Transcript Sound - PAMS-Doyle

Sound
Chapter 21
How Sounds are Made
• Sounds are vibrations that
travel in longitudinal waves
• A vibration is the complete
back and forth motion of an
object
• At the crest of each wave is a
compression of the molecules
of the medium
• At the trough is a rarefaction
of the molecules of the
medium
Seeing Sound
Sound and Media
• Medium is the substance that the sound
wave travels through
• Fastest in solids, then liquids, then gases.
• Why?
• Space is a vacuum, with no matter to
carry the sound wave, so no sound is
heard from space.
How You Hear
• A is the pinna which collects the sound waves. It
is the beginning of the outer ear
• B is the ear canal which directs the sound waves
to the ear drum
• C is the ear drum which vibrates and sends the
vibrations into the middle ear
• D contains the hammer, anvil, and stirrup, which
are 3 small bones that vibrate and send the
vibrations to the inner ear
• E is the cochlea which is snail shaped and
contains a liquid and hundreds of nerves cells
which change the vibrations into nerve impulses
that are sent to the brain
» Threshold of Hearing
•
0dB
Normal Breathing
•
10dB
Rustling Leaves
•
20dB
•
30dB
•
40dB
•
50dB
•
60dB
•
70dB
Noisy Office with machines
•
80dB
Heavy Traffic
•
90dB
•
100dB
•
110dB
Library
Normal Conversation
Construction Noise (up close)
» Threshold of Pain
•
120dB
•
130dB
•
140dB
•
150dB
Rock Concert
Jet Takeoff (from runway)
Human Hearing
• Infrasonic – sounds 0-20 hz to low for
humans to hear
• Ultrasonic - sounds greater than 20,000
hz to high for humans to hear
• Most humans can hear 20-20,000 hz
most of their lives.
Hearing Loss and Deafness
• The most common type of hearing loss is called
tinnitus, caused by exposure to loud sounds or
music
•How to prevent it? Turn
your I-pods down!!!!!!
• Protect your hearing by wearing ear protectors if
you know you are going to be exposed to loud
noise.
Speed of Sound
• The speed of
sound is
determined by the
temperature,
elasticity, and
density of the
medium through
which the sound
travels
Temperature
• Sound travels faster at higher
temperatures and slower at lower
temperatures due to the molecules of
the medium
• Air at 0° 331 m/sec
• Air at 25° 346 m/sec
Elasticity and Density
• Solids are more elastic than either
liquids or gases, the medium returns
to its original position
ex. Running on pavement or sand
• Sound travels best in solids, then
liquids, and worst in gases because
the molecules are closer together in
solids
Frequency and Pitch
• The description of a sound as either high or low
is its pitch
• The pitch depends on the frequency of a sound
• High frequency=high pitch low frequency=low
pitch
• Ultrasonic higher than 20,000 hertz humans
cannot hear
• Unfrasonic lower that 20 hertz humans cannot
hear
Pitch
Doppler Effect
• The change in pitch due to the movement
between the sound and the receiver
• Coming toward the receiver the sound
waves are pushed together
• Moving away the sound waves have
more space between them
Intensity and Loudness
• Intensity determines the
loudness of a sound
• Intensity is the amount
of energy carried in a
wave in a certain
amount of time
• The larger the amplitude
the greater the intensity
of a wave
Reflection of Sound Waves
• Reflection of sound waves is called an echo
• Echolocation
Sonar
• High frequency ultra-sonic waves are
used in a system called Sound
Navigation And Ranging or sonar
Ultrasounds
•http://www.youtube.com/watch
?v=opCo2xZ9W8I&feature=rel
ated
• Ultrasonic waves are directed into a
body and the resulting picture can be
seen from the deflected waves
Combining Sounds
• When sound waves combine in such a way that
the resulting disturbance is greater then either
wave alone, constructive interference occurs
• When constructive interference occurs the
resulting sound gets louder
• Acoustics is the science of sound, acoustic
engineers design auditoriums to eliminate
interference problems
• Destructive interference
results when two sound
waves combine and the
resulting sound is less that
the two original sounds
• The sound gets softer
Constructive
Interference
Destructive
Interference
Sonic Boom
Standing Wave
• A pattern of vibration that looks like the
wave is standing still.
Resonance
• Natural vibration frequency
Beats
• Two waves of slightly different frequencies
overlap, adding together in some areas, canceling
each other in others. The bulges of loud sound
(high wave) are called beats.
Sound Quality
• Musical instruments have different sound quality
also known as timbre
• Each object vibrates at several different
frequencies, with different pitches, the blending
gives it its timbre
• The lowest is its fundamental tone and the highest
are overtones
• The blending of the fundamental tone and the
overtones produces the characteristic quality or
timbre of a particular sound
Music
• A sound is music if it has a pleasing
quality, a definite identifiable pitch, and a
repeating timing called rhythm
• Noise has no pleasing quality, no
identifiable pitch, and no definite
relationship between the fundamental
tone and the overtones
Heard enough?