Transcript Slide 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
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.
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, 7:30pm.
Turn in your ticket receipt (student tickets are $17).
Worth two quiz/participation credits.
Le Petit Trianon, 72 N. 5th St., San Jose
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.
Homework: Exploratorium
Located near Golden Gate Bridge.
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)
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.
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
Instruments:
Musical and Scientific
Hearing & Making Music
This lecture we finish the discussion on hearing
music and consider details of how to make it.
Loudness & Amplitude
Loudness depends on amplitude of pressure
and density variations in sound waves.
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.
Demo: Make Some Noise
Let’s 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.
Amplitude & Frequency
Perceived loudness contours for various frequencies and amplitudes
Low frequency and very high frequency sound requires high amplitude to be heard
Hearing by Age & Sex
Absolute thresholds of hearing by age in males and females
Male, Age 60
Male, Age 50
Female, Age 60
Male, Age 40
Male, Age 30
Male, Age 20
Hearing acuity decreases with age, especially in the high frequencies.
In general, women have greater acoustic sensitivity than men.
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?
Musical Instruments
Now that we understand more about the physics of
sound, let’s analyze how it is produced by different
types of musical instruments.
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
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
Brass & Woodwind Vibrations
Vibrations in a pipe created by:
• Vibrating one’s lips (e.g., trumpet)
• Blowing past an opening (e.g., flute)
• Blowing & vibrating a reed (e.g., clarinet)
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)?
Recorder & Pipe Organ
Oscillations in a pipe induced by pushing air
through the pipe.
Different length pipes for different notes
Recorder has finger-holes
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.
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
Vibrations in Woodwinds
What exactly creates the oscillations when
we blow into a woodwind instrument?
The Oboe Player,
Thomas Eakins, 1903
Bernoulli’s Principle
Still Air
A
Wind
Where the speed of a fluid
increases the pressure in the
fluid decreases.
This phenomenon is due to
energy conservation; when
fluid’s kinetic energy increases
(velocity increases) its internal
potential energy (pressure)
decreases.
L
Demo: Blow It Up
Hold a sheet of paper in front of your mouth
and blow; the paper will rise.
L
A
Check Yourself
Wind blowing over the ocean causes waves to
build due to Bernoulli’s principle.
Where is the pressure lowered?
L
L
A
A
A
Air moves fastest at the tops of the waves so pressure is lowest there.
The lower portion of the wave is blocked from the wind so air above
the water is at atmospheric pressure.
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 Orlean’s Superdome after hurricane Katrina
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.
Side view
A
L
Front
view
Demo: Blow the Funnel
Blow hard through a
funnel with a ping
pong ball in the
funnel’s bowl.
Instead of being
blown away, the
ball is held tightly
in the bowl.
BLOW
L
L
Ping
Pong
Ball
A
Airplane Wing
Pressure difference created by Bernoulli
effect creates upward lift.
LIFT FORCE
L
Wing
A
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.
L
A
L
A
A
A
L
A
A
L
Demo: Whirly Tube
Whirl a corrugated tube
to produce a pure
tone at the tube’s
natural frequency.
Bernoulli principle
creates low pressure
at the moving end,
drawing air through
the tube.
L
A
Whistling
Pressure difference between moving and
stationary air creates oscillating vortices.
Hole Whistling
L
A
A
L
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Whistling wires
Air
Air
A
Percussion Instruments
Create oscillations by
striking an object,
such as:
• Stretched drumhead
• Metal rod or disk
• Wooden object
• Stretched string
Evolution of the Piano
Dulcimer
Clavichord
Piano
Hammer
Harpsichord
Visit the Beethoven Center on the fifth floor of MLK library.
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
Loudness depends on:
• Amplitude of oscillation
• Mass of the string
• Frequency
Modern piano
has many long,
massive steel
strings under
high tension
(hundreds of
pounds) on a
large sounding
board.
Drum Heads
Drum heads are stretched
membranes that vibrate at
different frequencies
depending on the membrane’s
oscillation pattern.
Note: These animations are not accurate because complex patterns should oscillate faster.
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, they’re just smaller.
Constructive Interference
Two waves in phase add together, which is
called constructive interference.
Destructive Interference
Two waves out of phase cancel each other
out, which is destructive interference.
In & Out of Phase
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
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
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.
Next Lecture
Music @
The Nexus
Remember:
Guest Lecturer: Brian Holmes