Sound

Chapter 21Chapter 21

How Sounds are Made• Sounds are vibrations that Sounds are vibrations that

travel in longitudinal wavestravel in longitudinal waves

• A vibration is the complete back A vibration is the complete back and forth motion of an objectand forth motion of an object

• At the crest of each wave is a At the crest of each wave is a compression of the molecules compression of the molecules of the mediumof the medium

• At the trough is a rarefaction of At the trough is a rarefaction of the molecules of the mediumthe molecules of the medium

Seeing Sound

Sound and Media• Medium is the substance that the sound Medium is the substance that the sound

wave travels throughwave travels through

• Fastest in solids, then liquids, then gases.Fastest in solids, then liquids, then gases.

• Why?Why?

• Space is a vacuum, with no matter to Space is a vacuum, with no matter to carry the sound wave, so no sound is carry the sound wave, so no sound is heard from space.heard from space.

How You Hear

• A is the pinna which collects the sound waves. It A is the pinna which collects the sound waves. It is the beginning of is the beginning of the outer earthe outer ear

• B is the ear canal which directs the sound waves B is the ear canal which directs the sound waves to the ear drumto the ear drum

• C is the ear drum which vibrates and sends the C is the ear drum which vibrates and sends the vibrations into the vibrations into the middle earmiddle ear

• D contains the hammer, anvil, and stirrup, which D contains the hammer, anvil, and stirrup, which are 3 small bones that vibrate and send the are 3 small bones that vibrate and send the vibrations to the vibrations to the inner earinner ear

• E is the cochlea which is snail shaped and E is the cochlea which is snail shaped and contains a liquid and hundreds of nerves cells contains a liquid and hundreds of nerves cells which change the vibrations into nerve impulses which change the vibrations into nerve impulses that are sent to the brainthat are sent to the brain

» Threshold of HearingThreshold of Hearing• 0dB 0dB Normal BreathingNormal Breathing

• 10dB 10dB Rustling LeavesRustling Leaves

• 20dB20dB

• 30dB 30dB Library Library

• 40dB40dB

• 50dB50dB Normal ConversationNormal Conversation

• 60dB60dB

• 70dB70dB Noisy Office with machines Noisy Office with machines

• 80dB80dB Heavy TrafficHeavy Traffic

• 90dB90dB

• 100dB100dB Construction Noise (up close)Construction Noise (up close)

• 110dB110dB» Threshold of PainThreshold of Pain

• 120dB120dB Rock Concert Rock Concert

• 130dB130dB

• 140dB140dB Jet Takeoff (from runway)Jet Takeoff (from runway)

• 150dB150dB

Human Hearing

• InfrasonicInfrasonic – sounds 0-20 hz to low for – sounds 0-20 hz to low for humans to hearhumans to hear

• UltrasonicUltrasonic - sounds greater than 20,000 - sounds greater than 20,000 hz to high for humans to hearhz to high for humans to hear

• Most humans can hear 20-20,000 hz Most humans can hear 20-20,000 hz most of their lives.most of their lives.

Hearing Loss and Deafness• The most common type of hearing loss is called The most common type of hearing loss is called

tinnitus, tinnitus, caused by exposure to loud sounds or caused by exposure to loud sounds or musicmusic

• How to prevent it? Turn How to prevent it? Turn your I-pods down!!!!!!your I-pods down!!!!!!

• Protect your hearing by wearing ear protectors if Protect your hearing by wearing ear protectors if you know you are going to be exposed to loud you know you are going to be exposed to loud noise.noise.

Speed of Sound• The speed of sound The speed of sound

is determined by is determined by the temperature, the temperature, elasticity, and elasticity, and density of the density of the medium through medium through which the sound which the sound travelstravels

Temperature• Sound travels faster at higher Sound travels faster at higher

temperatures and slower at lower temperatures and slower at lower temperatures due to the molecules of temperatures due to the molecules of the mediumthe medium

• Air at 0Air at 0° 331 m/sec° 331 m/sec

• Air at 25° 346 m/secAir at 25° 346 m/sec

Elasticity and Density• Solids are more elastic than either Solids are more elastic than either

liquids or gases, the medium returns to liquids or gases, the medium returns to its original position its original position ex. Running on pavement or ex. Running on pavement or sandsand

