CHAPTER 13

1. CHAPTER 13 Sound

2. SECTION 13-1 Sound Waves

3. - The Production of Sound Waves

4. - The Production of Sound Waves • Sound Waves are longitudinal.

5. - The Production of Sound Waves Sound waves cause compression and rarefaction of air molecules as they travel through air

6. - Characteristics of Sound Waves Audible sound waves (that humans hear) range between 20 to 20,000 Hz

7. -The Human Ear

8. -Hearing Loss

9. - Characteristics of Sound Waves Frequency determines pitch (how we perceive the sound to be).

10. - Characteristics of Sound Waves Frequency determines pitch (how we perceive the sound to be).

11. - Characteristics of Sound Waves • Speed of Sound depends on the medium. • Speed also depends on the temperature of the medium: vsound = (331 + 0.6Tc) m/s

12. - Characteristics of Sound Waves Sound waves propagate in three dimensions.

13. - Characteristics of Sound Waves Because of sound’s spherical nature, we can examine intensity levels from a point source center

14. - The Doppler Effect • Relative motion creates a change in frequency.

15. - The Doppler Effect • Relative motion creates a change in frequency. fo = f(v+ vo) / v + vs) Highest Sound? Observer and source running toward each other Lowest Sound? Observer and source running away from each other

16. - 13-1 Important Vocabulary • Compression: the region of a longitudinal wave in which the density and pressure are greater than normal. • Rarefaction: the region of a longitudinal wave in which the density and pressure are less than normal. • Pitch: how high or low we perceive a sound to be, depending on the frequency of the sound wave. • Doppler Effect: frequency shift that is the result of relative motion between the source of waves and an observer.

17. SECTION 13-2 Sound Intensity and Resonance

18. - Sound Intensity • Intensity and frequency determine which sounds are audible.

19. - Sound Intensity • Intensity is the rate of energy flow through a given area. I = ∆E/∆t per unit area J/s/area → Power/area → Watts/m2 For a SPHERICAL WAVE, energy propagates in all directions. The Spherical surface is 4πr2

20. - Sound Intensity I = ∆E/∆t per unit area J/s/area → Power/area → Watts/m2 For a SPHERICAL WAVE, energy propagates in all directions. The Spherical surface is 4πr2 Power / 4πr2 where r = distance from source

21. - Sound Intensity Power / 4πr2 where r = distance from source

22. - Sound Intensity The softest sound at 1000 Hz = threshold of hearing I = 1.0x10-12 W/m2 The loudest sound the ear can tolerate = threshold of pain I = 1.0x100 W/m2

23. - Sound Intensity Relative intensity, or decibel level, is measured in decibels. dB = 10 log I/Io I = intensity (W/m2) of sound being heard Io = threshold of hearing for the same frequency

24. - Sound Intensity – the Decibel Scale

25. - Sound Intensity – the Decibel Scale

26. - Forced Vibrations and Resonance A forced vibration at the natural frequency produces resonance.

27. - 13-2 Important Vocabulary • Intensity: rate at which energy flows through a unit area perpendicular to the direction of wave motion. • Decibel Level: relative intensity, determined by relating the intensity of a sound wave to the intensity at the threshold of hearing. • Resonance: a condition that exists when the frequency of a force applied to a system matches the natural frequency of vibration of the system.

28. SECTION 13-3 Harmonics

29. - Standing Waves on a Vibrating String • Harmonics are integral multiples of the fundamental frequency.

30. - Standing Waves on a Vibrating String Harmonics are integral multiples of the fundamental frequency.

31. - Standing Waves on a Vibrating String Harmonics are integral multiples of the fundamental frequency.

32. - IMPORTANT EQUATION • Harmonic Series of Standing Waves on a Vibrating String Fn = n(v/2L) n=1,2,3,… • frequency = harmonic # x (speed of waves on string) (2)(length of vibrating string)

33. - Standing Waves in an Air Column • If both ends of a pipe are open, all harmonics are present. • If one end of a pipe is closed, only odd harmonics are present. • Harmonics account for sound quality, or timbre. • Fundamental frequency determines pitch.

34. - Standing Waves in an Air Column

35. - IMPORTANT EQUATION • Harmonic Series of a Pipe open at both ends Fn = n(v/2L) n=1,2,3,… • frequency = harmonic # x (speed of waves in pipe) (2)(length of vibrating air column)

36. - Standing Waves in an Air Column

37. - IMPORTANT EQUATION • Harmonic Series of a Pipe closed at one end Fn = n(v/4L) n=1,3,5,… • frequency = harmonic # x (speed of waves in pipe) (4)(length of vibrating air column)

38. - Standing Waves in an Air Column

39. - Beats • Sound waves at slightly different frequencies produce beats. • The number of beats per second corresponds to the difference between frequencies.

40. - Beats

41. - LET’S PRACTICEHarmonics (Open Pipe) • Given: L= 2.45 m, v =345 m/s, f1-3=? • Step 1: Choose OPEN equation: Fn = n(v/2L) • Step 2: Fn = (1)(345/2(2.45))= 70.4 Hz • (2)(345/2(2.45))= 141 Hz • (3)(345/2(2.45))= 211 Hz

42. - LET’S PRACTICE Harmonics (Open Pipe) • Given: L= 4 m, v = 777 m/s, f1-3=? • Step 1: Choose OPEN equation: Fn = n(v/2L) • Step 2: Fn = (1)(777/2(4)) = 97.1 Hz • (2)(777/2(4)) = 194 Hz • (3)(777/2(4)) = 291 Hz

43. - 13-3 Important Vocabulary • Fundamental Frequency: the lowest frequency of vibration of a standing wave. • Harmonic Series: series of frequencies that includes the fundamental frequency and integral multiples of fundamental frequency. • Timbre: the quality of a steady musical sound that is the result of a mixture of harmonics present at different intensities. • Beat: interference of waves of slightly different frequencies traveling in the same direction, perceived as a variation in loudness.