wk9 sound bm

7/29/2019 Wk9 Sound Bm

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Topik 9

Muzik

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Bunyi

Gelombang

mekanikal yang

dihasilkan oleh

sesuatu yang

bergetar. Sejenis gelombang

membujur kerana

molekul-molekul

udara bergetar padaarah yang sama

dengan arah

perambatan bunyi.

Semasa getaran,satu siri mampatan &

renggangan

dihasilkan.


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Halaju Bunyi: 346 m/s pada suhu bilik.

Bunyi bergerak lebihcepat

(a) dalam bahantara

yang kenyal.

(b) dalam bahan yang

lebih tumpat.

(c) pada suhu yang

lebih tinggi.

Tidak boleh bergerak

melalui vakum.


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BUNYI Supersonik lebih cepat

daripada halaju bunyi.

Mach 2 dua kali lebihcepat daripada halajubunyi.

Subsonik lebihperlahan daripada halajubunyi.

Bergerak paling cepatdalam pepejal & palingperlahan dalam gas.

Halaju bunyi dalam keluli~17 kali lebih cepat

daripada dalam udara. Halaju bunyi dalam air

~4 kali lebih cepatdaripada dalam udara.

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BUNYI Had frekuensi pendengaran manusia ialah antara

20 Hz ke 20 000 Hz. Halaju bunyi, v = f di mana = jarak gelombang

Bunyi boleh menghasilkan fenomena

(a) pantulan (gema),

(b) pembiasan (belon CO2 yang telah tumpat

bertindak macam kanta cembung untuk

menumpu bunyi),

(c) pembelauan (bunyi didengar pada sudutdinding) &

(d) interferens (bunyi kuat & lemah dalam bilik

apabila terdapat 2 pembesar suara).

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Keamatan (Intensity) atau kenyaringan

Keamatan bunyi,Iadalah jumlahtenaga, E yangdibawa gelombangper saat (t) melalui1 m2 luas, L.

I = E/Lt

Bunyi yang

mempunyaikeamatan yangtinggi biasanyalebih kuat!

2AI

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Keamatan bunyiadalah berkadar

terus dengan kuasadua amplitudgelombang.


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Kekuatan Bunyi

Kekuatan bunyi diukurdalam unit decibels

(dB).

Tahap pendengaran

ialah pada 0 decibels. Kekuatan bunyi lebih

kuat daripada 120

decibels boleh

menyebabkan

kesakitan &

kerosakan telinga.

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Rumus untuk decibel:

Tahap terendahpendengaran,

I0

= 10-12 W/m2 atau 0 dB

Tahap permulaan sakitpendengaran = 1 W/m2 atau120 dB

0

log10I

IdB


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Keamatan & Kekuatan Bunyi-Bunyi Biasa

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Source of Sound Intensity, I (W/m2) Sound Level, (db)

Threshold of Hearing I0 = 10-12 0

10

20

40

60

70110

120

140

10-11

10-10

10-8

10-6

10-5

10-1

1

102

Rustle of Leaves

Whisper

Quiet Radio in Home

Conversation in Home

Busy Street TrafficDisco Music Amplified

Air-raid Siren, Nearby

Jet, 30 m Away


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Frekuensi & Kelangsingan (Pitch) Bunyi yang lebih tinggi

frekuensinya mempunyai

kelangsingan lebih tinggi.

Julat frekuensi

pendengaran manusia

ialah antara 20 Hz dan

20,000 Hz.

Ultrasonik gelombang

bunyi yang berfrekuensi

melebihi had

pendengaran manusia.

Infrasonik gelombang

bunyi yang berfrekuensi

kurang daripada had

pendengaran manusia. 10

Frekuensi = bil. getaran/saat

f tinggi lebih getaran sesaat


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Bila frekuensi gelombang bunyi bertambah, . . . .

A. Kelangsingan bertambah.

B. Kelangsingan berkurang.C. Kelangsingan tidak berubah.

D. Kelangsingan bertambah dan

kemudiannya berkurang.

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A. B. C. D.

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21

0


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Resonan Resonan berlaku apabila frekuensi gelombang bunyi

sama dengan frekuensi semula jadi (naturalfrequency) objek yang bergetar.

