2. Chapter 26 SOUND

3. All Sounds are produced by the vibrations of material objects.

4. Saxophone: vibrating reed Voice: vibration of vocal cords Piano or guitar: vibrating strings Flute: fluttering column of air at mouthpiece.

5. Pitch: subjective impression about the frequency of sound. We normally hear between 20 and 20000 Hertz.

6. Infrasonic: sound waves below 20 hertz Ultrasonic: sound waves above 20000 hertz we can not hear ultra or infrasonic sound waves

7. Sound is a Longitudinal wave.

8. Sound is also a pressure wave. Because of the longitudinal motion of the air particles, there are regions in the air where the air particles are compressed together and other regions where the air particles are spread apart.

9. Compression: a pulse of compressed air (….when you quickly open a door it pushes the air that direction.)

10. Rarefaction: a disturbance in air in which the pressure is lowered. (….when you shut a door it pulls the air toward the door.)

11. For all wave motion, it is not the medium that travels across the room, but the pulse that travels

12. Transmissions of Sound: Air is the slowest at transmitting sound. Water is in the middle and Solids are the best…… vsolids > vliquids > vgases

13. The Speed of Sound: in dry air at 0°C is about 330 meters per second or about 1200 kilometers per hour. This is about 1 millionth the speed of light.

14. This is why you see lightening before you hear thunder.

15. An increase in the temperature of water vapor will increase the speed of sound. For every degree increased sound will travel faster by 0.60 m/s.

16. Speed of sound through materials depends on the elasticity of the materials.

17. Elasticity: ability of a material to change shape in response to an applied force, and then resume its initial shape once the distorting force is removed.

18. Steel is very elastic and putty is inelastic. In elastic materials the atoms are relatively close together and respond quickly to each other’s motions. Sound travels about 15X’s faster in steel than in air and 4X’s faster in water than air.

19. The intensity of the sound is proportional to the square of the amplitude of the sound. It is measured by an oscilloscope. (page 394)

20. Loudness: is a physical sensation sensed in the brain. It is subjective but is related to sound intensity.

21. The unit of intensity for sound is the decibel (dB).

22. Decibel Ratings: It starts at 0 for the hearing threshold. Then 10 dB which is 10X as intense as 0. 20 dB is not twice as intense as 10dB but 10X as intense as 10dB or 100X as intense as 0dB.

24. Source Intensity Level # Times Greater Than TOH Threshold of Hearing (TOH)0 dB10 0 Rustling Leaves10 dB10 1 Whisper20 dB10 2 Normal Conversation60 dB10 6 Busy Street Traffic70 dB10 7 Vacuum Cleaner80 dB10 8 Large Orchestra98 dB10 9.8 Walkman at Maximum Level100 dB10 Front Rows of Rock Concert110 dB10 11 Threshold of Pain130 dB10 13 Military Jet Takeoff140 dB10 14 Instant Perforation of Eardrum160 dB10 16

25. Forced Vibration: Vibration of an object that is made to vibrate by another vibrating object near by.

26. The sounding board in a musical instrument amplifies the sound through forced vibration. A guitar would be barely audible without the sounding board. All stringed instruments use sounding boards.

27. Natural frequency: Frequency at which an elastic object once energized will vibrate.

28. Resonance: to resound, or sound again radio stations tune into a certain frequency and resonate at that frequency.

29. In 1831 an infantry troop marched across a bridge and caused the bridge to collapse. They marched at the natural frequency of the bridge causing it to resonate and fall. Now military personnel “break step” when crossing a bridge.

30. Interference: affects the loudness of sounds through constructive and destructive interference.

31. Beats: the periodic and repeating variations in the loudness of sound.

32. Important note: the graphs on the following page represent sound as a transverse wave. This is for a better understanding of the concepts addressed. Remember ….. Sound is a longitudinal wave.