wave to be modified by transducers such as microphones and speakers

How is sound created

How is sound created?

  • Vibrations. An object vibrates which makes the air molecules around it vibrate and the process is like a domino effect

  • Sound does not travel as an object itself.


  • You cannot “see” sound

The physics of sound

  • We can imagine sound as a 2-dimensional “wave”

  • The wave contains three parts that we care about:

    • Amplitude (soft/loud)

    • Wavelength

    • Frequency (pitch)

The voice

The Voice

  • Using your voice you can show the following changes of a sound wave:

    • Frequency (different pitches)

      • Vocal cords vibrate quicker/slower

    • Amplitude

      • Voice gets louder/softer

      • Caused by the amount of air exerted past the vocal cords

      • Generally controlled by diaphragm

The physics of sound

  • The high and low points on the graph respectively show the areas where molecules of the medium are packed more densely or loosely

  • Audio engineers exploit this to alter sound waves

Direction of sound

Direction of Sound

  • Sound can travel through gases and liquids in longitudinal waves

    • Moves straight ahead

  • Sound is transmitted through solids in both longitudinal waves and transverse waves

    • Transverse waves = alternating shear stress at a right angle from where the sound came from.

Timbre what makes a sound unique

Timbre – what makes a sound unique?

  • Imagine a soccer ball.

  • The vibrations of an object that then result in the vibrating of air molecules have the same effect as a kick, making the air molecules vibrate in different ways

  • Sound bouncing off of a wall generally doesn’t change the sound that much, although it does effect the reverb on sound and how “full” it can be

  • Not determined by wavelength, frequency, or amplitude

Speed of sound

Speed of Sound

  • There is no set speed of sound like there is a speed of light

  • Determined by the medium through which sound travels

  • Temperature and pressure play a role in the speed of sound as well

    STP in air = 343 m/s

    Fresh water = 1482 m/s

    Steel = 5960 m/s



  • A harmonic is a note that has a frequency that is an integer multiple of the “base” frequency.

    • Given a note of a 25 hz frequency, 50 hz, 75 hz, 100 hz, etc.

  • Basically synonymous with an “overtone”

  • Can be heard in choirs or bands when instruments play different but harmonic pitches. A missing note of a chord can be heard, for example.

Sound and the human body

Sound and the Human Body

  • As sound is all about vibrations, those vibrations are taken by the ear drums and converted to “neural action potentials”

  • Audio engineers must take into account not only the physical properties of sound waves, but also the fact that sound is a sensory and perceptual event

    • mp3

Auto tune


  • Audio processing technique that covers up inaccuracies of pitches

  • Digitally modifies the sound wave to blend to the nearest true semitone (or half-step)

  • Has much criticism for not being “real”

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