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, 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

4. 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)

7. 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

9. 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.

13. 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.

14. Amplitude & Frequency Perceived loudness contours for various frequencies and amplitudes Low frequency and very high frequency sound requires high amplitude to be heard

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

16. 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, let’s analyze how it is produced by different types of musical instruments.

18. 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

19. 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 one’s lips (e.g., trumpet) • Blowing past an opening (e.g., flute) • Blowing & vibrating a reed (e.g., clarinet)

21. 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.

24. 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

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

29. 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

30. A L Side view 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

31. L L A Demo: Blow the Funnel BLOW 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. Ping Pong Ball

32. Airplane Wing Pressure difference created by Bernoulli effect creates upward lift. LIFT FORCE L Wing A

33. L A A L A A A L A L 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 tube’s 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.

38. 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 membrane’s 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, they’re just smaller.

41. 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.

43. In & Out of Phase

44. 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.

47. Next LectureMusic @The Nexus Remember: Guest Lecturer: Brian Holmes