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 = ( Tc) 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. Sound Intensity and Resonance
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. where r = distance from source
- 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 / 4πr 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. n=1,2,3,… - IMPORTANT EQUATION Fn = n(v/2L)
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. Fn = n(v/2L) n=1,2,3,… - 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. Fn = n(v/4L) n=1,3,5,… - 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 PRACTICE Harmonics (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.