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

Le Petit Trianon, 72 N. 5th St., San Jose

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.

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,LindaFor 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.

DecibelsLoudness 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.

SoundMeter

Start clapping softly and slowly increase or decrease loudness, as I direct you using the sound meter.

Amplitude & Frequency

Low frequency and very high frequency sound requires high amplitude to be heard

Perceived loudness contours for various frequencies and amplitudes

Hearing by Age & Sex

Hearing acuity decreases with age, especially in the high frequencies.In general, women have greater acoustic sensitivity than men.

Absolute thresholds of hearing by age in males and females

Male, Age 20

Male, Age 30

Male, Age 40

Male, Age 50

Male, Age 60

Female, Age 60

Hearing Loss

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.

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.

What?

Musical InstrumentsNow 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.

Valves used to vary the length through in 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.

Woodwind Instruments

Resonant standing waves also produced in a pipe but the pipe length varied by air holes (finger-holes, keys, or pads).

Flute

Clarinet

Saxophone

Oboe

Bassoon

Meter stick

Cor anglais

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.

Recorder has finger-holes

Different length pipes for different notes

Demo: Hoot TubesLarge 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

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.

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Still Air

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Demo: Blow It Up

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

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Check YourselfWind blowing over the ocean causes waves to build due to Bernoulli’s principle.Where is the pressure lowered?

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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 RoofIf wind blows hard

enough the low pressure above can create a large enough force to lift the roof off.

New Orlean’s Superdome after hurricane Katrina

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Demo: Blow It Off

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

Side view

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Fast moving air in the channel between the card and the table creates a low pressure region, pressing the card downward.

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.

PingPongBall

BLOW

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Airplane Wing

Pressure difference created by Bernoulli effect creates upward lift.

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Wing

LIFT FORCE

Demo: Keep It UpObjects in a moving steam of fluid are pulled to the center of the

stream because pressure is lower inside the stream than outside.

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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.

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Wire

Whistling

Pressure difference between moving and stationary air creates oscillating vortices.

Whistling wires

Hole Whistling

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Percussion InstrumentsCreate oscillations by

striking an object, such as:

• Stretched drumhead

• Metal rod or disk

• Wooden object

• Stretched string

Evolution of the Piano

Dulcimer

Harpsichord

Clavichord

PianoHammer

Visit the Beethoven Center on the fifth floor of MLK library.

String InstrumentsStanding 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 ofPhase

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