# CDO 463 2 Basic Acoustics

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1. tuning forks amplitude is determined by
the strength of the initial blow
2. a tuning forks energy is used up
because of damping - friction within the fork itself and friction against the air molecules being moved imparts energy into the medium
3. inverse square law
4 part
• intensity of sound is expressd as force/area
• as the wave moes away from the source it covers a greater and greater area
• however the wave has a finite amount of force
• the intensity varies inversely with the square of the distance from the source
4. What 4 things can happen when a sound wave strikes an object
• reflection - a bouncing back of a wave in the opposite direction of the original or incident wave
• absorption - reduction in the amount of sound energy due to phyical characteristics of the struck object
• transmission - movement of the wave through the struck object
• diffraction - spreading apart of a wave as it encounters obstacles
5. reflection
• portion of a wave bounces back when it hits an object
• echo or reverberation
• will be of a smaller amplitude than the original wave
6. absorption
• reduction in the amount of sound energy
• similar to damping
• acoustic energy dissipated as heat
• amount varies depending on the object struck
7. poor absorbers v good absorbers
• poor - hard, smooth surface
• good - soft, rough surface
8. standing wave
interference between an original and a reflected wave
9. interference is the result of
the addition of two or more waves
10. constructive interference
waves reinforce each other increasing amplitude (pressure)
11. destructive interference
waves cancel each other, decreasing amplitude (pressure)
12. node
that point in the standing wave where the pressure of the original wave is always equal and opposite the pressure of the reflected wave
13. antinode
the point in the standing wave that undergoes maximum variation in pressure (mx negative to max positive)
14. The complete wavelength of a standing wave is composed of
three nodes and two antinodes
15. Guitar strings:
increase mass
more tension
increase length
• decrease frequency
• higher frequency
• decrease frequency
16. Vocal folds
increase mass
more tension
increase length
• decrease frequency
• high frequency
• increase frequency (because you lower the mass)
17. guitar strings
wavelength =
• wavelength = 2L
• (L = length)
18. guitar strings
frequency =
f = c/wavelength

• f = square root of (t/m) / 2L
• (t = tension) (m = mass)

or

f = 1/2L * square root (t/m)
19. Higher mode of vibration give rise to
overtones, or harmonics, that are at even and odd integer multiples of the fundamental frequency
20. harmonic structure is the combination of
fundamental frequency and harmonics, and their amplitudes
21. the vocal tract is essentially a
column of air in a tube that is open at one end (the lips) and closed at the other end (the larynx)
22. air columns
f =
• f = 1/4L * c
• c = square root (E/p)
23. Harmonic structure of the sound produced by the air column is
• a fundamental frequency and harmonics that are at the
• odd integer multiples of the f0.
24. Harmonic structure
the combination of a sound's fundamental frequency and harmonics and their amplitudes
25. showing of harmonic structure
spectrum - desription of the amp and frequency characteristics of a sound wave
26. sound quality is determined by
the harmonic structure of the sound
 Author: shanamd2011 ID: 174819 Card Set: CDO 463 2 Basic Acoustics Updated: 2012-10-01 23:37:48 Tags: Absorption Reflection Folders: Description: Absorption and Reflection Show Answers: