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Understanding Sound: Compression, Rarefaction, Pitch, and Harmonics

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Dive into the fascinating world of sound with a comprehensive exploration of its fundamental concepts. Learn about compression and rarefaction, how we perceive pitch through frequency, and how the speed of sound varies across different mediums like air, water, and ice. Discover the Doppler effect and its effects on sound perception during motion. Uncover the principles of sound intensity and the threshold of hearing, as well as the phenomenon of resonance. Analyze standing waves and harmonic series, and understand how different frequencies interact to create unique sound patterns.

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Understanding Sound: Compression, Rarefaction, Pitch, and Harmonics

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Presentation Transcript

  1. Physics Chp 13 SOUND

  2. Compression vs Rarefaction • Pitch – how we perceive the frequency • Speed depends on medium (air, water, ice) • 3D – goes in all directions

  3. Doppler Effect • As you or the source moves the sound changes. • Towards – higher • Away - lower

  4. Sound Intensity • I = P/A • I = P/ 4πr2 • Threshold of hearing Io = 1x10-12 W/m2

  5. Audible Sounds • Depends on intensity as well as frequency • Resonance is when something vibrates at a natural frequency

  6. Our Ear converts the sound wave into electrical waves so our brain can sense the sound.

  7. Standing waves • Simplest is the fundamental. • On a string it has two nodes and one antinode. • λ1=2L

  8. For a string the first standing wave is half a wavelength and then goes up by whole intergers

  9. Then it increases by additional antinodes • λ2=L • λ3= 2/3L • λ4=1/2L

  10. Since v=fλ and the speed remains const • fn = n v/2L n= 1,2,3….. Harmonic series • f1 is the fundamental

  11. BUT a closed on one end is different • Then the node has to hit the closed end to reflect back with no loss of the wave • fn = n(v/4L) n= 1,3,5……

  12. If you use a mid C (261.6 hz) over a closed tube and get a resonant sound at 0.983 m and 1.64 m, which harmonics are present and what is the likely length for the first harmonic? Assume v = 343 m/s

  13. fn = n(v/4L) n= 1,3,5…… • 261.6 hz = n (343 m/s / 4(0.983m) ) n = 3 • 261.6 hz = n (343 m/s / 4(1.64m) ) n = 5 • So if n is 1 then 261.6 hz = 1(343m/s / 4L) • L = 0.328 m

  14. When two frequencies are slightly off they interfere with each other and create a pattern of changing intensities. The difference in frequencies gives the beat frequency. • f1 = 256hz and f2= 259 hz beat freq = 3hz

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