Acoustics - PH 105
Spring, 2001
Standing Wave

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.


Textbook:  The Science of Sound, 2nd Edition, Thomas Rossing, Addison Wesley (1990).
Instructor:  David R. Renneke, Science 205, 309-794-3403, phrenneke@augustana.edu.
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Date Chapter Topics
Mar. 5 1 Introduction, survey, pictures, what is "sound", definitions of physical quantities (handout)
Mar. 7 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. 9 3 Waves.   definitions of transverse and longitudinal wave, examples, velocity = frequency x wavelength, standing waves, sound waves in air, sound creation with a tuning fork, two short videos
Mar. 12 3, 4 velocity of sound in different media, change of velocity with temperature, reflection of waves (i = r), refraction of waves, resonance  of various systems
Mar. 14 3, 8.4 interference of sound, beats, diffraction, interference (water waves, electronic sound, tuning fork)
Mar. 16 3,4 Doppler effect, video: "Doppler Effect - Rotating Whistle" (II, #8), vibrating strings, demo: vibrator and elastic string, video: "Vibrations of a Guitar String" (III, #6), demos: guitar sound (keyboard), acoustic guitar (David Spaude), video: "Washtub bass" (5:00).
End of material that will be on Test 1.
Mar. 19

3, 4

Vibrating air columnsopen tube, closed tube, computer demo, flue pipes, whistle, 4 foot organ pipe, videos: "Cork Dust ..." (III, #1, 4:35), "Gas Flame" (III, #2, 4:43)
Mar. 21

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 min).
Helmholtz resonantor - having fun with bottles.  Mufflers.
Mar. 23   Test 1 - topics covered from Mar. 5-16.  See the review sheet handed out earlier.
Mar. 26 2, 13  Vibrating bars.  video: vibrating rods, xylophone, Nailolian.  Vibrating plates. 2 dimensional standing waves (lab), video: "Chladni Plate", IIi, #4 (3:22).  Vibrating membranes.  equation, demo.  Percussion Instruments.
Mar. 28 13, 5 Steel Drums.   "Acoustics of Carribean Steel Drums", lecture by Dr. Rossing on April 6, 2000.    Science News article.   Demo pan - Java applet - start with D4 and go up the scale.   Listen to a drum band at NIU.  Bells and carillons, handbells. video: "Resonant Modes of a Vibrating Bell using Holography", III, #5 (3:32).  Hearing - the human ear
Mar. 30 13, 6 Cymbals, glass bell, wine glass, video: "Glass Harmonica", Sound pressure, power and loudness.  decibel scale

Typical Sound Pressure Levels (SPL) in Decibels (dB) - Other values on page 86.

200

 noise weapon 85  outboard motor
155  can burn skin 74  vacuum cleaner
145  jet at takeoff 68  normal conversation
128  machine gun 55  office
120  threshold of pain 45  living room
117  loud auto horn 35  library
115  rock band 20  whisper
108  circular saw, motorcycle 10  rustling leaves
95  lawn mower, heavy traffic 0  threshold of hearing
Apr. 2 6 Demo: sound level meter - measure SPL (sound pressure level) in dB.
CD:  The Decibel Scale (1:57), adding sounds of the same frequency and different frequency, musician's scale (SSL in sones vs. LL in phons).
Apr. 4 6, 7 Equation relating SSL and LL.  Masking.  Hearing Loss.  Harmonics.  Partials.  Timbre.  Sound synthesis.  Fourier analysis.
Apr. 6 7, 9 Video: "Sound of a Trombone", III, #7 (4:14).  Sounds recorded in lab: 1 - 2 - 3. Formants.  CD: "Effect of Tone Envelope on Timbre".  Vibrato and tremolo.
End of material that will be on Test 2.

Musical intervals and scales.   Consonant and dissonant intervals.  Pythagorean scale.
Apr. 9   Test 2 - topics covered from Mar.19 - Apr. 6
Apr. 11 9 Just diatonic scale.  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. Linear and Logarithmic Frequency Scales, 16. Stretched and Compressed Scales, 27. Circularity in Pitch Judgment.
Apr. 18 23 Auditorium acoustics.  Sound absorbers, anechoic rooms, reverberation.
Apr. 23 23, 24 Measurement of reverberation time, calculation for a classroom,  sound amplification, precedence effect, ringing,  video: "Tuning of Meyerhoff Hall" (15 min.), outdoor music pavilion - Central Park in New York (handout).
Apr. 25 20 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. 27 26, 27, 29 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. 30 19 Sound synthesis (p. 128) - time graphs, sound spectrum.  Filters: 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.
May 2 29, 10 Digital sound file formats.
File extension Description Comments
.mid MIDI - musical instrument digital interface Real Player
(free download)
.wav Windows audio file
Can record with "Sound Recorder" 
or Cool Edit.
WinAmp 
Cool Edit
.voc voice file Sound Blaster 
(lab experiment)
 "play" and "vedit"
.mp3 CD quality compressed files various players
(see above)
.nwc design to compose music - can also save
as a MIDI format (.mid) or load a MIDI file.
NoteWorthy Composer
.rmi small sound files Microsoft
 

Digital Sound Files

  • MIDI sound - midi.org (MIDI Information, What is MIDI?) | midi.com (About MIDI, What is MIDI?) | sample files:  .mid (1, 2, 3) | classical midi page
  • mp3 sound - mp3.com | sample files:  .mp3 (1, J.S.Bach)
  • Two types of sound files from Windows:  .wav (1, 2, 3, 4, 5, 6, 7)  and  .rmi (1, 2, 3)
  • NoteWorthy Composer - A shareware software music composition and notation processor for Windows.  It allows you to create, record, edit, print, and play back your own musical scores.  The file extension is .nwc.  You can export these files to .mid and you can import .mid files into NoteWorthy Composer.  You can use an external MIDI keyboard for real-time and step-time entry of your music.  The keyboard used in the Musical Scales experiment has a MIDI interface.
  • Sound Blaster Live

String instruments - Chpt. 10.  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.
May 4 10, 28 Playing the violin, vibrational modes of the bridge, plate resonance - holographic interferometry (Augustana graduates: Josh Murphy and Craig Schmaus - summer research), 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).

Digital audio compact discs (p. 568).  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.

May 7 15, 16 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.  Science New article - see below.

Speech Production

  • Talking Heads:  Speech Production - research being done at Yale University

Science News magazine "Music 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.

 

 Last update: May 7, 2001