1. Sound and Music
Chapters 20 and 21

2. Nature of Sound
Usually results from the vibration of an object which causes the air molecules around it to vibrate.
Rarefaction-area of low molecular density
Compression-area of high molecular density.
Sound must have a medium or else there is nothing to be compressed

3. Sound Characteristics
We can’t perceive wavelength of sound directly.
We sense frequency as pitch.
The higher the frequency the higher the pitch
Ultrasonic are waves too high pitched to hear.
Infrasonic are waves too low pitched to hear.
Amplitude of a sound wave effects loudness.

4. Sound in different media
Sound travels best in mediums that resume their shape after the sound has passed.
The closer the atoms of the material, the easier it is for the sound to pass.
In general, solids are the best sonic conductors and gases the worst.
Speed of sound in air is about 340m/s but can change according to temperature and humidity.

5. Reflection of Sound Waves
Sound bounces off a boundary at the same angle it comes in at.
Called Law of Reflection
Sound reflection is called an echo
Will get some reflection at any change in medium, however, may be too soft to hear.

6. Forced Vibrations
Exerting a periodic force on an object to make it vibrate at a certain frequency
Sounding boards

7. Natural Frequency
The frequency that an object will vibrate at if it experiences a one time force.
Depends on a number of factors like shape and the material
Bells

8. Resonance
When a forced vibration matches the natural frequency of an object, resonance occurs.
Resonance is the drastic increase in amplitude of vibration.
Swings
Tacoma Narrows Bridge

9. Beats
The result of two waves of slightly different frequencies interfering.
A pattern of constructive (loud) and destructive (soft) interference.
The frequency of the beats is equal to the difference in frequency of the two original waves i.e. a wave of 256Hz played with a wave of 260Hz will have a beat frequency of 4Hz.
How instruments are tuned.

10. Intensity Intensity is measured by volume.
Not a linear relationship with our ears. A sound wave with 10 times the strength only sounds twice as loud to us.
That means that damage to the ears can occur with sounds that don’t seem that loud.

11. Harmonics Fundamental-the note that you hear.
Harmonics- Standing waves that have a frequency that is a certain percentage of the fundamental.
The notes in a chord all have specific mathematical relationships between their frequencies.
If something sound dissonant, there is no pattern to the frequencies.

12. Timbre
When you play an instrument, it not only vibrates at the note your hear as the pitch, but also at the higher harmonics.
The unique sound of an instrument (even if a piano and a trumpet play the same note, they sound different.
Caused by a unique combination of higher harmonic strengths.

13. Problems Page 395 Page 408 RQ 3, 5, 6, 9-11, 14, 23-25, 28, 31, 32
Ex 7, 24
Problem 10
Page 408
RQ 3, 12
Ex 8, 18, 19

14. The Voice