CDO 463 1 Basic Acoustics

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CDO 463 1 Basic Acoustics
2012-09-09 17:57:52
Basic Acoustics

Basic Acoustics: Sound Generation and Propagation
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  1. sound narrow definition
    sensation for hearing
  2. sound broad definition
    physical quantity with vibration - periodic or aperiodic - and a pressure disturbance - compressions and rarefractions - and a medium - material for transmitting the sound
  3. periodic
    • regularly repeating
    • ex) tone
    • repeats the same frequency
  4. aperiodic
    • not reguarly repeating
    • 2 types - turbulent and static
    • ex) noise, bullistic, release of stop consonants
  5. Simple Harmonic Motion
    tuning fork
    • produces the simpliest type of sound
    • tine movement : X-Y-X-Z-X-Y-X-Z-X
    • one cycle: X-Y-X-Z-X
  6. Period / frequency
    • amount of time for one cycle / # cycles per second
    • frequency = 1/period or f=1/T
    • physical dimension - observable and measurable
    • Hz
  7. pitch
    the perception of frequency
  8. relationship between frequency/period and pitch
    • increase in frequency = increase in pitch
    • not a 1:1 change/dimension
    • same physical change does not equal the same perceptual change
  9. amplitude
    • force or pressure of sound
    • related to displacement of tine
  10. loudness
    • perception of amplitude
    • decibel dB
  11. relationship between amplitude and loudness
    • increase in amplitude = increase in loudness
    • not a 1:1 dimension
  12. Simple Harmonic Motion
    Uniform Circular Motion
    • another type of SHM
    • circle of radius r
    • point P moves around circle at a uniform speed
    • at each new P, a new radius r' is drawn that forms an angle (theta) with the original r
    • by the time P goes around the circle, theta will go from 0 to 360 degrees
  13. phase refers to
    the angle of theta
  14. period
    time for one revolution
  15. frequency
    # cycles/second
  16. amplitude
    the radius of the circle
  17. Amplitude (X) varies with
    • the sine of theta
    • X = r * sine
  18. waveform
    • graph of displacement as a function of time
    • the waveform associated with SHM is the sine wave because the formula contains the sine function
  19. spectrogram includes
    • time
    • amplitude
    • frequency
  20. spectrum includes
    • amplitude
    • frequency
  21. Simple Harmonic Motion
    • velocity is zero / movement stops at the extremes
    • velcoity is at its max at the point of rest
  22. amplitude graph vs. velocity graph
    the amplitude graph is alays 90 degrees behind the velocity graph
  23. superpositioning of sound waves
    • adding sine waves together
    • go point by point on the x axis and add the y axis numbers together
  24. adding sine waves of equal frequency results in
    • a sine wave with the same frequency
    • creates simple waves
  25. adding sine waves of different frequencies results in
    • complex waves - any wave that is not a sine wave
    • a wave with more than one frequency component
  26. square waves are formed by
    adding the odd multiples of a given frequency
  27. the fundamental frequency is
    • the lowest frequency
    • largest comon multiple in a series of frequencies
  28. harmonics
    frequencies that are integer multiples of the fundamental frequency

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