Acoustics

PIRA classification 3C

3C10. The Ear

3C10.10 model of the ear 3C10.20 time resolution of the ear 3C10.20 binaural hearing Hold the ends of a long tube to each ear and have someone tap in the center and then a few centimeters to each side. 3C10.21 direction judgment of the ear High frequency location depends on difference in intensity produced by the shadow of the head. 3C10.21 direction judgment of the ear Location of low pitched sounds depends on phase difference. Use a model stethoscope with one tube longer than the other. 3C10.30 bone conduction

3C20. Pitch

3C20.10 range of hearing Use an oscillator driving a good audio system to demonstrate the range of hearing. 3C20.10 range of hearing A set of good speakers is used to test the student's range of hearing. 3C20.10 range of hearing An oscillator driving a good audio system is used to demonstrate the range of hearing. 3C20.11 range of hearing Use whistles, forks, etc. to establish upper range of hearing or an audio oscillator from 10 to 30,000 Hz. 3C20.15 Galton whistle The Galton whistle can be adjusted to produce an intense sound into the ultrasonic range. 3C20.16 ultrasonic waves A set of steel rods tuned to frequencies up to 30 KHz are struck with a hammer and the sound both heard and displayed on an oscilloscope. 3C20.17 ultrasonic vibrations of quartz Making an ultrasonic transducer and using it to make a fountain and emulsion. 3C20.20 zip strips 3C20.25 musical bottles Blow across a set of bottles with water levels adjusted to give a scale. 3C20.30 siren disc An air jet is directed at a rotating disc with holes. 3C20.30 siren disc Air is blown through concentric rows of regularly spaced holes on a spinning disc. Change of speed of the disc changes frequencies but not intervals. 3C20.30 siren disc A disc with concentric ring of equally spaced holes is spun by a motor and a jet of air is blown at each circle of holes. 3C20.40 frequency and pitch A set of gears on a single shaft of a variable speed motor have the ratios of 44-47-49-52-55-59-62-66-70-74-78-83-88. 3C20.40 musical saw A card is held against a dull saw as the speed is varied. 3C20.40 tooth ratio scale A set of gears with 44-47-49-52-59-62-66-70-74-83-88 teeth are mounted coaxially on a shaft connected to a variable speed motor. Varying the speed shows intervals are determined by frequency ratios rather than absolute pitch. 3C20.40 Savart wheel Hold a stiff cardboard against the rim of a spinning toothed wheel. Use wheels on the same shaft each with different numbers of teeth. 3C20.40 Savart's wheels A major chord is produced when a cardboard is held against rotating wheels with tooth ratios of 3:4:5:6. 3C20.40 gear and card Hold a card against gears on a common shaft with teeth in ratio of 4:5:6:8. 3C20.41 saw blade organ Several saw blades are mounted on the same rotating shaft with sound produced by amplifying the output of a coil pickup. A band of switches selects the active blades, allowing chords to be played. 3C20.45 pitch sort of Many examples of sound of poor quality but with some definite pitch. E.g., a thumbnail on a book cover. 3C20.70 sound cart All the instrumentation for a physics of sound course is loaded on one mobile cart.

3C30. Intensity and Attenuation

3C30.20 dB meters and horn Place dB meters in the class at 2 meter intervals, then blow a loud horn. 3C30.21 dB meter and horn An air horn driven by a compressed air tank gives a 120 dB sound at close range. Use a dB meter to measure the intensity at various ranges. 3C30.21 air horn A railroad horn blown from a tank of compressed air has a nearby intensity of 110 dB. 3C30.22 sound level meter A sound level meter is used to measure the instructor speaking, etc. 3C30.30 loudness (phones and sones) 3C30.35 hearing -3dB A function generator with a dB meter is used to quickly adjust to half power. 3C30.36 3 dB One and two students pound the table equidistant from an observer. 3C30.41 attenuation of materials place various materials between a sounding board and a tuning fork stuck in a block of wood. 3C30.42 modified tuning fork resonance box The tuning fork is removed from a resonance box and a rod, string, and water are interposed. 3C30.43 attenuation in CO2 A high pitched tone transmitted through a 10' pipe will be attenuated when filled with CO2. 3C30.45 acoustical tiles Show various acoustical tiles.

3C40. Architectural Acoustics

3C40.10 room reverberation time Go around and record pistol shots in various rooms, then determine reverberation time at different frequencies with some equipment in the classroom. 3C40.10 reverberation time Students clap hands to generate sound for reverberation time. 3C40.10 reverberation time Study the reverberation time of a room. 3C40.10 reverberation time Measure reverberation time of the classroom with a dB meter. (-60dB) 3C40.11 reverberation tube Measure the time required for sound to die in a tube that can be fitted with caps of various materials. 3C40.20 ripple tank acoustics Cross sectional models of various auditoriums are used in a ripple tank to show scattering and reflection.

