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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

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

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 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”