Chapter 20Chapter 20
SoundSound
SlideSlide - A tree in the forest. - A tree in the forest.
1. ORIGIN OF SOUND1. ORIGIN OF SOUND
The frequency of a sound wave is The frequency of a sound wave is
the same as thethe same as the frequency of the frequency of the source of the sound wave.source of the sound wave.
Demo - Oscillator and speaker Demo - Oscillator and speaker Video – You Tube - Hearing Test – You Tube - Hearing Test
The human hearing range is aboutThe human hearing range is about
20 Hz - 20,000 Hz.
infrasonic.
Frequencies below 20 Hz are
Frequencies above 20,000 Hz areultrasonic.
2. NATURE OF SOUND IN AIR2. NATURE OF SOUND IN AIR
Video - Tuning ForkVideo - Tuning Fork
Demo - Strobed Tuning ForkDemo - Strobed Tuning Fork
Sound in air is longitudinal with Sound in air is longitudinal with
Compressions (Condensations)Compressions (Condensations)
andand
RarefactionsRarefactions
Demo - Vortex BoxDemo - Vortex Box
3. MEDIA THAT TRANSMIT SOUND3. MEDIA THAT TRANSMIT SOUND
Air is most common but is a poor Air is most common but is a poor
conductor.conductor.
Solids and liquids are good conductors.Solids and liquids are good conductors.
A medium is required.A medium is required.
Video - Vacuum PumpVideo - Vacuum Pump
4.4. SPEED OF SOUND IN AIRSPEED OF SOUND IN AIR Much slower than lightMuch slower than light Video – LumberjackVideo – Lumberjack
Thunder and LightningThunder and Lightning
ExplosionExplosion
Depends on wind, temperature, humidity
Slide - Wind and SnoopySlide - Wind and Snoopy Does not depend on frequency
Video – Sound DelayVideo – Sound Delay
At 0At 0o o C (dry air)C (dry air)
v = 1090 ft/sv = 1090 ft/s = 750 mi/hr = 330 m/s
increases with humidity
increases with
temperature
is faster in liquids and
solids
How v varies:
prolonging of sound by reflection
Rumble of distant thunder
(several reflections from
different distances)
5.5. REFLECTION OF SOUNDREFLECTION OF SOUND Occurs anytime waves change media. Occurs anytime waves change media.
Example: Echoes
Example:
Reverberation -
What is not reflected is transmitted What is not reflected is transmitted
and absorbed.and absorbed.
Examples: San Francisco Symphony Hall
Back of lecture room
The study of sound properties is acoustics.
6.6. REFRACTION OF SOUNDREFRACTION OF SOUND
When different parts of a wave front move at When different parts of a wave front move at
different speeds, the wave front will bend.different speeds, the wave front will bend.
This bending is known as refraction.This bending is known as refraction.
It occurs when different parts of a wave front are It occurs when different parts of a wave front are
traveling in different media.traveling in different media.
Slide - Sounds and Sleeping Dog Slide - Sounds and Sleeping Dog
Warm Air
Cool Air
Other ExamplesOther Examples
Thunder and lightningThunder and lightning
Sometimes distant lightning is not heard Sometimes distant lightning is not heard
well.well.
Other times it is.Other times it is.
Submarines and SonarRefraction due to thermal gradients can
“hide” submarines.
Ultrasound in medicineUltrasound echo and dolphins
7.7. ENERGY IN SOUND WAVESENERGY IN SOUND WAVES
Energy in sound is weak when compared Energy in sound is weak when compared
to the energy in light.to the energy in light.
The human ear is a remarkable detector.The human ear is a remarkable detector.
10 million people speaking at the same 10 million people speaking at the same
time produce approximately enough time produce approximately enough
energy to light one flashlight. energy to light one flashlight.
High frequencies of sound in air High frequencies of sound in air
more easily lose their energies to more easily lose their energies to
thermal energy than do low thermal energy than do low
frequencies.frequencies.That is why low frequencies can be heard farther away.