3C50. Wave Analysis and Synthesis

3C50.10 Pasco Fourier synthesizer The Pasco Fourier synthesizer allows one to build an arbitrary waveform with up to nine harmonics. 3C50.10 Pasco Fourier synthesizer The Pasco Fourier synthesizer is used to build up a square wave. 3C50.10 Pasco Fourier synthesizer The Pasco Fourier synthesizer allows one to build an arbitrary waveform out of up to nine harmonics. 3C50.10 Fourier synthesizer Use the Pasco Fourier synthesizer to demonstrate building square and triangle waves. 3C50.12 electronic music synthesizer The principles of an electronic music synthesizer and its use in demonstrations. 3C50.12 electric organ as synthesizer The timbre of a musical note is demonstrated by showing an oscilloscope trace of an electric organ while changing the drawbars. 3C50.13 electromechanical Fourier synthesize A set of eight mechanically geared potentiometers generate sine/cosine waves and harmonics. 3C50.13 mechanical multichannel generator A four channel mechanical signal generator is used to show a fundamental and two harmonics. Picture. Construction details in appendix, p. 626. 3C50.14 synthesizer The PAiA 2720 Synthesizer used with an oscilloscope for ten demonstrations. 3C50.14 waveform synthesizer Oscillators tuned to 1, 2, 3, 4, and 5 Khz have variable amplitude and phase. External input and an audio amp are also included. 3C50.14 waveform synthesizer A waveform synthesizer based on the Intel 8748 microcontroller is described along with some theory and an experiment. 3C50.15 mechanical square wave generator Shadow project a mechanism with a small disc mounted at the edge of a larger disc with 1/3 the diameter geared to rotate 3 times as fast as the larger disc. 3C50.18 arbitrary waveform generator Sweep a high freq signal at a low freq on an oscilloscope with a mask cut out to the shape of the wave desired and look at it with a photocell. 3C50.30 Helmholtz resonators and microphone Hold a small microphone individually to a set of Helmholtz resonators. 3C50.31 Helmholtz resonator Sound from a loudspeaker is directed at a series of Helmholtz resonators with pinwheel detectors at their small apertures. 3C50.31 ganged resonance boxes A pistol is fired in front of a set of tuning fork resonance boxes equipped with inductive pickups. Picture. 3C50.33 resonance in a box A complex setup to plot the frequency spectrum of a box. Pictures, Diagrams. 3C50.34 resonant response of vocal cavities Use a fake larynx to talk without using the vocal cords. 3C50.35 resonance tube spectrum Drive a speaker at one end of a tube with the swept frequency output of a spectrum analyzer. 3C50.36 air column resonance spectra Use a storage scope and two function generators to display the swept spectrum. Interesting additions are end corrections, tone holes, and adding a bell. 3C50.37 radiation patterns of horns Feed a oscillator or other sound to any one of four different types of horns to show differences in quality at various frequencies. 3C50.40 harmonic tones (vibrating string) 3C50.40 string resonance spectra on oscillo. Sweep the source generator and oscilloscope horizontal from a generator. Use a steel wire and guitar pickup. 3C50.40 resonances in strings Excite a steel string with a linearly swept sinusoidal signal and show the output on a spectrum analyzer or storage oscilloscope. 3C50.50 noise (pink and white) 3C50.55 distinguishing harmonics A generator with an adjustable high Q bandpass filter allows one to train the ear to pick out the harmonics of a complex sound. 3C50.55 distinguishing harmonics The circuit diagram for the Gronseth device. 3C50.70 wave analysis (PASCO filter) 3C50.80 spectrum analyzer 3C50.81 RLC bank harmonic analyzer A bank of RLC circuits covering to the tenth harmonic of 235 Hz is used as a harmonic analyzer. Diagram. 3C50.82 LC harmonic analyzer Sweep a square wave generator through a single LC filter and detect maxima at harmonics of the fundamental. 3C50.83 low cost spectrum analyzer A circuit for a 100 kHz spectrum analyzer using a standard oscilloscope for display. 3C50.83 spectrum analyzer - Tek 5L4N The Tek 5L4N spectrum analyzer plug-in is used with a camera (instead of a storage scope) to show the spectrum of sustained tones from musical instruments at different pitch and loudness. 3C50.94 FFT on 6502 A FFT algorithm relocatable to any 6502 is available from the author. 3C50.94 microcomputer based analyzer Discusses algorithms for cross correlation and sound intensity analysis.

