Upcoming Classes

1
Upcoming Classes

• Tuesday, Oct. 30th
• Music at the Nexus
• Special Guest Prof. Brian Holmes, Composer and
  French Horn player
• Assignment due None, BUT attendance counts
  as two quizzes
• Thursday, Nov. 1st
• Radio and Television (and Microwaves and X-rays)
  
• Assignment due
• Read Electromagnetic Radiation, Seeing the
  Light Optics in Nature, Photography, Color,
  Vision, and Holography, D. Falk, D. Brill, D.
  Stork, Pages 16-25

2
Brian Holmes, Composer

• Professor Brian Holmes is a composer and
  professional French Horn player. He also has a
  Ph.D. in Physics and teaches in both the Music
  and Physics departments at SJSU.

3
Extra Credit Concert at Petit Trianon

• See the premier performance of Brian Holmes
  Death's Jest-Book Overture by the Mission Chamber
  Orchestra on Sat., Nov. 3rd, 730pm.
• Turn in your ticket receipt (student tickets are
  17). Worth two quiz/participation credits.

Le Petit Trianon, 72 N. 5th St., San Jose
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Extra Credit Beethoven Center

• Visit the Beethoven Center on the Fifth floor of
  MLK library.
• Take a photo of yourself with one of the pianos
  or harpsichords.
• Turn in photo by Thurs., Nov. 11th for one quiz
  worth of extra credit.

5
Homework Exploratorium

• Located near Golden Gate Bridge.

6
Upcoming Deadlines

• Tuesday, October 16th
• Outline of second oral presentation or written
  paper
• Tuesday, November 6th
• Second Set of Oral Presentations
• Second term paper (if not presenting)

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Oral Presentations (II)

• The following persons will give oral
  presentations on Tuesday, November 6th
• Luttrell,Katherine
• Macdonald,Keith
• McDonald,Kathleen
• Mendoza,Jazmin
• Nguyen,Jennifer
• Nguyen,Linda
• For everyone else, term paper is due on that
  date.

8
Extra Credit San Jose Ballet

• See a performance of San Jose Ballet in San Jose
  Center for Performing Arts (Nov. 15th 18th ).
• Turn in your ticket receipt. Worth one homework
  assignment or three quiz/participation credits.

Ramon Moreno in CARMINA BURANA
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Instruments Musical and Scientific
10
Hearing Making Music

• This lecture we finish the discussion on hearing
  music and consider details of how to make it.

11
Loudness Amplitude

• Loudness depends on amplitude of pressure and
  density variations in sound waves.

12
Decibels
Loudness is measured in decibels (dB), which is a
logarithmic scale (since our perception of
loudness varies logarithmically). From the
threshold of hearing (0 dB) to the threshold of
pain (120 dB) the pressure increase is a million
times higher. At the threshold of pain (120 db)
the pressure variation is only about 10 Pascals,
which is one ten thousandths atmospheric pressure.
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Demo Make Some Noise

• Lets experience the loudness of sound like by
  clapping at various decibel levels.

Sound Meter
Start clapping softly and slowly increase or
decrease loudness, as I direct you using the
sound meter.
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Amplitude Frequency
Perceived loudness contours for various
frequencies and amplitudes
Low frequency and very high frequency sound
requires high amplitude to be heard
15
Hearing by Age Sex
Hearing acuity decreases with age, especially in
the high frequencies. In general, women have
greater acoustic sensitivity than men.
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Hearing Loss
The hair cells that line the cochlea are a
delicate and vulnerable part of the ear. Repeated
or sustained exposure to loud noise destroys the
neurons of the Organ of Corti. Once destroyed,
the hair cells are not replaced, and the sound
frequencies interpreted by them are no longer
heard.

• Hair cells that respond to high frequency sound
  are very vulnerable to destruction, and loss of
  these neurons typically produces difficulty
  understanding human voices.
• Much of this type of permanent hearing loss is
  avoidable by reducing exposure, such as to loud
  music.

What?
17
Musical Instruments
Now that we understand more about the physics of
sound, lets analyze how it is produced by
different types of musical instruments.
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Brass Instruments
Resonant standing waves produced in a pipe
(horn) the set of frequencies (notes) depends on
the length of the pipe.
Brass instruments (trumpets, trombones, horns,
etc.) are loud since they very efficiently
generate sound and so only a few are needed in an
orchestra.
Valves used to vary the length through in pipe
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Woodwind Instruments
Resonant standing waves also produced in a pipe
but the pipe length varied by air holes
(finger-holes, keys, or pads).
Flute
Oboe
Cor anglais
Saxophone
Clarinet
Bassoon
Meter stick
20
Brass Woodwind Vibrations

• Vibrations in a pipe created by
• Vibrating ones lips (e.g., trumpet)
• Blowing past an opening (e.g., flute)
• Blowing vibrating a reed (e.g., clarinet)

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Demo Playing a Straw

• Can make a simple reed by cutting a straw, as
  shown, lightly placing it between your lips, and
  blowing hard.

