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Acoustics

  • 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

  • H4-51: MODULATION - AM AND FM

    H4-51
    Demonstrate AM and FM signal modulation as an introduction to vibrato and tremolo.
    The Pasco Dual Function Generator is used to produce either amplitude modulation or frequency modulation using various combinations of sine, triangular, and square waves. Frequency modulation is pure vibrato and amplitude modulation is pure tremolo; actual vocal vibrato is a combination of pure vibrato and pure tremolo.
    H4, ME2

    h4-51ah4-51b

  • H4-52: SPECTRUM ANALYSIS OF MODULATION

    H4-52
    Compare and analyze the frequency spectra of various modulated sounds such as tremolo, vibrato, and beats.
    Using the Pasco Dual Function Generator, a 1000 Hz sine wave is modulated by a 100 Hz sine wave and the spectrum of the modulated signal displayed using the spectrum analyzer. The photograph at the center shows the original 1000 Hz sine wave and the photograph at the right shows the case where that wave is amplitude modulated by a 100 Hz sine wave, producing a beat-like wave and a spectrum that has two sidebands around the 1000 Hz carrier. Amplitude modulation, frequency modulation, or double sideband modulation (sometimes called balanced modulation, or ring modulation with synthesizers) can be used. Two sine waves can be added together using the Dual Function Generator to produce beats, and the spectrum of the beats obtained and compared with that of double sideband modulation. The waveform is displayed on one trace and the spectrum on the other.

    Try out some frequency combinations ahead of time, then have students predict the results.
    H4, ME2, ME3

    h4-52ah4-52b

  • H4-58: MODULATION - AM RADIO

    H4-58
    Show amplitude modulation in in AM radio signals.
    The amplitude modulated signal from an intermediate stage in the portable radio is viewed using an oscilloscope. You may leave it freely running or you may freeze the trace using the oscilloscope stop button in order to obtain the clearest picture for your particular need. Please turn off radio when done to save battery.

    Please handle with care, as discrete-component radios are hard to come by!
    J2B, ME2, ME3

  • H4-71: AUDIOTAPE 20 MIN - ACOUSTICS FOR THE MUSIC EDUCATOR

    H4-71
    Illustrate some principles of room acoustics as applied to music rehearsal rooms and concert halls.
    This tape includes examples of the effects of sound reflecting or absorbing surfaces, anechoic chambers, and reverberation time. A nice sequence replays a recording made in an anechoic chamber with various reverberation times, to illustrate the effect of the auditorium on the sound of a musical performance. The tape was produced as part of a package aimed at educators who are involved in the design of music rooms and concert halls.
    H4, FS1

    h4-71a

  • H4-91: COMPACT DISC - MULTIMEDIA SOUND

    H4-91
    Demonstration of a number of audio effects and source of a variety of musical instrument and other sounds.
    A large number of sounds and pictures of musical instruments are available on this CD. They can be used simply as illustrative sounds or can be fed into a spectrum analyzer. A complete manual is available with description of available material.

    h4-91a

  • H4-92: AUDIO RECORDING - DIGITAL DOMAIN DEMONSTRATION CD

    H4-92
    Examples of early digital sound reproduction.
    Compact disc with audio system.

  • H4-94: AUDIOTAPE - VOICE OF THE COMPUTER

    H4-94
    First full recording of computer-generated music, including the original Shepard's tones.
    This recording was the first full issue of computer generated music. It includes examples of step-wise rising and falling Shepard's tones, and an electronic music suite using a downward glissando version of Shepard's tones to represent the falling of the atomic bombs on Hiroshima and Nagasaki.

  • H4-96: ELECTRONIC MUSIC WITH SPECTROGRAM

    H4-96
    Show spectrograms of electronic music
    Audio CD contains several tracks of electronic music of various styles. A digital spectrogram of the music can be displayed using Windows Media Player version 9, available on all lecture-demo PCs. Alternatively, the CD can be played on the audio cart.

    To run Media Player 9 in full mode, press CTRL+1. To turn on the spectrogram visualization from the menu bar, select View --> Visualizations --> Bars & Waves --> Bars. Don't be shy about asking for assistance from our helpful staff.

    h4-96b

  • H5-01: EAR MODEL

    H5-01
    Illustrate the parts of the ear, their spatial relationships, and their functions.
    This model nicely shows how the major organs of the ear are physically arranged. The bone chain, the cochlea, and the semicircular canal assembly are removable. The fact that space is three-dimensional leads to the necessity of three orthogonal semicircular canals, which can easily be seen. The interesting parts in the middle and inner ears are shown in the close-up photograph.
    H5

  • H5-02: ANATOMY OF THE EAR - SLIDES AND ATLAS

    H5-02
    Illustrate the anatomy of the ear with actual photogrraphs.
    A large set of medical slides illustrates the detailed structure of the human ear. The ear is actually dissected, with each part photographed as it becomes visible. For some of the internal organs a model is also photographed. The slide set is accompanied by a detailed descriptive atlas.
    H5

  • H5-03: STETHOSCOPE

    H5-03
    Hear with a stethoscope, and to experience the time resolution between the two ears.
    Listen to a heartbeat or breathing with the stethoscope. Gently tap the surface of the tube as you move your hand back and forth along the tube; the time between when the tap arrives at the two ears creates the effect of the sound appearing to move laterally.
    H5

  • H5-11: WAVETEK AND AUDIOCART - FREQUENCY RANGE OF HEARING

    H5-11
    Demonstrate the approximate frequency range of human hearing.
    The audio system has a useful range from below 20 Hz through well above 20 kHz, although it doesn't do well below about 40Hz. Have people raise their hands when they hear the tone to see the hearing range of the group. Note also that, keeping the intensity constant while sweeping from 1 kHz to 10 kHz, people hear the tone as louder around 3-5 kHz because the ear is most sensitive in that frequency range. Invite student discussion of why different people may have slightly different hearing ranges, and how that affects us in everyday life. How can this information be used to improve accessibility and inclusivity?
    FS1