3C55. Music Perception and the Voice

3C55.20 pitch of complex tones Use an Apple computer to generate complex tones. Students judge the pitch. 3C55.25 missing fundamental Microcomputers with built-in tone generators are handy for generating "missing fundamental" demonstrations. 3C55.26 sing/whistle - which octave Whistle and sing into a three foot pipe and use the resonances to show your whistling range is much higher than your singing range. 3C55.30 difference tones 3C55.30 subjective tones A toy whistle emits tones at 2081, 1896, and 1727 Hz. Subjective difference tones at 169, 185, and 374 Hz are clearly audible. 3C55.31 combination tones and the ear Explanation of how the nonlinear ear creates difference tones and common examples of the phenomena. Two demonstrations: sweep with a second oscillator to find the difference tone, add 200, 300 and 400 Hz to hear 100 Hz. 3C55.35 difference tones and beats Two pure tones produce beats or difference tones. Theory and a demonstration that trains our ears to hear and distinguish the two. 3C55.35 beats on scope, difference tones The usual two oscillators, amplifier, and scope. For difference tones, set one oscillator above the audible range and the difference tone is the only thing the student can hear. 3C55.35 beats on scope, difference tones Two audio oscillators drive two speakers. A microphone pickup displays the sum on an oscilloscope. ALSO - difference tone. 3C55.40 chords Using the three string sonometer to study the structure of chords by varying the bridge location of strings tuned in unison. 3C55.41 circular glockenspiel Mallets can be put in any of twelve holes on a spool to play major, minor, augmented, and diminished cords on a circular glockenspiel. 3C55.42 consonant musical interals Consonant and dissonant intervals are explained by a relation between the time required to perceive a definite pitch and the period of a complex tone. 3C55.45 consonance and dissonance 3C55.45 harmonious notes Using the sonometer to demonstrate the harmonic content of different interval combinations. 3C55.50 musical scale 3C55.51 numerical investigation of scales An investigation of why the 12 note scale is the best equal tempered scale. 3C55.51 quanitiative investigation of scales A quantitative measurement of how well any tuning succeeds in providing just intonation for any specific piece of music. 3C55.51 scales and algebraic groups On transposing. 3C55.52 lucky equal temperaments An analysis of how good the fits of 12, 19, 31, and 53 steps per octave are in equally tempered scales. 3C55.55 piano tuning On making use of instrumentation to help with piano tuning. 3C55.55 piano tuning A pianist discusses the finer points of piano tuning. 3C55.55 piano tuning On "stretching" the equally tempered scale. 3C55.55 tuning forks with resonators A set of tuning forks mounted on resonance boxes make the musical scale. 3C55.55 tuning fork resonance boxes A set of four different tuning forks on resonant boxes. 3C55.55 tuning forks on resonant boxes Two tuning forks, two boxes. Show the box needs to be matched to the fork. 3C55.60 Johnson intonation trainer A small organ that is switched between fixed and variable tuning to demonstrate even tempered and just intonation. 3C55.65 tone quality A series of organ pipes tuned carefully to give the harmonics of a fundamental can be used to show the effect of suppressing various harmonics. 3C55.70 microphone and oscilloscope Show the output of a microphone on an oscilloscope. 3C55.71 sound wave on oscilloscope Show a sound wave on the oscilloscope while listening to it. 3C55.72 tone quality Using a microphone and oscilloscope, demonstrate that a tuning fork does not produce a pure sine wave but a fork on a resonance box does. 3C55.73 tone quality of a Boehm flute Harmonic analysis of rich and dull tones from the Boehm flute. 3C55.74 keyboard and oscilloscope 3C55.75 forms of sounds A variant of the circuit produces roulette figures, etc. 3C55.75 voice display - corridor demo A circuit to advance the horizontal 45 degrees and retard the vertical 45 degrees to give a circular trace when a falsetto "o-o-o" is sung. 3C55.80 formants Sing formants into a HP analog spectrum analyzer. 3C55.80 vocal formants Use an computer based real time spectrum analyzer to display vocal formants. 3C55.82 tone quality Using a phonelescope or oscilloscope, sing the different vowels at the same pitch and the same vowels at different pitches. 3C55.85 filtered music and speech 3C55.85 octave-band filters Use an octave-band filter (from an audio store) to demonstrate filtered music and speech. 3C55.90 Book/CD review - piano acoustics Review of a book "Acoustics of the Piano" that comes with a CD that includes examples used in the lectures. 3C55.90 musical sound records The Science of Sound - Bell Labs, Energy and Motion - Zaret and Singer, Experimental Songs - Dorothy Collins, Space Songs - Tom Glazer & Dottie Evans, Physics Songs - State University of Iowa. 3C55.99 churchbell guitar Swing a guitar back and forth as it is plucked to mimic a church bell.

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