More On Sound

1
More On Sound
2
Quality

• How you can tell one sound source from another
  even when playing the same frequency
• Depends on the presence of overtones

3

• Tuning Fork
• Guitar

4
Noise

• Unpleasant combo of overtones

5
Sound Interference

• When sound waves travel through the same space,
  they interfere with one another
• In some places they interfere constructively and
  the sound intensity is amplified
• In some places they interfere destructively and
  intensity is decreased
• Constructive interference occurs every whole
  wavelength while destructive interference occurs
  every ½ wavelength

6
Beat

• When two sounds are close in frequency they can
  interfere with one another over time
• You will hear alternating loud and and soft
  sounds

7
(No Transcript)
8
Beat Frequency

• Number of loud sounds heard per second
• B ? f2 f1?
• Human ear can only detect beat frequencies less
  than 7 Hz (difference in frequency of 7 Hz)
• Used to tune instuments

9
Example

• A tuning fork produces a steady 400Hz tone. When
  struck and held near a guitar string twenty beats
  are counted in 5 seconds. What are the possible
  frequencies of the guitar string?

10
Mach

• Supersonic Speed faster than sound
• Mach ratio of speed of an object to the speed
  of sound
• Mach speed/ speed of sound

11
Example

• What is the speed of a plane traveling at Mach 3?

12
Sonic Boom

• When an object approaches the speed of sound,
  circular wave fronts pile up in front
• At point of pile up, air pressure is high
  called the Sound Barrier (lots of turbulance)
• Once past the sound barrier, wave fronts pile up
  along the side
• Constructive interference creates high pressure
  area which sweeps the ground Sonic Boom

13
(No Transcript)
14
(No Transcript)
15
Doppler Effect
16
What Is It?

• Pitch of an object appears to change as it passes
  a stationary observer
• In front of moving object, waves pile up creating
  area of higher frequency
• Behind waves spread out, lower frequency

17
(No Transcript)