SOUND CHAPTER 12. All Sound Has 3 Aspects… 1.Source 2.Energy 3.Detected Sound is Longitudinal...
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Transcript of SOUND CHAPTER 12. All Sound Has 3 Aspects… 1.Source 2.Energy 3.Detected Sound is Longitudinal...
SOUNDCHAPTER 12
All Sound Has 3 All Sound Has 3 Aspects…Aspects…
1.1. SourceSource2.2. EnergyEnergy
3.3. DetectedDetectedSound is Longitudinal Waves Sound is Longitudinal Waves (Compression Waves)(Compression Waves)Sound must have a medium.Sound must have a medium.Sound can’t travel in the absence Sound can’t travel in the absence of a mediumof a medium
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 ??
Table 12-1 Speed of Sound in various materials at 20°C
and 1atmMaterialMaterial Speed (m/s)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
LoudnessLoudness : Energy in a wave... Loosely : Energy in a wave... Loosely AmplitudeAmplitudePitch or FrequencyPitch or Frequency : # of Vibrations per : # of Vibrations per secondsecond
– High – FluteHigh – Flute– Low – TubaLow – Tuba
Humans can hear a range of frequenciesHumans can hear a range of frequencies• 20Hz to 20,000Hz – Humans20Hz to 20,000Hz – Humans• Above 20,000 Hz – Bats Above 20,000 Hz – Bats Ultra SonicUltra Sonic• Below 20Hz – Elephants Below 20Hz – Elephants Infra SonicInfra Sonic
Sound Intensity (B)Sound Intensity (B)
The unit for loudness is the The unit for loudness is the BelBel -- named -- named after Alexander Gram Bell. The unit was after Alexander Gram Bell. The unit was too big so we commonly refer to a 1/10 of too big so we commonly refer to a 1/10 of a bela beldB = decibeldB = decibelThe dB scale is logarithmic- it begins at 0 The dB scale is logarithmic- it begins at 0 – the quietest sound that can be heard– the quietest sound that can be heardDoubling sound intensity corresponds to Doubling sound intensity corresponds to an increase in dB of 3an increase in dB of 3
10x intensity gives an increase in dB 10x intensity gives an increase in dB of 10of 10100x intensity corresponds to dB 100x intensity corresponds to dB increase of 20increase of 20a 50 dB is 100 times more intense a 50 dB is 100 times more intense than a 30 dBthan a 30 dB
Pg. 351 has various sound levelsPg. 351 has various sound levelsspace shuttle 170dBspace shuttle 170dB
see chartsee chartTHE EAR see modelTHE EAR see model
Source of the soundSource of the sound
TABLE 12-2 Intensity of TABLE 12-2 Intensity of Various SoundsVarious Sounds
Intensity Level Intensity Level (dB)(dB)
Intensity Intensity W/mW/m22
Jet Plane at 30mJet Plane at 30m
Threshold of PainThreshold of Pain
Loud Indoor rock concertLoud Indoor rock concert
Siren at 30mSiren at 30m
Auto Interior, moving at 90km/hAuto Interior, moving at 90km/h
Busy Street TrafficBusy Street Traffic
Ordinary conversation, 50cmOrdinary conversation, 50cm
Quiet RadioQuiet Radio
WhisperWhisper
Rustle of LeavesRustle of Leaves
Threshold of hearingThreshold of hearing
140140
120120
120120
100100
7575
7070
6565
4040
2020
1010
00
100
1
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
Musical InstrumentMusical Instrument
Pitch is determined by the Pitch is determined by the lowest frequency. lowest frequency. (fundamental)(fundamental)
FF1=1= ½ ½λλ
FF2=2= λλ
FF3=3=3/23/2λλ
Overhead Picture- Overhead Picture- GuitarGuitar
•Changing the length of a Changing the length of a vibrating string (column of air) vibrating string (column of air) changes the frequency (Pitch)changes the frequency (Pitch)
•The velocity is the same on each The velocity is the same on each string so F is inversely string so F is inversely proportional to lengthproportional to length
Wind InstrumentsWind Instruments
TromboneTrombone
TrumpetTrumpet
TubaTuba
Pressing valves changes L of air Pressing valves changes L of air columncolumn
Bugle – no moving parts, Bugle – no moving parts, octave incrementsoctave increments
Sounding BoardSounding Board
Moving air in a column is a musical Moving air in a column is a musical instrument. The frequencies that instrument. The frequencies that persist are the ones that persist are the ones that correspond to standing wavescorrespond to standing waves
-Regarding Molecules of air-Regarding Molecules of air
Nodes represent NO motion of air Nodes represent NO motion of air molecules Antinodes represent the molecules Antinodes represent the most displacement.most displacement.
Tubes, Tubes, Open and ClosedOpen and Closed
OPENOPEN
FluteFlute
ClosedClosed
ClarinetClarinetWe can explain BOTH in terms of…
1. Displacement of air
2. Pressure
OVERHEADOVERHEAD
Figure 12-12 Figure 12-12 Standing waves in Standing waves in
open-open tubeopen-open tube
OverheadOverhead
Figure 12-13 Figure 12-13 Standing Waves Standing Waves in open-closed in open-closed
tubetube
Quality of SoundQuality of Sound
Quality of sound : timbre – tone Quality of sound : timbre – tone colorcolor
Quality is determined by overtonesQuality is determined by overtones
Quality happens by superposition Quality happens by superposition of wavesof waves
ConstructiveConstructive
DestructiveDestructive
Interference Interference
OscilloscopeOscilloscope
Sum of ALL THREE
1
22
33
Interference of Sound Waves 12-7Fig 12-17Fig 12-18
BeatsFig 12-19
Doppler EffectFig 12-20
Example probs:12-1312-14
Pg. 368Red ShiftShock Waves
Fig 12-24
Fig 12-20Fig 12-20
OVERHEADOVERHEAD
Fig 12-21
Fig 12-21 OverheadOverhead
Fig 12-17, 12-18
Fig 12-17, 12-18
OVERHEADOVERHEAD
Fig 12-19Fig 12-19OverheadOverhead
Fig 12-24Fig 12-24OverheadOverhead