|Acoustics - PH 105
Vibrations and waves, perception and measurement of sound, musical instruments, the human ear and voice, electrical production of sound, acoustics of rooms, electronic music and environmental noise.
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Textbook: The Science of Sound, 3rd
Edition, Thomas Rossing, F. Richard Moore, Paul Wheeler, Addison Wesley (2002).
Instructor: David R. Renneke, Science 205, 309-794-3403, email@example.com.
Course syllabus (Word document) | How a CD Burner works | Noise reduction headsets
|Mar. 4||1||Introduction, survey, pictures, what is "sound", definitions of physical quantities (handout)|
|Mar. 6||2||Vibrations. Examples, amplitude, frequency, period, spring/mass system, radio frequencies (AM, FM, shortwave - WWV), NIST, pendulum, computer demos, time graph of periodic motion, oscilloscope|
Later we will return to the other examples in chapter 2: Helmholtz resonator, drumheads, vibrating bars and plates (xylophone, cymbals). Also, we will cover the vibration spectrum later (Section 2.7).
|Mar. 8||3||Waves. definitions of
transverse and longitudinal wave, examples, velocity = frequency x
wavelength, standing waves, sound waves in air,
Two videos: "Longitudinal Waves in a Helical Spring", #5, I, 3:45 (a) shows how the leading edge of a pulse compresses the medium and the trailing edges expands it. (b) each coil of spring undergoes SHM, (c) two pulses coming from opposite directions pass through each other, momentarily interfering constructively and destructively. "Longitudinal Standing Waves", #6, I, 5:20 - continuous longitudinal waves are produced by a variable-frequency mechanical driver and are reflected off of the fixed end. At certain frequencies, the interference produced a standing wave with nodes and antinodes, as illustrated with a strobe (blinking light). Model: the spring represents a standing sound wave in air and the coils represent air molecules. Note: vibration nodes = pressure antinodes, vibration antinodes = pressure nodes.
|Mar. 11||3, 4||Sound Waves. video: "Sources and Propagation of Sound", #1, II, 3:51. A vibrating tuning fork is examined with a strobe, computer animation, speaker and a "sensitive flame". Clint Sprott: 1. ringing bell in a vacuum jar, 2. inhale helium,... then inhale sulfur hexafluoride (density = r = 5 rair ). The velocity of sound in different media, change of velocity with temperature, Clint Sprott: 3. pipe filled with gas - shows standing sound waves. Reflection of waves (i = r), refraction of waves, video: "Reflection and Refraction of Waves in a Ripple Tank", #7, I, 3:32. Resonance of various systems - recall the video with the variable-speed jig saw and the string, tuning fork - in air and on a wooden box.|
|Mar. 13||3, 8.4||Interference of sound, "Sound
Divided into Two Paths of Differing Length", #5, II, 2:52.
One sound source is split into two paths of differing lengths.
Then the sounds paths are brought together and interfere.
Beats - occur when two waves of slightly different frequency are added. Demo: f=440 Hz, f=436 Hz, using two tuning forks. "Beat Phenomena", #6, II, 3:50. A beat pattern is produced (a) with two tuning forks of slightly different frequency and (b) with two electronically produced sound waves.
Diffraction - the property of waves that causes them to bend around obstacles. b = l/s. "Diffraction of Waves", #8a, I, 2:25 This shows how waves on a ripple tank take a curved path around a barrier. (stop at interference with two bobbers). "Bending of Sound Waves around an Obstacle", #7, II, 2:45. This illustrates how sound from a speakers bends around and obstacle and is received by a microphone.
Interference - the combination (or addition) of two waves traveling in the same medium at the same time. Demo: Pasco wave synthesizer 440Hz + 440 Hz. "Interference", #8b, I, 2:20. Two sources of waves on a ripple tank travel outward, overlap and interfere with another, shows places of constructive and destructive interference. Demo: Tuning fork - rotate.
|Mar. 15||3,4||Doppler effect, "Doppler Effect - Rotating Whistle" #8, II, 1:58. Two equations - observed freq. f' approaching (higher) ... and observed freq. f' receding (lower) ... Vibrating strings, Demo: vibrator and elastic string, corresponding drawing for 1, 2, and 3 loops. "Vibrations of a Guitar String" #6, III. Demos: guitar sound (keyboard), acoustic guitar (Lars Rehnberg). pages 208-209.|
|End of material that will be on Test 1.|
Vibrating air columns: closed
tube, open tube, computer demo #1 (local), computer
demo #2 - Web, End correction: add )=0.613 R at an open end (R =
inside radius of the tube), plastic tube, flue pipes (p. 323), slide whistle, 40-inch
organ pipe, 8-foot organ pipe.
|Mar. 20||2, 4, 13||
Do we need end corrections?
