1. Chapter 15
Sounds

2. 15.1- Properties and Detection of Sound
Importance of Sound

3. Place your hand on your throat.
Speak to someone next to you for 30 seconds.
Sing to someone next to you for 5 seconds.
What do you feel?

4. Movement forward compresses air particles- increases pressure
Movement backwards separates air particles- decreases pressure

5. Sound waves- longitudinal waves with pressure variation that is transmitted through matter (cannot move in a vacuum)
Speed of sound depends on temperature
0.6 m/s per 1oC
343 room temperature sea level
Speeds increase in liquids and solids

6. Echoes- reflected sounds off hard surfaces

7. Detection of Pressure Waves
Human ear takes vibrations in the air and transmits them into electrical impulses

8. Perceiving Sound Pitch- depends on the frequency of the vibration
Human Ear can hear
20 Hz-16,000 Hz
20 Hz-10,000 Hz (older people)
20 Hz-8,000 Hz (age 70-cannot understand speech)

9. Find the wavelength in air at 20oC of an 18 Hz sound wave, which is one of the lowest frequencies that is detectable by the human ear.

10. Loudness- perceived by our sense of hearing, depends primarily on the amplitude of the pressure wave
1 billionth of an atmosphere or 2x10-5 Pa to 20 Pa (pain)
Sound level-logarithmic scale measured in decibels (dB).
10 dB increase is about 2x as loud

12. The Doppler Effect
Doppler Effect- frequency shift

13. Fd=fs(v-vd/v-vs) v=velocity of the sound wave
vd=velocity of the detector
vs=velocity of the sound source
fd=frequency received by the detector
fs=waves frequency

14. Setting up Parameters + from source to detector
- from detector to source
The velocity of sound is always positive!

15. You are in an auto traveling at 25
You are in an auto traveling at 25.0 m/s toward a pole mounted warning siren. If the siren’s frequency is 365 Hz, what frequency do you hear? Use 343 m/s as the speed of sound.

16. A sound source plays middle C (262 Hz)
A sound source plays middle C (262 Hz). How fast would the source have to go to raise the pitch to C sharp (271 Hz)? Use 343 m/s as the speed of sound.

17. 15.2- The Physics of Music

22. Resonance in Air Columns
Closed pipe resonator- a resonating tube with one end closed to air
High pressure reflects back on high pressure
Open pipe resonator- resonating tube with both ends open
Low pressure reflects back on high pressure
Increased amplitude from constructive interference causes the sound to get louder

23. Open Closed
Flutes
Saxophones
Clarinets
Sea Shells

24. Resonance on Strings
Each end is clamped and therefore has a node on each end.
Speed of the wave depends on the tension and mass per unit length.
Must attach to a sounding board (which must resonate as many frequencies) to intensify sound

25. Sound Quality
Tuning fork- uses simple harmonic motion which can be uninteresting
Instruments and Voices- use superposition to blend many frequencies which seems more pleasing to hear
Timbre, tone color, tone quality

26. The sound spectrum: fundamental and harmonic
Fundamental- lowest frequency (f1)
Closed pipe- f1=λ/4
Open pipe- f1=v/2L
Harmonics- multiples of the lowest frequency
Closed pipe- odd multiples
Open pipe- even multiples

27. Consonance and Dissonance
Dissonance- unpleasant set of pitches
Consonance- please set of pitches (pitches with small whole number ratios)
Ex: 1:2, 2:3, 3:4

28. Musical Intervals Octave- 2 notes with frequencies related 1:2
Ex: 440 Hz: 880 Hz
Ex: Fundamental: 1st Harmonic: 2nd Harmonic

29. Beats
Beat- oscillation of wave amplitude

30. Sound Reproduction
Stereo system ,000 Hz frequencies are played with less than 3 dB difference so all notes can be heard
Telephone Hz
Noise- mixture of many frequencies (some say has a calming effect)