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PHYS102

  • H5-21: THREE DECIBELS

    H5-21
    Demonstrate the logarithmic nature of dBs
    The decibel scale measures sound pressure level logarithmically against a base value. As such, a doubling of sound intensity (such as by doubling the number of approximately equivalent sound generators) creates a 3 decibel increase. This scale was developed as a result of Weber's Law: that a noticeable difference in a stimulus is an increase in a constant fraction.

    To demonstrate that doubling the sound intensity creates a change of 3 decibels in the sound intensity level: Divide the class in two, ask one half to make some noise (eg clapping), and note the sound intensity level. Then ask the whole class to make the same noise, raising the sound intensity level by 3 dB. For large groups, a camera may be provided to display the sound level meter.
    H5

  • H6-02: VOCAL FORMANTS

    H6-02
    Demonstrate the formant structure of different vocal sounds.
    The microphone signal is input into a TDS scope with a spectrum analyzer board, and the scope displays both the wave shape and spectrum of the input wave. Differences in the formant structure are easily observed for various vowel sounds such as (upper left to lower right) "oo," "aw," "ah," "eh," "i," and "ee."
    H2, ME2, ME3

    h6-02ah6-02gh6-02bh6-02dh6-02hh6-02e

  • H6-03: VOCAL FORMANTS - MODEL

    H6-03
    A model of vocal formants
    This short tube is closed on one end and has a sliding reed inside it, so when it is inverted the reed slides from one end to the other. (The open end is seen in the photograph at the center above, and the closed end is seen in the photograph at the right. As the air passes through the reed it vibrates, producing a fundamental frequency along with a large number of harmonics. When the reed slides toward the closed end "B" (away from the open end "A"), the vibrating air column becomes longer, so the harmonics resonated by the tube become lower in frequency while the fundamental frequency remains nearly the same. As the reed slides toward the open end "A" (away from the closed end "B"), the vibrating air column becomes shorter, so the harmonics resonated by the tube become higher in frequency while the fundamental frequency remains nearly the same.
    H6

    h6-03ah6-03b

  • J4-51: THEREMIN

    J4-51
    Demonstrate the theremin
    A theremin is a musical instrument, invented in the early twentieth century by Russian scientist Dr. Theremin, which uses capacitance to change the pitch and the loudness of the sound. It was popular in dance bands in the first half of the twentieth century, and even used by The Beach Boys in the 1960s. By moving your hands up and down over the triangular capacitor plates on the top of the box, the frequency and loudness of the sound can be varied to produce a musical tune. Perhaps one of the most elegant examples of theremin music is the Rachmaninoff "Vocalise" performed by Clara Rockmore, the most well-known theremin artist ever, with Nadia Reisenberg on the piano. This music is on a CD, The Art of the Theremin, which will be found in our library of CDs in the "MUSIC" section of the demonstration storage.
    J4, ME3