Experiment with a plastic tube 36.4 cm long with an inside diameter of
3.5 cm (measure,
calculate), Robert Greenler video: 1. whistle and rubber hose, 2.
build-a-sound, 3. recorders - long and short, 4. clarinet (10:00).
Helmholtz resonator - having fun with bottles. Mufflers. Robert Greenler video: 5. resonators - bottles, 6. Pepsi phone, 7. Hummer, 8. mentions bugle, trumpet, French horn, and tuba (5:50).
|Mar. 22||Test 1 - topics covered from Mar. 4-15. See the corresponding review sheet.|
|Mar. 25||2, 13||Vibrating bars. Robert Greenler video: vibrating rods, xylophone, Nailolian. Vibrating plates. 2 dimensional standing waves (lab), Video: "Chladni Plate" (#4, III, 3:22). Vibrating membranes. equation, demo. Drums.|
|Mar. 27||13||Doumbek drum - Middle Eastern hand drum - goat skin head - description - three basic sounds: DUM, TEK, KA - demo by Lars - music ("Jedeli"). Snare drum - demo. Steel drums - "Acoustics of Carribean Steel Drums", lecture by Dr. Thomas Rossing at Augustana on April 6, 2000. Science News article. Demo pan - Java applet - start with D4 and go up the scale. Listen to a CD (Trinidad Tripoli Steelband). Bells and carillons, handbells. video: "Resonant Modes of a Vibrating Bell using Holography", III, #5 (3:32). Cymbals, glass bell, wine glasses, Robert Greenler video: "Glass Harmonica" (6:00).|
|Apr. 3||5, 6||
Hearing - the human
ear, sound pressure, power and loudness. decibel
Demo: sound level meter - measure SPL
(sound pressure level) in dB.
CD: The Decibel Scale (1:57), #4 tracks 8-11: Broadband noise reduced in steps of 6 dB, then 3 dB, then 1 dB. Speech at these distances from the microphone: 25, 50, 100, 200 cm.
Adding sounds of the same frequency and different frequency.
Musician's scale (SSL in sones vs. LL in phons) - see p. 108 and 109. Handout.
|Apr. 10||6, 7||Masking - the obscuring of one sound by another. Handout. Hearing Loss - an increase of our threshold of hearing at certain frequencies. Handouts: Human audiogram, noise induced hearing loss. Noise reduction headsets (Bose®: $299). Partials - individual simple tones which make up a complex tone. Timbre (or quality) of a sound. Harmonics. CD: "Effect of Spectrum on Timbre", #28 track 53 (1:17). Sound synthesis - page 13. Fourier synthesis - adding harmonics. Demo: Pasco synthesizer.|
|Apr. 12||7, 9||
Fourier analysis - opposite of Fourier synthesis. Fourier
theorem... Video: "Fourier Analysis - Sound of a Trombone",
III, #7 (4:14). Sounds recorded in lab: 1
(tuning fork, panflute, telephone) - 2
(bottle, tuning fork, saxophone) - 3
- (guitar, trumpet, tuba). Formant of a tone - a frequency band
in the sound spectrum where most of the sound is concentrated. CD: "Effect of Tone Envelope
on Timbre", #29 tracks 54-56 (2:16). Vibrato - pitch
modulation, Tremolo - loudness modulation.
Chapter 9. Musical Scales and Temperament. Musical intervals and scales. Consonant and dissonant intervals. Interval names. Major triads - three notes sounded together with frequencies in the ratio 4:5:6 (for example F A C).
|Apr. 15||Test 2 - topics covered from Mar. 18 - Apr. 12. See the corresponding review sheet.|
Pythagorean scale, p. 176. Just diatonic
scale. Demo: TrueBASIC program.
Equal tempered scale. Interval for adjacent notes = twelfth root of 2 =
1.05946... Intervals expressed in cents. One octave = 1200 cents -
corresponding to 12 notes on the scale.
CD (handout): 18. "Logarithmic and Linear
Frequency Scales", tracks 34-35 (1:37)
Chapter 23. Auditorium Acoustics.
