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Topik 9
Muzik
1
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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.
4
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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).
5
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6
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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
7
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.
8
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
9
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.
11
A. B. C. D.
20
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.
12
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Bunyi atau Muzik?
Doc Cam - Figure 20.1
Wav Win - Noise and Wave Forms
Three characteristics of a musical tone:
13
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.
14
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15
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.
16
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Penggunaan gelombang bunyi
17
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.svg7/29/2019 Wk9 Sound Bm
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18
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.
19
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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?
20
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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
22
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.htm7/29/2019 Wk9 Sound Bm
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Review of Perception and Strings
The Guitar is a fretted stringed instrumentthat is plucked or strummed.
24
Neck
Body
Strings (6)
Tuning pegs
Bridge
Frets
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Review of Perception and Strings
80/20The coupling of the string to the soundboard will actuate or attenuate various
frequencies.
25
f1 f2 f3 f4fn
~ ~Sound Board and Acoustics filter
harmonics
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Review of Perception and Strings
80/20A Harp is a stringed instrument that isplucked. Its strings are of various lengths.
26
TraditionalIrish Harp
Strings
Sound Board
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Review of Perception and Strings
The principal pitch of each string in a PedalHarp is determined by its length.
27
Pedal Harp
However, depressing a pedal shortens or lengthens the string
length, raising (or lowering) the pitch incrementally.
Strings
Pedals
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Review of Perception and Strings
80/20A Harpsichord is a keyboard stringedinstrument whose strings are plucked.
Each string is used for one pitch only.
28
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Review of Perception and Strings
80/20A Harpsichord is a keyboard stringed instrument whosestrings are plucked.
Each string is used for one pitch only.
29
Key
JackString
PlectrumDamperarpsichordAction
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Review of Perception and Strings
80/20A Piano is a keyboard stringed instrumentwhose strings are hammered. Each string
is used for one pitch only.
30
Strings
Key Board
SoundBoard
Fortepiano Piano
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Review of Perception and Strings
80/20A Piano has multiple strings (in the treble)to provide a more powerful sound.
31
Multiple Strings
Sound Board Bridge Frame
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Review of Perception and Strings
Piano strings are tensioned by tuning pins in astrong frame.
32
Frame
Tuning Pins
Bass Strings
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Review of Perception and Strings
Piano hammers are made of felt and wood.
33
Pivot hinge
Hammer Head
Back CheckFelt
Wood
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Review of Perception and Strings
The timbre of the piano sound is affected bythe hardness of the hammer felt.
34
Felt
hard or soft?
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Review of Perception and Strings
80/20The timbre of a musical instrument isdetermined by the excitation, frequency
generation, filtering and broadcast of the
harmonics.
35
f1 f2 f3 f4fn
~ ~Excitationf Generation
f Response
Broadcast
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Review of Perception and Strings
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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Review of Perception and Strings
80/20The timbre of bowed strings is affected
by the properties of strings, by bowingand by the frequency resonances of the
instrument.
37
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Review of Perception and Strings
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)
38
Bow
Bridge
Strings
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Review of Perception and Strings
Pitch is changed by shortening the speakinglength of the strings by fingering
39
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Review of Perception and Strings
40
The strings are tensioned
by means of tuning pegs
in a scroll.
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Review of Perception and Strings
Density of strings sets range of each string
41
Denser wire: lower pitch
Less dense wire:
higher pitch
Viola Strings
Metal over catgut C3
G3
D4
A4
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Review of Perception and Strings
Different pitches can
be played on different
strings or on the same
string.
42
Example:Air on the G-String
J.S. Bach
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Review of Perception and Strings
Anatomy of a String
43
Guarneri Viola
Scroll
FingerboardBody
f Holes
Bridge
Tail piece
Stradivarius Violin
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Review of Perception and Strings
80/20The sound post transfers vibration fromfront plate to back plate and supports
bridge.
44
Sound postFront plate
Back plate
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Review of Perception and Strings
A rosined horse hair bow rubs the string.
45
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Review of Perception and Strings
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.
46
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Review of Perception and Strings
The Stick-Slip Mechanism causes the string tovibrate when rubbed by the bow.
47
Horse Hair
of Bow
StringSlip point
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Review of Perception and Strings
A complicated wave shoots down the stringwhen the string slips from the bow.
48
Moving Bow
Scroll Bridge
Waveform envelope
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Review of Perception and Strings
80/20The coupling of the string to the soundboard will accentuate or attenuate various
frequencies.
49
f1 f2 f3 f4fn
~ ~Sound Board and Acoustics filterharmonics
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Review of Perception and Strings
Cross Section of Violin
50
Scroll with
Tuning pegs
Finger board
Body
f-hole
Sound Post
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Review of Perception and Strings
Plates are of varying thickness and arehinged at edge (Purfling)
51
ThickerThinner
Purfling
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Review of Perception and Strings
The bridge is essential to transforming thelateral motion of the string into vibrations
of the top plate.
52
Bridge
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Review of Perception and Strings
Bridge Action
53
Sound
post
Bass
bar
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Review of Perception and Strings
Vibration is transmitted to the body and aircavity by the action of the Bridge.
54
Rocking
motion
HelmholtzResonance Sound post
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Review of Perception and Strings
Chladni plates simulate the vibrational modesof Violin Plates.
55
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Review of Perception and Strings
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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Review of Perception and Strings
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.
61
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).
62
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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.
63
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.jpg7/29/2019 Wk9 Sound Bm
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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.
64
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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.
65
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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.
66
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Hearing Loss
Hearing loss is caused by:
Injury
Infection Aging (like me?)
67
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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.
68
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Test
This Tuesday/Wednesday, March 3rd/4th.
Covers all of sound waves in chapter 16.