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Transcript
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.
1
Compression
Rarefaction
Wavelength
2
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
3
1. Medium (solid, liquid or gas)
2. Temperature
4
5
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)
6
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?
7
All waves have 3 things in common.
1.
Frequency
2.
Pitch
3.
Intensity / Amplitude
8
. . .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
9
Doppler Effect
The sound changes to a
higher frequency when the
source comes towards
you...
...and to lower frequency
when it moves away
10
Depends on the frequency
Higher note / Higher frequency
Lower note / Lower frequency
White noise – equal mix of all frequencies
11
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.
12
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
13
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
14
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
15
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).
16
• 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
17
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)
18
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
19
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
20
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
21