Jika resonan berlaku pada objek bergetar yang tidak

fleksibel atau tegar seperti gelas, jambatan dll, objek

tersebut boleh pecah.

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Bunyi atau Muzik?

Doc Cam - Figure 20.1

Wav Win - Noise and Wave Forms

Three characteristics of a musical tone:

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Kelangsingan?

Kekuatan?

Kualiti?


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Muzik

Suatu nada muzik ialah suatu bunyi yang

mempunyai frekuensi yang teratur.

Jenis-jenis instrumen muzik:

Strings

Brass

Woodwinds

Percussion

Cth: Tali gitar yang dipetik dengan lebih kuat (amplitudlebih besar) akan menghasilkan kenyaringan bunyi

yang lebih tinggi.

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Nada muzik menentukan kualiti muzik. Nada muzikyang dihasilkan alat-alat muzik berlainan akan

mempunyai bentuk gelombang berlainan. Ini

disebabkan setiap alat muzik menghasilkan

frekuensi asas & nada yang berlainan.

Nada Muzik (Timbre) Setiap Alat Muzik


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A Guitar is a stringed instruments with fretsplayed by plucking.

A Harp is a fretless stringed instrument playedby plucking.

The Harpsichord is a stringed instrument withkeys which when depressed lift a plectrumthat plucks one or more strings.

The Piano is a stringed instrument with akeyboard which causes a felt hammer tostrike the string.

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Penggunaan gelombang bunyi

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Sonar- Untuk menentukan kedalaman

laut. Pemancar ultrasonik yang

dipasang di bahagian bawah kapal

memancar denyutan ultrasonik ke

dasar laut. Pantulan bunyi atau gema

diterima mikrofon pada kapal.

Sonar- Untuk menyiasat keadaan organ

pesakit atau keadaan bayi dalam

kandungan ibu. Pemancar ultrasonikmemancardenyutan ultrasonik

menghala bayi. Pantulan bunyi atau

gema diterima alat penerima yang

diterjemah komputer.
http://www.answers.com/main/Record2?a=NR&url=http%3A%2F%2Fcommons.wikimedia.org%2Fwiki%2FImage%3ASonar%2520Principle%2520EN.svg


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Sonar- Untuk mengesan retakan atau

kecacatan dalam struktur logam.

Bahagian tertentu sesuatu pesawat,landasan kereta api, atau paip logam

boleh diuji tanpa merosakkan

strukturnya. Sonar- Untuk membantu nelayan

mengesan kedudukan kumpulan ikan

dalam laut. Sonar- Untuk membantu ahli geologi

mengesan kedudukan simpanan

minyak dalam kerak bumi.


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Facts: More than 40 million Americans have hearing

loss. Approximately 40% of the hearing-impaired are

under age 65.

About 2 million children under age 18 are

hearing-impaired in the U.S. Some form of hearing loss affects 1 out of 5

people by age 55.

About 15% of college graduates have a level ofhearing loss equal to or greater than theirparents; a significant cause is listening to loudmusic.

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Review Questions1. What type of wave is sound?

2. What are three factors that affect the speed of sound?3. What are the three bones in the middle ear?

4. Is sound faster in warmer or cooler temperatures?

5. Is sound faster in elastic material or material that is notelastic?

6. Is sound faster in less dense or more dense medium?

7. What does the stirrup shake in the middle ear?

8. What does sonar stand for?

9. How do bats navigate?

10. What is the property of sound that is described as the

amount of energy that passes by a point each second?

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Review Questions11. Sound is measured in ________________.

12. Sound waves with frequencies below the human range ofhearing is known as _______________.

13. Sound waves with frequencies above the human range of

hearing is known as _______________.

14. When the frequency of an object and the natural frequency

are the same, it is known as _______________.

15. _______________ describes the quality of sound.

16. Sound with no identifiable pitch and unpleasing to the ear

is known as _______________.

17. Sound pleasing to the ear with an identifiable pitch is

known as _______________. 21


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ISL

Gather and document the information on

a) Temperature scales: Celsius and Kelvin

b) Different types of thermometers and also on

c) How to build a simple telescope and microscope.

