1. SOUND CHAPTER 12

2. All Sound Has 3 Aspects… 1.Source 2.Energy 3.Detected Sound is Longitudinal Waves (Compression Waves) Sound must have a medium. Sound can’t travel in the absence of a medium

3. Sound travels differently in different media –Hear under water –Along train tracks –Localize Speed of Sound –Air 0° 331m/s –Air 20° 343m/s –Water 1440m/s –Iron 5000m/s Generally if density is increased, speed is increased! - What about air 0° + 20°C ??

4. Table 12-1 Speed of Sound in various materials at 20°C and 1atm Material Speed (m/s) Air Air(0°C) Helium Hydrogen Water Seawater Iron and Steel Glass Aluminum Hardwood 343 331 1005 1300 1440 1560 approx 5000 approx 4500 approx 5100 approx 4000

5. Loudness : Energy in a wave... Loosely Amplitude Pitch or Frequency : # of Vibrations per second –High – Flute –Low – Tuba Humans can hear a range of frequencies 20Hz to 20,000Hz – Humans20Hz to 20,000Hz – Humans Above 20,000 Hz – Bats Ultra SonicAbove 20,000 Hz – Bats Ultra Sonic Below 20Hz – Elephants Infra SonicBelow 20Hz – Elephants Infra Sonic

7. Sound Intensity (B) The unit for loudness is the Bel -- named after Alexander Gram Bell. The unit was too big so we commonly refer to a 1/10 of a bel dB = decibel The dB scale is logarithmic- it begins at 0 – the quietest sound that can be heard Doubling sound intensity corresponds to an increase in dB of 3

8. 10x intensity gives an increase in dB of 10 100x intensity corresponds to dB increase of 20 a 50 dB is 100 times more intense than a 30 dB Pg. 351 has various sound levels space shuttle 170dB see chart THE EAR see model

9. Source of the sound TABLE 12-2 Intensity of Various Sounds Intensity Level (dB) Intensity W/m 2 Jet Plane at 30m Threshold of Pain Loud Indoor rock concert Siren at 30m Auto Interior, moving at 90km/h Busy Street Traffic Ordinary conversation, 50cm Quiet Radio Whisper Rustle of Leaves Threshold of hearing 1401201201007570654020100 100 1 1 x 10 -2 3 x 10 -5 1 x 10 -5 3 x 10 -6 1 x 10 -8 1 x 10 -10 1 x 10 -11 1 x 10 -12

10. Musical Instrument Pitch is determined by the lowest frequency. (fundamental) F 1= ½λ F 2= λ F 3= 3/2λ

11. Overhead Picture- Guitar Changing the length of a vibrating string (column of air) changes the frequency (Pitch)Changing the length of a vibrating string (column of air) changes the frequency (Pitch) The velocity is the same on each string so F is inversely proportional to lengthThe velocity is the same on each string so F is inversely proportional to length

12. Wind Instruments TromboneTrumpetTuba Pressing valves changes L of air column

13. Bugle – no moving parts, octave increments Sounding Board

14. Moving air in a column is a musical instrument. The frequencies that persist are the ones that correspond to standing waves -Regarding Molecules of air Nodes represent NO motion of air molecules Antinodes represent the most displacement.

15. Tubes, Open and Closed OPENFluteClosedClarinet We can explain BOTH in terms of… 1.Displacement of air 2.Pressure

16. OVERHEAD Figure 12-12 Standing waves in open-open tube

17. Overhead Figure 12-13 Standing Waves in open- closed tube

18. Quality of Sound Quality of sound : timbre – tone color Quality is determined by overtones Quality happens by superposition of waves ConstructiveDestructive Interference

19. Oscilloscope Sum of ALL THREE 1 2 3

20. Interference of Sound Waves 12-7 Fig 12-17 Fig 12-18 Beats Fig 12-19 Doppler Effect Fig 12-20 Example probs: 12-13 12-14 Pg. 368 Red Shift Shock Waves Fig 12-24

21. Fig 12-20 OVERHEAD Fig 12-21 Overhead Fig 12-17, 12-18 OVERHEAD Fig 12-19 Overhead Fig 12-24 Overhead