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Acoustical & Musical Instruments

  • H3-72: TUNING RODS

    H3-72
    Hear longitudinal standing wave resonances in aluminum rods.
    Hold the tuning rod by the center fixture and strike it longitudinally on its end with a rubber mallet to excite the standing wave. The three rods pictured are calibrated: 5000 Hz, 10,000 Hz, and 15,000 Hz.

  • H3-73: TUNING RODS - SUSPENDED

    H3-73
    Illustrate transverse standing waves in aluminum rods.
    Hold the series of rods by the wooden dowel and strike a rod sharply at its center to excite the lowest frequency transverse standing wave. Alternatively, strike the end of the rod to excite the lowest longitudinal vibration mode.
    H3

  • H3-74: TUNING BAR PARADOX - EFFECT OF WIDTH

    H3-74
    Illustrate transverse vibrations of a solid bar struck in the center.
    When struck on top center with a rubber mallet, like a xylophone or marimba, the narrower bar on the right in the photograph above vibrates with a frequency f.

    Q: Will the frequency of the larger bar on the left, which has the same length and thickness as the smaller bar, but twice the width, be greater than, less than, or the same as the frequency of the smaller bar?

    A: The frequency will be the same for transverse vibrations

    H3

  • H4-13: PLAYING IN JUST INTONATION

    H4-13
    Show musical intervals in just intonation.
    Musical intervals between the oscillator and an instrument or voice are played so as to create stable Lissajous patterns on the oscilloscope. These stable patterns result from frequencies in the ratio of whole numbers, corresponding to "just" or beatless musical intervals. This can require practice; consider inviting musically inclined students to try it out ahead of time.
    H4, ME2, ME3

  • H4-16: TUNER - KORG

    H4-16
    Demonstrate use of an electronic tuner.
    The tuner can be used to produce notes in tune in the equal tempered scale or to compare the frequency of notes from an external source with a standard stored in the instrument. It displays errors on an analog meter
    H4

  • H4-21: EDGE TONES

    H4-21
    Illustrate edge tones and the factors that effect their sound.
    Compressed air is blown out a slit onto the point of a wedge-shaped barrier. The wedge can be positioned with respect to the slit and the air flow can be regulated to produce controllable edge tones.

    This demonstration can be finicky, and is sensitive to both careful positioning and to environmental conditions. Try it out before hand.
    H4

    h4-21ch4-21ah4-21b

  • H4-22: BOTTLE BAND

    H4-22
    Demonstrate how edge tones and Helmholtz resonators can be used to create a bottle band.
    This demonstration requires a bass bottle player, three alto bottle players, and a recorder player, but can be rehearsed for a polished performance in a few minutes. The bass bottle player has three notes, while each of the alto bottle players is limited to two notes, so major musical experience is not necessary. The recorder player plays the melody of the song ("Home, Home on the Range" or "Ach du lieber Augustine") while the bottle band vamps.

    Consider inviting students to volunteer in the class period before, then come early to class to try it out. Note that the recorder is also available separately as H4-42.

    H4

  • H4-23: SOUND BOARD - TUNING FORK AND LECTURE TABLE

    H4-23
    Demonstrate the effect of a sounding board.
    If a tuning fork is struck and held in the air, it is not very loud, due to lack of good coupling between the tuning fork and the air. On the other hand, if the bottom of the tuning fork is held firmly in contact with the lecture table or other large surface, it will be much louder. The vibrations are transferred much more efficiently from the tuning fork to the table (the sounding board) and then from the table to the air. Invite students to speculate about the effects of different surfaces in the classroom.
    H4

  • H4-31: VIOLIN

    H4-31
    Demonstrate some acoustical features of the violin.
    Use for show or to play, as desired. Path of vibrations from the string through the bridge, back and belly of the instrument to the air can be discussed. The soundpost and its function can be described. The overtone series can be demonstrated by touching the string at 1/2, 1/3, 1/4, 1/5, 1/6, etc. of the distance from one end while gently bowing.
    OS5

  • H4-32: VIBRAPHONE

    H4-32
    Illustrate how a vibraphone works.
    The vibraphone is an example of transverse standing waves in a bar. Tuning of the bar can be seen by looking at the undersurface. The function of the resonator can be discussed, and the vibration of the sound due to the rotating motorized baffles in the resonator tubes demonstrated.
    FS1