What happens if you shorten the straw (e.g., cut
it in half)?
22
Recorder Pipe Organ

• Oscillations in a pipe induced by pushing air
  through the pipe.

Different length pipes for different notes
Recorder has finger-holes
23
Demo Hoot Tubes

• Large tube has a metal screen near one end.
• Heat screen with a flame.
• Remove tube from the flame and it plays like an
  organ pipe.

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Hoot Tubes, Analyzed

• Remove the flame and hot air rises from the
  screen, drawing in cold air.
• Hot air rising through pipe causes vibration at
  natural frequency, which depends on the length of
  the pipe.

FLAME
25
Vibrations in Woodwinds

• What exactly creates the oscillations when we
  blow into a woodwind instrument?

The Oboe Player, Thomas Eakins, 1903   
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Bernoullis Principle

• Where the speed of a fluid increases the pressure
  in the fluid decreases.
• This phenomenon is due to energy conservation
  when fluids kinetic energy increases (velocity
  increases) its internal potential energy
  (pressure) decreases.

Still Air
A
Wind
L
27
Demo Blow It Up

• Hold a sheet of paper in front of your mouth and
  blow the paper will rise.

L
A
28
Check Yourself

• Wind blowing over the ocean causes waves to build
  due to Bernoullis principle.
• Where is the pressure lowered?

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Blow the Roof
If wind blows hard enough the low pressure above
can create a large enough force to lift the roof
off.
L
A
New Orleans Superdome after hurricane Katrina
30
Demo Blow It Off

• Bend cardboard into a U-shape. Place on table,
  legs down, and try to blow it off.

Fast moving air in the channel between the card
and the table creates a low pressure region,
pressing the card downward.
Front view
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Demo Blow the Funnel
BLOW

• Blow hard through a funnel with a ping pong ball
  in the funnels bowl.
• Instead of being blown away, the ball is held
  tightly in the bowl.

Ping Pong Ball
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Airplane Wing

• Pressure difference created by Bernoulli effect
  creates upward lift.

LIFT FORCE
L
Wing
A
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Demo Keep It Up

• Objects in a moving steam of fluid are pulled to
  the center of the stream because pressure is
  lower inside the stream than outside.

34
Demo Whirly Tube

• Whirl a corrugated tube to produce a pure tone at
  the tubes natural frequency.
• Bernoulli principle creates low pressure at the
  moving end, drawing air through the tube.

L
A
35
Whistling

• Pressure difference between moving and stationary
  air creates oscillating vortices.

Wire
Hole Whistling
L
A
A
L
L
Air
Air
A
Whistling wires
36
Percussion Instruments

• Create oscillations by striking an object, such
  as
• Stretched drumhead
• Metal rod or disk
• Wooden object
• Stretched string

37
Evolution of the Piano
Dulcimer
Clavichord
Piano Hammer
Harpsichord
Visit the Beethoven Center on the fifth floor of
MLK library.
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String Instruments
Standing wave on the vibrating string causes
forced oscillation of the sounding board.

• Frequency for a string depends on
• Length of string
• Thickness and composition
• Tension in the string

Modern piano has many long, massive steel strings
under high tension (hundreds of pounds) on a
large sounding board.

• Loudness depends on
• Amplitude of oscillation
• Mass of the string
• Frequency

39
Drum Heads

• Drum heads are stretched membranes that vibrate
  at different frequencies depending on the
  membranes oscillation pattern.

Note These animations are not accurate because
complex patterns should oscillate faster.
40
Loudspeakers
Loudspeaker has a membrane but oscillations are
created by variations in electrical current,
which cause an electromagnet to be pulled towards
and away from a second, permanent magnet.
These oscillations cause the membrane of the
loudspeaker to vibrate with the same frequency as
the oscillations in the electrical current.
Headphones work essentially the same way, theyre
just smaller.
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Constructive Interference

• Two waves in phase add together, which is called
  constructive interference.

42
Destructive Interference

• Two waves out of phase cancel each other out,
  which is destructive interference.

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In Out of Phase
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Demo In Out of Phase

• Pair of speakers constructively interfere when
  they are in phase (oscillating together).
• When out of phase (reverse wires on one of the
  speakers) then they destructively interfere.

Out of Phase
45
Noise-Canceling Headphones

• Noise-canceling headphones use a microphone that
  listens for noise and a speaker that produces the
  same noise but out of phase (cancellation by
  destructive interference)

External Noise
Canceling Sound
46
Demo Speaker Baffle

• Why are speakers mounted behind a baffle and
  inside an enclosure?
• To minimize the destructive interference of the
  out-of-phase sound from the back.

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Next Lecture Music _at_The Nexus

• Remember
• Guest Lecturer Brian Holmes