• Sound travels best in solids, then Sound travels best in solids, then liquids, and worst in gases because the liquids, and worst in gases because the molecules are closer together in solidsmolecules are closer together in solids

Frequency and Pitch• The description of a sound as either high or low The description of a sound as either high or low

is its pitchis its pitch

• The pitch depends on the frequency of a soundThe pitch depends on the frequency of a sound

• High frequency=high pitch low frequency=low High frequency=high pitch low frequency=low pitchpitch

• Ultrasonic higher than 20,000 hertz humans Ultrasonic higher than 20,000 hertz humans cannot hearcannot hear

• Unfrasonic lower that 20 hertz humans cannot Unfrasonic lower that 20 hertz humans cannot hearhear

Pitch

Doppler Effect

• The change in pitch due to the movement The change in pitch due to the movement between the sound and the receiverbetween the sound and the receiver

• Coming toward the receiver the sound Coming toward the receiver the sound waves are pushed togetherwaves are pushed together

• Moving away the sound waves have Moving away the sound waves have more space between them more space between them

Intensity and Loudness• Intensity determines the Intensity determines the

loudness of a soundloudness of a sound

• Intensity is the amount Intensity is the amount of energy carried in a of energy carried in a wave in a certain wave in a certain amount of timeamount of time

• The larger the amplitude The larger the amplitude the greater the intensity the greater the intensity of a waveof a wave

Reflection of Sound Waves• Reflection of sound waves is called an echoReflection of sound waves is called an echo

• EcholocationEcholocation

Sonar• High frequency ultra-sonic waves are High frequency ultra-sonic waves are

used in a system called used in a system called SoSound und NNavigation avigation AAnd nd RRanging or sonaranging or sonar

Ultrasounds• Ultrasonic waves are directed into a Ultrasonic waves are directed into a

body and the resulting picture can be body and the resulting picture can be seen from the deflected wavesseen from the deflected waves

•http://www.youtube.com/watch?v=opCo2xZ9W8I&feature=related

Combining Sounds

• When sound waves combine in such a way that When sound waves combine in such a way that the resulting disturbance is greater then either the resulting disturbance is greater then either wave alone, constructive interference occurswave alone, constructive interference occurs

• When constructive interference occurs the When constructive interference occurs the resulting sound gets louderresulting sound gets louder

• Acoustics is the science of sound, acoustic Acoustics is the science of sound, acoustic engineers design auditoriums to eliminate engineers design auditoriums to eliminate interference problemsinterference problems

• Destructive interference Destructive interference results when two sound results when two sound waves combine and the waves combine and the resulting sound is less that resulting sound is less that the two original soundsthe two original sounds

• The sound gets softerThe sound gets softer

Constructive DestructiveConstructive Destructive

InterferenceInterference Interference Interference

Sonic Boom

Standing Wave• A pattern of vibration that looks like the A pattern of vibration that looks like the

wave is standing still.wave is standing still.

Resonance• Natural vibration frequencyNatural vibration frequency

Beats• Two waves of slightly different frequencies Two waves of slightly different frequencies

overlap, adding together in some areas, canceling overlap, adding together in some areas, canceling each other in others. The bulges of loud sound each other in others. The bulges of loud sound (high wave) are called (high wave) are called beats.beats.

Sound Quality• Musical instruments have different sound quality Musical instruments have different sound quality

also known as timbrealso known as timbre

• Each object vibrates at several different Each object vibrates at several different frequencies, with different pitches, the blending frequencies, with different pitches, the blending gives it its timbregives it its timbre

• The lowest is its fundamental tone and the highest The lowest is its fundamental tone and the highest are overtonesare overtones

• The blending of the fundamental tone and the The blending of the fundamental tone and the overtones produces the characteristic quality or overtones produces the characteristic quality or timbre of a particular soundtimbre of a particular sound

Music

• A sound is music if it has a pleasing A sound is music if it has a pleasing quality, a definite identifiable pitch, and a quality, a definite identifiable pitch, and a repeating timing called rhythmrepeating timing called rhythm

• Noise has no pleasing quality, no Noise has no pleasing quality, no identifiable pitch, and no definite identifiable pitch, and no definite relationship between the fundamental relationship between the fundamental tone and the overtonestone and the overtones

Heard enough?