||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.|
|Textbook: The Science of Sound, 3rd
Rossing, F. Richard Moore, Paul Wheeler, Addison Wesley (2002).
Instructor: David R. Renneke, Science 205, 309-794-3403, firstname.lastname@example.org.
Course syllabus (Word document) | class list | videos | bottom of the page
Test 3 - 3:00 pm, Tuesday, Feb. 22. Chapters 9,10,15,16,19,20,23,24,26-29
|Nov. 29||1||Introduction, survey, pictures, what is "sound", definitions of physical quantities (handout)|
|Dec. 1||2||-- Vibrations: examples,
amplitude, frequency, period, spring/mass system, radio frequencies (AM,
FM, shortwave - WWV), NIST, time
-- Pendulum: equation for the period T, demo: 3 different lengths, computer demos (Interactive Physics), time graph of periodic motion, demo: 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).
|Dec. 3||3||-- Damped vibrations: demo:
mass on a spring - friction with air vs. water.
-- Waves: definitions of transverse and longitudinal wave, demo: examples (clothes line, wave machine, slinky), velocity = frequency x wavelength, (v = f l)
-- Standing waves: definition, demo: clothes line, wave machine
-- Sound waves in air: definition, demo: 440 Hz tuning fork, plastic tube (resonant air column), Computer animation (longitudinal waves)
|Dec. 6||3, 4||-- Longitudinal waves -
-- Longitudinal standing waves - Video 3
-- Sources of sound (tuning fork, speaker) - Video 4
-- Velocity of sound in different media - air, helium, sulfur hexafluoride - Video 5
-- Change of velocity with temperature, v = 331.5 + 0.61 t, t = Celsius temperature
demo: two wave machines, two speeds
-- Reflection of waves (i = r), demo: ball, wave machine
-- Refraction of waves - definition - Video 6 - constant f, v and l change
-- Sound refracts down over a frozen lake, up over a hot highway, up against wind (p. 53)
-- Resonance - definition - e.g. swing, demo: tuning fork - in air and on a wooden box
|Dec. 8||3, 8.4||-- Video 7 - "Sound Divided
into Two Paths of Differing Length"
-- Beats: They occur when two waves of slightly different frequency are added. For sound waves, we "hear" beats (sound waxes and wanes), demo: f=440 Hz, f=436 Hz, using two tuning forks, Video 8
-- Diffraction, Video 9, Video 10
-- Interference, Video 11
|Dec. 10||3, 4||-- Doppler effect, Video
12. 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. Video 13. demo: guitar sound (keyboard)
|End of material that will be on Test 1.|
|Dec. 13||4||-- Guitar demonstrations (Katy Wilford,
Dennis Dixon), acoustic guitar, pages
electric guitar and mandolin, pages 217-219.
-- Vibrating air columns: closed tube, open tube, computer demo (standing waves), Java applet
-- End correction: add 0.613 R at an open end (R = inside radius of the tube)
-- Demos: plastic tube, flue pipes (p. 323), slide whistle, 40-inch organ pipe, 8-foot organ pipe
-- Video 14 - Standing sound waves are revealed by cork dust in a glass tube.
-- Video 15 - Illuminating gas in a one-meter metal flame tube. Return to the Java applet - third arrangement - closed at both ends
|Dec. 15||2, 4, 12||-- Resonant air
column experiment: plastic tube (La = 36.4 cm, R = 1.75
cm), function generator and a speaker, calculate the effective length
(open at both ends), measure the air temperature, calculate the velocity
of sound, calculate the fundamental frequency, then measure it and
compare. Repeat the experiment with the tube closed at one end.
-- Video 16 - demos of whistle and a rubber hose, pop bottle, Hummer
-- Cavity (Helmholtz) resonator (p. 67) - a vibrator consisting of a volume of enclosed air with an open neck or port. Equation to calculate the resonant frequency...
-- Examples: 1. various bottles (p. 263), demo - boiling liquid nitrogen in a singing teakettle, 2. the air cavity in violins and guitars, 3. air cavity in a bass reflex loudspeaker - demo - oscillating flame near the port hole, 4. mufflers (p. 68)
|Dec. 17||Test 1 - Chapters 1-3, Sections 4.1-4.3, 8.4.|
|Jan. 3||2, 13||
-- Video 17 - demos of resonators
(bottles), Pepsi phone, Hummer
-- Sound of the flute - effect of temperature - increase T, decrease density, increase f, lengthen the tube to compensate (keep it in tune). Using helium instead of air has the same effect.
-- demo - flute (Betsy Wolin) - p. 262-266.
-- Vibrating bars, demo - tuning fork with f1 = 320 Hz, f2 = 6.25 x f1 = 2000 Hz
-- Tuned bar (two supports), demo - Gamut bells
-- Video 18 - demos of vibrating rods, xylophone, Nailoian
-- Vibrating plates (2 dimensional standing waves)
-- Video 19 - Chaldni plate - p. 33, lab
-- Vibrating membranes, demo - change the diameter and the tension
|Jan. 5||13||-- Transverse
vibrating bars and rods
3 vibrating bars (A6 - 1760 Hz, E7 - 2637 Hz, A7 - 3520 Hz), wind chimes, demo
-- Drums - snare drum (p. 288-289), other drums, demo
|Jan. 7||13||-- demo - cymbals, pan covers (large, small)
-- bells and carillons (old instruments) - 8 modes, strike note
-- demo - glass bell, Video 20 - "Resonant Modes of a Vibrating Bell using Holography", III, #5 (3:32).
