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Strange Noises: Exploring Sounds, Objects, Tones, Music, and Resonance

In this lecture, we delve into the world of strange noises, discussing sounds, objects, tones, music, and the phenomenon of resonance. Learn about vibrations, frequencies, modes of vibration, and how objects can resonate with each other. Discover how sound can cause resonance and the factors that determine the tone of musical instruments. Join us in exploring the fascinating world of strange noises!

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Strange Noises: Exploring Sounds, Objects, Tones, Music, and Resonance

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  1. Lecture 16 Things that make strange noises. October 27, 2004

  2. What’s Wherefore • Exam is distributed. • I normally do NOT curve grades and won’t again, but in this case I think I made some mistakes so I fixed them. • You gan get your “grade” from the syllabus.

  3. Today • Let’s recap some of what we learned. • Sounds • Objects • Tones • Music • In front of us this week • other instruments (very brief) • sounds ……. • then on to • hearing • room acoustics • electricity • microphones • speakers

  4. Let’s recall a few things • DEMO STUFF

  5. Strings L Increasing Frequency Higher Tones

  6. The String Frequencies

  7. String Frequencies fn = (n+1) f0

  8. Sound From the Guitar t=0.005 s t=0.012 s

  9. OP • calculate f

  10. fundamental frequency

  11. Spectrum Expect: 141,282,423,564 Huh??

  12. The Answer …..

  13. Remember the Bar?

  14. Some Facts • All objects resonate at some frequency. • Objects can resonate at different frequencies depending on the structure and the kind of wave we are considering. • A musical sound is something that is “periodic” in time … it repeats itself f times per second with a period of 1/f.

  15. More Bar

  16. This is an example

  17. Another

  18. Fourier’s Theorm Any periodic function can be expressed as a sum of “sine” waves just like the one above.

  19. Example

  20. This can be a sum of sine waves!

  21. Corollary • Any vibration can be formed by a sum of the appropriate sine waves. • Strange stuff!

  22. All objects have multiple “modes” of vibration Transverse Longitudinal

  23. When we hit an object • All modes of vibration are usually excited at the same time. • Some die out quickly • Others are sustained for a longer time. • A guitar string has lots of modes all of which are multiples of a fundamental frequency so the tone is harmonic. • R rock through a glass makes a sound which is clearly NON-HARMONIC

  24. What about a drum??

  25. First Mode of Drum BioWaves, LLC.

  26. Drum

  27. More Thumping

  28. The Drum • Each of these modes are usually excited. • The tension of the drum determines the frequency of each mode. • The modes may NOT be harmonic • Each mode dies out at a different rate. • The player can change the basic “tone” of the drum by changing the tension of the drum head.

  29. Kettle Drum INITIAL Spectrum

  30. The Sonogram

  31. Modes • All modes are excited at first strike. • These vibrations may excite others … resonance. • Each mode decays in a different time. Amplitude time

  32. So … back to the tuning forks RESONANCE !

  33. Objects will resonate when • They are in contact with something that vibrates at its resonant frequency. • Buzz in cars is a good example • Sound can cause resonance if it is at a frequency that is the resonant frequency of another object nearby. • It must have enough energy.

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