  • H5-12: WAVETEKS AND AUDIO CART - CRITICAL BAND

    H5-12
    Demonstrate the effect of the critical band on the sound of two simultaneous sine waves.
    Set the two oscillators to equal amplitudes and the amplifier in monaural, with one at 500 Hz. Starting at less than 100 Hz, sweep the frequency of the second oscillator slowly past that of the first oscillator. When the two oscillators come within about 20 percent in frequency, a coarseness can be heard. This coarseness arises from the overlap of the critical bands of the two tones. Moving the two frequencies closer creates beats.

    Note that these frequencies are chosen to provide an easily audible demonstration; critical bandwith varies significantly with frequency.

  • H5-13: WAVETEKS AND AUDIOCART - MASKING

    H5-13
    Demonstrate masking.
    The first oscillator, the "masking" tone, is set to a 500 Hz sine wave at medium intensity. The second is to be the "masked" tone, which will be varied in frequency and in intensity. The second tone is easily masked when its frequency is higher and its amplitude lower than the masking tone. Masking occurs very readily when the second tone is up one octave, twice the frequency of the masking tone. Frequencies below the masking tone are not easily masked, even at relatively low amplitudes.

    Masking phenomena are significant in understanding the process of hearing. When analyzing a complex sound, it is notable that masked components can be altered or removed without substantially changing the experience of hearing.

  • H5-15: EFFECT OF HARMONIC CONTENT ON TONE QUALITY

    H5-15
    Illustrate Ohm's Law of Hearing, and to hear the sounds of complex waves produced by the Fourier Synthesizer.
    A Fourier Synthesizer including 12 harmonics with independently adjustable amplitudes and phases is connected to an oscilloscope and loudspeaker. Several relevant demonstrations can be performed using this setup: (1) Produce various wave shapes. Listen to the difference in sound as each harmonic is added while the wave is being synthesized. Compare the sounds of the different wave shapes. (2) Demonstrate that although the wave shape changes when the phase of any of the harmonics is changed, change of phase of harmonics has a negligible effect on the timbre or tone quality. Ohm's Law of Hearing states that the sound of a complex tone is to a great degree independent of the phases of the harmonics. (3) Remove the fundamental from a complex tone - best for the pulse train, which has large-amplitude harmonics. The frequency of the fundamental is still audible due to difference tones created by the non-linear mechanism of the ear. The frequency of a complex wave is due in large part to the combined effect of all of the harmonics, illustrating the "missing fundamental."(4) Demonstrate fundamental tracking by varying the frequency of the synthesizer with the fundamental missing. The ear follows the missing fundamental frequency.
    H5, ME2, ME3

  • H5-16: OHM'S LAW OF HEARING - FOURIER SYNTHESIZER

    H5-16
    Validate Ohm's Law of Hearing for a simple case.
    Form a complex tone from the first and second harmonics, with the amplitude of the second harmonic about half that of the first and a fundamental frequency of about 200-500 Hz. Changing the phase of the second harmonic changes the wave shape but leaves the sound virtually unchanged. This is Ohm's Law of Hearing: That the relative phase of components of a sound is, under normal circumstances, undetectable to our ears. Like Ohm's law of electrical resistance, it is not a universal law of nature, but a description relevant to many common phenomena.

  • H5-17: WAVETEKS AND AUDIO CART - QUALITY BEATS

    H5-17
    Demonstrate second order or quality beats.
    One oscillator is set at about 200-500 Hz sine wave, and the other set to the second harmonic (an octave higher) but with about half the amplitude of the fundamental. If the octave is slightly mistuned, the phase of the second harmonic will be continuously changing with respect to that of the fundamental. The slight change in tone quality or timbre is known as "quality beats" or "second order beats." Inasmuch as quality beats are significant, this experiment provides a counterexample to the general statement of Ohm's Law of Hearing.

  • H5-18: DIFFERENCE FREQUENCIES - AUDIO CART

    H5-18
    Demonstrate difference tones.
    Set the two oscillators to equal amplitudes, with the first oscillator at about 500 Hz. Slowly sweep the frequency of the second oscillator from below 100 Hz to above 500 Hz. For very small frequency differences the two tones fuse, becoming a single tone with beats. When the second frequency is near the second harmonic of the first tone (or vice versa), second order or quality beats will be heard. For arbitrary large differences in frequency difference tones will be heard; the strongest occurs at the frequency difference between the two oscillator frequencies. As the frequency of the second oscillator is changed the frequencies of the difference tones can be easily heard to change.
    FS1, ME3

  • H5-19: SUM AND DIFFERENCE TONES

    H5-19
    Quantitatively demonstrate sum and difference tones.
    Set the two oscillators to equal amplitudes with frequencies of 500Hz and 700 Hz, so that the combination tones are not masked by being related harmonically. When the volume of the system is turned sufficiently high, several difference tones will immediately be heard: 200 Hz, 300 Hz, and 400 Hz. Move the frequency of one of the oscillators back and forth by a small amount to call attention to the difference tones. The extra oscillator and speaker can be set to the difference frequency so that it can be identified by the observer. Sum tones also occur, the best example being at 1200 Hz, but it cannot be heard due to masking by the two louder original tones. However, tuning the extra oscillator to a frequency of 1200 Hz at a low a amplitude will allow it to beat with the sum tone, thus indicating that the sum tone is actually there!
    FS1, ME3