1. Chapter 15 Notes
Sound

2. Section 15.1 Objectives
Explain how sound waves are transmitted through the air.
Relate the physical properties of sound waves to our perception of sound.
Use the Doppler effect to explain changes in pitch as objects move toward and away from you.

3. Sound Waves
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4. Characteristics of Sound Waves
Speed
Frequency

5. Practice Problem
Find the wavelength in air at 20°C of an 18 Hz sound wave, which is one of the lowest frequencies that is detectable by the human ear.

6. Detection of Pressure Waves
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7. Loudness
Decibel Scale

8. The Doppler Effect
The change in the frequency of sound caused by the movement of either the source, the detector, or both

10. Example Problem
A trumpet sounds C above middle C (524 Hz) while traveling in a convertible at 24.6 m/s. What is the frequency of the sound the observers hear as the convertible moves toward them? Assume that the temperature is 20°C.

11. Section 15.2 Objectives
Differentiate between open- and closed-pipe resonators.
Apply the concept of resonance to air columns and strings.
Explain why there are variations in sound among instruments and among voices.

12. Types of Instruments Vibrating strings Open-end air columns
Closed-end air columns
Vibrating mechanical systems

13. Lowest 3 Natural Frequencies of String Instruments
Resonance on Strings
Lowest 3 Natural Frequencies of String Instruments

14. Resonance on Strings
Natural frequency an object vibrates depends upon:
Tension
Density
Length

15. Resonance in Air Columns
The tubes that make up a wind instrument contain an air column where a standing wave is produced.
Open-pipe resonator
Closed-pipe resonator

16. Sound Quality Fundamental Harmonics
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17. Beats