8.8. FORCED VIBRATIONSFORCED VIBRATIONS Demo - Tuning Fork Touching a TableDemo - Tuning Fork Touching a Table Sound is intensified because of the larger Sound is intensified because of the larger
surface area that can vibrate the air. surface area that can vibrate the air. The surface is forced to vibrate at the The surface is forced to vibrate at the
frequency of the tuning fork. (It is not a frequency of the tuning fork. (It is not a resonance phenomenon.)resonance phenomenon.)
Demo – Call Mobile Phone on TableDemo – Call Mobile Phone on Table
Examples: Musical sounding boards Examples: Musical sounding boards
9.9. NATURAL FREQUENCYNATURAL FREQUENCY Demo - Drop Different Sounding Demo - Drop Different Sounding
ObjectsObjects
Objects have natural frequencies at which they Objects have natural frequencies at which they
vibrate.vibrate.
The natural frequency depends on elasticity The natural frequency depends on elasticity
and shape.and shape.
Demo - Gravity ChimesDemo - Gravity Chimes
Demo – Boomwhackers Demo – Boomwhackers
Yankee Doodle
(arranged by Anthony T.)
Beethoven’s Ode to joy
Beethoven’s Ode to joy
(arranged by Anthony T.)
Christmas Boom WhackersChristmas Boom Whackers
Can Can BoomWhackersCan Can BoomWhackers
10.10. RESONANCE RESONANCE
Resonance occurs when successive Resonance occurs when successive impulses are applied to a vibrating impulses are applied to a vibrating object in time with its natural object in time with its natural frequency. frequency.
Result -Result - increased amplitudeExamples: Swinging
Marching on a bridge (rout step or break step)
Video - Matched Tuning ForksVideo - Matched Tuning Forks
Tuning Fork on GuitarTuning Fork on Guitar
Breaking GlassBreaking Glass
Demo - Matched Tuning ForksDemo - Matched Tuning Forks
Demo - Singing GlassDemo - Singing Glass
Glass armonica by Ben Franklin Glass armonica by Ben Franklin
Demo - Vibrating RodDemo - Vibrating Rod
Demo - Vibrating PlateDemo - Vibrating Plate
Demo - Fog HornDemo - Fog Horn
Submultiples of the naturalfrequency also produce resonance.
Demo - 256 & 512 Hz Tuning ForksDemo - 256 & 512 Hz Tuning Forks
Video - Tacoma Narrows Bridge (url)Video - Tacoma Narrows Bridge (url)
Note:
11.11.INTERFERENCEINTERFERENCE
Defined in Chapter 19Defined in Chapter 19
Demo - Oscillator & Two SpeakersDemo - Oscillator & Two Speakers
Slide - Oscillator & Two SpeakersSlide - Oscillator & Two Speakers
Examples:Examples:
Dead spots in theaters and music hallsDead spots in theaters and music halls
Anti-noise technologyAnti-noise technology
12. Beats12. Beats
Fluctuating loudness due to two tones of Fluctuating loudness due to two tones of slightly different frequencies that are slightly different frequencies that are sounded together (tremolo)sounded together (tremolo)
It is an interference effect.It is an interference effect. BeatsBeats//s = difference in frequenciess = difference in frequencies Musical instruments are tuned using Musical instruments are tuned using
beats.beats. Dolphins use beats and Doppler effect.Dolphins use beats and Doppler effect.
Slide - Beats Slide - Beats
Constructive Interference
Destructive Interference
Consider two waves of slightly different frequencies traveling together.
DC
URL - BeatsURL - Beats
Demo - Vibrating RodsDemo - Vibrating Rods
Demo - Two Oscillators & Two Demo - Two Oscillators & Two
SpeakersSpeakers
Demo - GuitarDemo - Guitar
RADIO BROADCASTSRADIO BROADCASTS
Slide - Radio BroadcastsSlide - Radio Broadcasts
AM -AM - 535 kHz to 1605 kHz
FM - 88 MHz to 108 MHz