  • H4-33: ORGAN PIPE

    H4-33
    Illustrate how an organ pipe works.
    The pipe can be activated by blowing in the end tube, and the pitch varied by sliding the "closed" end in and out. The end of the shorter tube is open, so it produces a fixed pitch. Pipes of several lengths can be provided.
    H4

  • H4-34: GUITAR AND OSCILLOSCOPE

    H4-34
    Illustrate how a guitar works
    Play notes or chords on the guitar to see their wave shapes on the oscilloscope. Notice that as the notes decay their wave shapes change, a result of different decay times for different harmonics.
    OS5, ME2, ME3

  • H4-35: FRENCH HORN

    H4-35
    Show what a French horn and other similar instruments, such as the French horn, look like.
    This instrument is not in good condition, but is adequate for display in explaining how it works and the function of the valves, etc.
    OS5

  • H4-36: LIP-BLOWN TUBE

    H4-36
    Determine the frequencies and harmonic numbers of the resonances in a plastic tube blown like a trumpet.
    Blowing into the end of the tube as if it were a trumpet creates the odd harmonics. The lip end acts acoustically like a closed end, so in the fundamental mode the tube is one-quarter wavelength long. For this tube, the length is about six feet, so the wavelength of the fundamental is about 24 feet, and its frequency is about 50 Hz. The harmonics are then 150, 250, 350, 450, 550, etc. It is virtually impossible to sound the fundamental, but someone with a bit of finesse with brass instruments can easily demonstrate five or six overtones. Using a tube about 130cm long, seen in the photograph at the right above, the harmonics are odd multiples of 66Hz; this can be heard in an mpeg video with comparison to the frequencies of the overtone series using a Fourier synthesizer by clicking the link below.

    Tubes of different lengths can be made available upon request.
    OS0

  • H4-37: FLEXIBLE TRUMPET

    H4-37
    Demonstrate some acoustical features of the trumpet.
    Adding a trumpet mouthpiece and a funnel to the opposite ends of a flexible plastic tube creates a "flexible trumpet" which has all of the basic acoustical features of the real thing. The overtones are those of a valveless trumpet; like the trumpet, the fundamental is not good on the device. This uses the same mouthpiece as the demonstration Cornet H4-38.
    H4

  • H4-38: CORNET

    H4-38
    Demonstrate the features of a cornet.
    The cornet is virtually identical to the trumpet, except the cornet has a conical bore and the trumpet has a cylindrical bore. This creates a subtle difference in the harmonic structure between the two instruments, but their sound production, tuning, and valve configuration are the same. The cornet can be used to show the geometry and function of the valves, how they are tuned, and the notes produced by blowing the instrument with various valves pressed.
    H4

  • H4-39: PLASTIC TUBE FLUTE

    H4-39
    Show basic features of a very simple flute.
    A "flute" has been constructed using a section of thin-walled plastic. Finger holes have been crudely positioned to obtain a diatonic scale, and the end near the embouchure hole has been covered with tape.

    To get the intonation reasonably close it was necessary to make the holes fairly large, so the flute may be a wee bit difficult to play if you have small fingers.
    H4

  • H4-40: PLASTIC TUBE CLARINET

    H4-40
    Demonstrate how the clarinet overblows at a musical twelfth.

    This clarinet consists of a thin-walled plastic tube into which a clarinet mouthpiece can be inserted at one end. (A real clarinet is available for comparison.) About one-third of the length of the tube from the mouthpiece end is a hole (indicated by the red arrow, about one inch below the thumb in the photograph at the right) which represents the register hole of the clarinet. Closing the register hole produces a low tone, the fundamental. Opening the register hole produces the third harmonic, a note a musical twelfth (one octave plus a fifth) above the fundamental.

    In an actual clarinet, opening and closing the register hole with your left thumb changes the clarinet register from the Chalameau, or lower register to the clarion, or middle register. Covering or opening the finger holes with your remaining fingers provides the notes of the scale within each register.
    H4

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  • H4-41: DRUM

    H4-41
    Demonstrate a pretty drum.
    This is an Ashiko drum, apparently similar to that pictured with Feynman. Unfortunately or fortunately, as the case may be, this one has a synthetic head. This drumhead is nicely tuned to its resonant cavity. For comparison, we have a beat-up steam-damaged older drum with a compromised resonant cavity, so it does not have as nice a tone.
    OS3

  • H4-42 RECORDER

    H2-42
    Can hear the sounds of a recorder
    This is a soprano recorder that uses German fingering. Show what a recorder looks like, how it sounds, and use it in other demonstrations illustrating the wave shape or the spectrum.
    H4