-- demo - wine glass, Video 21 - "Glass Harmonica", 6:00.
-- steel drums - "Acoustics of Carribean Steel Drums", lecture by Dr. Thomas Rossing at Augustana on April 6, 2000. Demo pan - Java applet - start with C4 and go up the scale.
-- steel pan - made by Mike Whiteside - making a pan
|Jan. 10||5, 6||-- Hearing - the human
ear, sound intensity
-- sound intensity, sound pressure, audio demo: "Intensity", decibel scale
|Jan. 12||5, 6||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.
|Jan. 14||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.
-- Fourier analysis - opposite of Fourier synthesis.
-- Fourier theorem... Video 22: "Fourier Analysis - Sound of a Trombone", III, #7 (4:14).-
- "Measurements of Noise Levels in the Wood Shop" (5:50).
-- Using noise to cancel noise - BYU physicist Scott Sommerfeldt quiets fans in computers - article
-- 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). Pythagorean scale, p. 176.
|Jan. 19||9||Origin of the Pythagorean scale. Just diatonic scale. Demo: TrueBASIC
program (narrated audio tape). 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)
|Jan. 21||Test 2 - Topics covered from Dec. 13 to Jan. 17.|
16. "Stretched and Compressed Scales", tracks 32 (0:59)
|Jan. 26||23 24||
Demo: keyboard and mike - 1200 watt sound
mixer used in Science 102 -
front panel - speaker. Showed (a) how to increase the
reverberation time to correspond to larger rooms, (b) how to add delay
time, (c) feedback - high pitch squeal.
Calculations of reverberation time. Measurement of reverberation time - results for various places on campus, calculation for a classroom. Outdoor music pavilion - Central Park in New York (handout).
Sound amplification, precedence effect,
Video 25. "Tuning of Meyerhoff Hall" (15 min.) - take notes on the 8 design goals and techniques.
Photos of the ensemble room in Bergendoff Hall: 1, 2, 3, 4, 5, 6
Sound system components.
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 - Demos: show sound interference (cancellation). Demo: Speaker systems: regular portable radio vs. Bose Wave radio (1 meter long resonant air channel connected to the back of one speaker to effectively amplify low frequencies).
Electronic music (handout) - musique
concrete, music by animation, computer-composed music.
audio - "ILLIAC Suite for String Quartet", composer Lejaren Hiller, mathematician Leonard Isaacson - 1957, computer-played music (audio - Numerology), synthesized music, Arp Axxe keyboard, comparison of a violin and a synthesizer (handout), ADSR envelope (attack, decay, sustain, release).
|Feb. 4||24||For those who were absent on Jan. 28 - Repeat showing of Video 25. "Tuning of Meyerhoff Hall" (15 min.) - take notes on the 8 design goals and techniques.|
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).
MIDI Manufacturer's Association (midi.org).
A MIDI file doesn't contain actual audio data, but rather contains commands that let MIDI-capable synthesizers re-create a specific musical passage. The MIDI protocol has been used since 1982 as a way for electronic musical instruments (like digital keyboards and sequencers) to communicate with each other.
Computer sound cards typically feature the ability to interpret MIDI files into music. Since they don't actually contain the music itself, but rather the commands used to re-create music, MIDI files are a lot smaller than audio files like .mp3, .wma, or .wav. MIDI files are small and manageable enough that it's not uncommon to find them embedded in Web pages. MIDI files have the .mid filename extension.
|Feb. 9||29 10||
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).
The sound of a
ringing bell. Further explanation of the
sound and ringing of
church bells by Bill Hibberts. He also provides an excellent,
free program called
Wavanal (for a PC) that generates the sound spectrum (does a Fourier
analysis) of the sound contained in any .wav file.
Conclusions about plucking a string, motion of a bowed string - slip and stick, playing the violin, demo: Amanda Fenton, 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).
CDs - digital audio compact discs (p. 509) (handout). 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 clear CD and a diffraction grating. The distance between tracks on a CD and lines on a grating can be determined from diffraction measurements.
How a CD Burner works. CD-R (record at 250oC), CD-RW (record at 500-700oC, anneal or erase at 200oC).
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).
system of Hideyuki
Sawada (Kagawa University, Japan) - voice1 | voice2
|Feb. 16||Video 26 - "What is Music", NOVA program (55:00)|
Course evaluation - Kelly Atkins, about 20
Speech recognition in Word - installation - beginner's instructions - demo
Allen 320 Renaissance organ - description, photographs, recording by Tom Robin Harris
Test 3 - 3:00 pm, Tuesday, Feb. 22.
Topics from Chapters 9,10,15,16,19,20,23,24,26-29.
Material covered from Chapter 9 (Musical Scales) to the end of the course.
Last update: Feb. 15, 2005