Sound absorbers. Anechoic rooms. Deere Technology Center anechoic room -
1 - photo
2 - photo
3. Reverberation - equation: RT = 0.061
V/A. Audio tape: (a) "Echo and
Reverberation", (b) UCLA reverberation room to test acoustic tiles
and other absorbers, anechoic room (one foot walls supported by inner
tubes) used to calibrate microphones, measure acoustic output, and test
CD (handout from last time): 35. "Effect of Echoes", track 70 (1:47). Graph of reverberation time vs. room volume. Calculations. Measurement of reverberation time - results for various places on campus, calculation for a classroom.
|Sound amplification, precedence effect, ringing, Video: "Tuning of Meyerhoff Hall" (15 min.) - take notes on the various design goals and techniques, outdoor music pavilion - Central Park in New York (handout).|
|Microphones and Loudspeakers. Transducers (devices that convert energy from one form to another), four microphone types: crystal (piezoelectric), dynamic (moving coil), condenser (capacitor), electret condenser (metalized plastic), dynamic loudspeaker, horn speakers, baffles and enclosures.|
|Apr. 26||27||Noise reduction headset. Electronic music (handout) - musique concrete, music by animation, computer-composed music (demo - "ILLIAC Suite for String Quartet", composer Lejaren Hiller, mathematician Leonard Isaacson - 1957), computer-played music (demo - Numerology), synthesized music, Arp Axxe keyboard, comparison of a violin and a synthesizer (handout), ADSR envelope (attack, decay, sustain, release).|
|Apr. 29||18||Sound synthesis (p. 137) - time graphs, sound spectrum. Filters (p. 409): low-pass, high-pass, band-pass, band-reject. Octave band analyzer, envelope generator (ADSR - attack, decay, sustain, release). Elements of a clarinet, patch for synthesizing a clarinet sound. Noise - white, pink. MIDI - musical instrument digital interface (p. 677).|
Digital Sound File
Chapter 10. String Instruments. Sound analysis of a tuning fork and a violin, the four strings: G3 (196 Hz), D4 (294 Hz), A4 (440 Hz) and E5 (660 Hz). Special thanks to Amanda Young for playing her violin in lab (Spring 2000) so these sounds could be recorded and analyzed. Parts of a violin, vibrations of a plucked string (snapshot), conclusions, motion of a bowed string.
Playing the violin, Demo:
Melissa Soluri, vibrational modes of the bridge, plate
resonance - holographic
interferometry (Augustana graduates: Josh Murphy and Craig
Schmaus - summer research) poster,
vibrations of the violin body (MWR - main wood resonance about 440 Hz),
vibration of the air cavity (MAR - main air resonance from 260 to 290
Hz), acoustical characteristics of violins (handout), piezoelectric
pickup, viola (tuned a 5th below a violin).
Digital audio compact discs (p. 509). 12 cm in diameter, 782 megabytes of data (74 min of audio), focused laser beam (1.7 micrometer diam.), red light - semiconductor laser (790 nm), read and record speed = 1.25 m/s, variable rotation rate - 500 rpm inside track, 200 rpm outside track, sampling time = 44,100 per second, freq. range 20-2000 Hz, dynamic range - 90 dB. Demo - laser beam reflecting off an audio CD, laser beam through a diffraction grating.
a CD Burner works. CD-R (record at 250 oC), CD-RW
(record at 500-700 oC, anneal or erase at 200 oC).
Speech production. Human vocal organs, glottal puffs (waveshapes, sound spectrum), resonator, resulting sound (waveshapes, sound spectrum), formants - peaks in the sound spectrum, shape of the vocal tract for various vowel sounds (i, ae, u).
Analysis of speech. Sound spectrograph, speech spectrogram, demo using Real Player Plus - "sound analyzer": spectrum, spectrogram, waveform, graph - 16 band frequency display.
Speech Production. Science New article - see below..
without Borders" - Science News, April 15, 2000, p.
252. This is an interesting article about singing birds and
musical compositions, e.g. some by Mozart. Four sonograms are
shown at the right: (a) warbler, (b) whale, (c) flute, (d) person.
Sonograms show frequency rising vertically as time progresses horizontally. Note that sonograms (the term used in this article) are equivalent to "sound spectrograms" as used by your textbook (and many others). Also notice that the time graph (waveshape) is shown along the top of each of these sonograms.
|Handout the review sheet for Test 3. 55 minute NOVA video: "What is Music?"|
|Course evaluation (about 20 min), demo: Mike Whiteside - steel drum that he made from a 55 gallon barrel. Time available for questions.|
Last update: May 8, 2002