Write a summary of your understanding in the

reflective log.

http://inventors.about.com/library/inventors/blthermometer.htm

http://en.wikipedia.org/wiki/Telescope

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http://inventors.about.com/library/inventors/blthermometer.htmhttp://inventors.about.com/library/inventors/blthermometer.htmhttp://en.wikipedia.org/wiki/Telescopehttp://en.wikipedia.org/wiki/Telescopehttp://inventors.about.com/library/inventors/blthermometer.htmhttp://inventors.about.com/library/inventors/blthermometer.htm


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Review of Perception and Strings

The Guitar is a fretted stringed instrumentthat is plucked or strummed.

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Neck

Body

Strings (6)

Tuning pegs

Bridge

Frets


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80/20The coupling of the string to the soundboard will actuate or attenuate various

frequencies.

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f1 f2 f3 f4fn

~ ~Sound Board and Acoustics filter

harmonics


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80/20A Harp is a stringed instrument that isplucked. Its strings are of various lengths.

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TraditionalIrish Harp

Strings

Sound Board


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The principal pitch of each string in a PedalHarp is determined by its length.

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Pedal Harp

However, depressing a pedal shortens or lengthens the string

length, raising (or lowering) the pitch incrementally.

Strings

Pedals


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80/20A Harpsichord is a keyboard stringedinstrument whose strings are plucked.

Each string is used for one pitch only.

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80/20A Harpsichord is a keyboard stringed instrument whosestrings are plucked.

Each string is used for one pitch only.

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Key

JackString

PlectrumDamperarpsichordAction


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80/20A Piano is a keyboard stringed instrumentwhose strings are hammered. Each string

is used for one pitch only.

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Strings

Key Board

SoundBoard

Fortepiano Piano


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80/20A Piano has multiple strings (in the treble)to provide a more powerful sound.

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Multiple Strings

Sound Board Bridge Frame


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Piano strings are tensioned by tuning pins in astrong frame.

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Frame

Tuning Pins

Bass Strings


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Piano hammers are made of felt and wood.

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Pivot hinge

Hammer Head

Back CheckFelt

Wood


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The timbre of the piano sound is affected bythe hardness of the hammer felt.

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Felt

hard or soft?


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80/20The timbre of a musical instrument isdetermined by the excitation, frequency

generation, filtering and broadcast of the

harmonics.

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f1 f2 f3 f4fn

~ ~Excitationf Generation

f Response

Broadcast


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Summary (strings): fn = [n/(2L)] (T/ )

The node-antinode distance is .

The timbre of a stringed instrument isdetermined by its harmonic recipe.

The harmonic recipe of a stringed instrument isdetermined by its mode of excitation, theharmonics of a string, and the natural

frequency response of the instrument.36


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80/20The timbre of bowed strings is affected

by the properties of strings, by bowingand by the frequency resonances of the

instrument.

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Bowed String Instruments Violin

G3, D4, A4, E5 (5ths)

Viola C3, G3, D4, A4(5th below violin)

Cello C2, G2, D3, A3

(8vo below viola)

Bass (Viol) E2, A2, D3, G3 (4ths)

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Bow

Bridge

Strings


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Pitch is changed by shortening the speakinglength of the strings by fingering

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The strings are tensioned

by means of tuning pegs

in a scroll.


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Density of strings sets range of each string

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Denser wire: lower pitch

Less dense wire:

higher pitch

Viola Strings

Metal over catgut C3

G3

D4

A4


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Different pitches can

be played on different

strings or on the same

string.

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Example:Air on the G-String

J.S. Bach


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Anatomy of a String

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Guarneri Viola

Scroll

FingerboardBody

f Holes

Bridge

Tail piece

Stradivarius Violin


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80/20The sound post transfers vibration fromfront plate to back plate and supports

bridge.

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Sound postFront plate

Back plate


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A rosined horse hair bow rubs the string.

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The Action of the Bow

The rubbing of the bow

alternately pulls the string

forward, then releases

it when the string wave

reaches the bow.

