Transcript PPT Sound 12

Sound
Sound waves travel through a medium and can be
visualized by Longitudinal or Compressional waves.
As the sound moves through the
medium, the particles vibrate against
one another causing the compressions:
A slinky is a good example of how
longitudinal waves behave.
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Compression
Rarefaction
Wavelength
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What is Sound?
• A sound wave is a pressure wave with
regions of high (compressions) and low
pressure (rarefactions) initiated by a
vibrating object.
• Combination of inertia and restoring
force produces harmonic motion and
waves
• Harmonic motion is an oscillation in
pressure and the wave is sound wave
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1. Medium (solid, liquid or gas)
2. Temperature
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Sound requires contact.
3350 m/s
Solid
1525 m/s
Liquid
343 m/s
Gas
So which of the above would be a better medium?
Sound does NOT travel in space –
there is no air to carry the sound (vacuum)
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Temperature
343 m/s 20°
322 m/s 0°
Do molecules move faster or slower as
temperature increases?
So would sound travel faster or slower
as temperature increases?
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All waves have 3 things in common.
1.
Frequency
2.
Pitch
3.
Intensity / Amplitude
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. . .the number of wave crests that pass one
place each second.
Frequency is measured in Hertz
A.
B.
Frequency and wavelength of sound are
inversely related – when frequency goes up the
wavelength goes down proportionally
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Doppler Effect
The sound changes to a
higher frequency when the
source comes towards
you...
...and to lower frequency
when it moves away
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Depends on the frequency
Higher note / Higher frequency
Lower note / Lower frequency
White noise – equal mix of all frequencies
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Which wave do you think has more intensity?
A.
B.
Intensity is defined as the amount
of energy (or amplitude) a wave has...
The greater intensity, the louder the sound will be.
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The measurement for intensity or loudness
is in DECIBELS (dB).
Here are some common sounds and their decibel ratings:
Near total silence - 0 dB
A whisper - 15 dB
Normal conversation - 60 dB
Lawnmower - 90 dB
A car horn - 110 dB
A rock concert or a jet engine - 120 dB
Gunshot, firecracker - 140 dB
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Ultrasonic • Frequency higher than 20,000Hz
• Used in Sonar and Medical Diagnosis and treatment.
Human Ear 20Hz to 20,000Hz
Best hearing between 100-2000 Hz
Infrasonic (subsonic) • Frequency lower than 20Hz
• Elephant Communication and Butterflies flapping
their wings, heavy machinery, thunder
Supersonic-
https://www.youtube.com/watch?v=gWGLAAYdbbc
• Motion that is faster than sound-do not hear
it until it passes you
• Example-supersonic jets make sonic boom
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Sonar • Sound Navigation Ranging
• Uses sound to estimate the size, shape and depth
of underwater objects.
• Examples: Submarines, whales and bats
• Sonogram-picture of a baby inside mom
Echo • Reflected sound waves
• Examples: Shouting in a cave or canyon
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How Loud is Loud?
• Any sound above 85 dB can cause hearing loss, and the
loss is related both to the intensity of the sound as well as
the length of exposure.
• You know that you are listening to an 85 dB sound if you
have to raise your voice to be heard by somebody else.
• For example, 8 hours of 90 dB sound can cause
damage, but any exposure to 140 dB sound causes
immediate damage (and causes actual pain).
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• Resonance
• prolonged vibrations of sound at their own natural
frequency.
• an opera singer can shatter a glass if the singer
resonates at the same frequency long enough
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SOUND in MUSIC
Acoustics = the science/study of sound
• Music has:
definite pitch
sound quality
repeating rhythm
• Types of Instruments:
Woodwinds(flute, clarinet)
Brass(horns)
Stringed(guitar, violin)
Percussion(drum, piano)
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Sound of Music
• rhythm – regular time pattern in a sound
• musical scale – set of frequencies (pitch)
• harmony – how sound works together to
create effects desired by the composer
• beats – adding two waves that are only
slightly different in frequencies
• noise-no set pattern and no definite pitch
• dead spots-areas where sound waves
cancel out
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Sound of Music
• consonance – more than one frequency
and it sounds good
– frequencies are far enough apart
• dissonance – more than one frequency
and it sounds bad
– frequencies are too close together
• quality-describes the differences among
sounds of the same pitch and loudness
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Sound of Music
• reverberation-many reflections of sound (echo)
• use of carpets, draperies to reduce reverberation
• interference-ability of two or more waves to
combine and form a new wave
1. constructive-different waves arrive at the
same place at the same time and cause an
increase in loudness
2. destructive-one wave will arrive with the
rarefaction of another wave and cancel each
other causing a decrease in loudness
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