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The Stick-Slip Mechanism causes the string tovibrate when rubbed by the bow.

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Horse Hair

of Bow

StringSlip point


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A complicated wave shoots down the stringwhen the string slips from the bow.

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Moving Bow

Scroll Bridge

Waveform envelope


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80/20The coupling of the string to the soundboard will accentuate or attenuate various

frequencies.

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f1 f2 f3 f4fn

~ ~Sound Board and Acoustics filterharmonics


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Cross Section of Violin

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Scroll with

Tuning pegs

Finger board

Body

f-hole

Sound Post


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Plates are of varying thickness and arehinged at edge (Purfling)

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ThickerThinner

Purfling


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The bridge is essential to transforming thelateral motion of the string into vibrations

of the top plate.

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Bridge


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Bridge Action

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Sound

post

Bass

bar


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Vibration is transmitted to the body and aircavity by the action of the Bridge.

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Rocking

motion

HelmholtzResonance Sound post


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Chladni plates simulate the vibrational modesof Violin Plates.

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Summary (Bowed Strings): fn = [n/(2L)] (T/ )

The bow works by the Slip-slick mechanism.

The timbre of a bowed stringed instrumentis determined by its harmonic recipe.

The harmonic recipe of a bowed stringedinstrument is determined by its modes ofexcitation, the harmonics of a string, and

the natural frequency response of the 56


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Summary: A violin, viola, cello and bass are stringed

instruments with a finger board played bybowing.

The string vibrates the bridge which

vibrates the top plate.

The sound post transmits the vibration tothe back plate.

The timbre of the violin family is stronglyaffected by the modes of vibration of theinstrument. 57


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The Doppler Effect

The apparent change infrequency as a wave sourcemoves in relation to the

listener is called the DopplerEffect.

As sound source moves towardthe listener, the waves reachthe listener with a higherfrequency.

The pitch appears to increasebecause of the Doppler effect.

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SOUND AND MUSIC


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SOUND AND MUSIC

f= f(v + vd)/(v vs)

The Doppler effect explains why

objects moving toward or away

from each other sounddifferent than when they are

standing still.

f is the measured frequency by

the detector,fis the frequencyemitted by the source.

vis the speed of sound, vd is the

velocity of the detector, and vs

is the velocity of the source. If the objects are approaching

each other, use the top sign

(+vd, -vs).

If the objects are receding fromeach other, use the bottom sign

(-vd, +vs).

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Hearing Sound

The outer ear funnels

sound waves, the middle

ear transmits the wavesinward, and the inner ear

converts the sound waves

into a form that your

brain can understand.

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http://hyperphysics.phy-astr.gsu.edu/hbase/sound/ear.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/sound/ear.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/sound/oss.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/sound/cochlea.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/sound/ear.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/sound/ear.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/sound/ear.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/sound/ear2.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/sound/ear.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/sound/ear2.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/sound/ear.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/sound/ear.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/sound/ear.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/sound/ear.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/sound/oss.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/sound/oss.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/sound/oss.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/sound/eari.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/sound/eari.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/sound/cochlea.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/sound/cochlea.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/sound/anerv.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/sound/ear2.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/sound/ear2.htmlhttp://en.wikipedia.org/wiki/Image:HumanEar.jpg


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Outer Ear

The outer ear funnels the

sound waves to the ear

canal. The sound travels down

the ear canal and vibrates

the eardrum.

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Middle Ear

The middle ear contains

three small bones:

hammer, anvil andstirrup.

The vibrations travel from

the eardrum to the

hammer, then the anviland finally the stirrup.

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Inner Ear

The stirrup vibrates the

cochlea.

The cochlea contains fluidand tiny hairs that are

stimulated by the

vibrations.

The stimulations of thetiny hairs send messages

to the brain.

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Hearing Loss

Hearing loss is caused by:

Injury

Infection Aging (like me?)

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Facts:

In the U.S., 12 million people have hearing aids.

Of the 12 million with hearing aids, only 6 million actually

wear them eight hours a day, seven days a week.

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Test

This Tuesday/Wednesday, March 3rd/4th.

Covers all of sound waves in chapter 16.

wk9 sound bm

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