This is a set of 16 Helmholtz resonators. Made from sections of brass that were spun on a lathe, they are wonderfully light and easy to hold. Helmholtz designed them to demonstrate his theory that all vowel and musical sounds are composed of combinations of simple, pure notes (Helmholtz’s “Theory of Timbre”). He correctly observed that musical sounds, particularly the higher tones, are often perceived as a single mass of sound.
In the second quarter of the 19th century, the French scientist Felix Savart invented this apparatus to demonstrate resonance. It consists of a “bell” (or brass bowl) and a moveable wooden resonator. In the demonstration the bell was activated by being either bowed or struck. As the bell rang, its’ loudness could be increased or diminished by moving the resonator closer or further away. When the sound of the bell became barely audible an effective demonstration was to quickly move the resonator right next to it. The increase in loudness – the 'resonant effect' – was striking.
This set of resonance bars, each with its’ own resonator, can be used in an interesting demonstration. First, because the bars are physically identical, they both have the same resonant frequency. And that sound is strongly amplified by the wooden resonators on which the bars are mounted. In the demonstration, the two instruments are placed some distance apart and the first bar is struck sharply to make a tone. Because the two bars are identical, the second bar will respond to the sound of the first by making the same tone.
Chladni, Ernst Florens Friedrich. 2012. “Chladni Plate Demonstration From The National Museum Of American History”. Smithsonian National Museum of American History. https://youtu.be/KEttRmu2kGk.
In 1894, Olaus Henrici (1840-1918) of London devised a harmonic analyzer for determining the fundamental and harmonic components of complex sound waves. It consists of multiple pulleys and glass spheres, called rolling-sphere integrators, connected to measuring dials. The image of a curve (for example, a phonodeik tracing of a sound wave) is placed under the device. The user moves a mechanical stylus along the curve’s path, tracing out the wave form.
This photograph shows a three-dimensional representation of sound using paper. The spectrum (frequencies from low to high) is represented by an arrangement of single strips of paper, with lower frequencies in the foreground. The changes in the spectrum over time are visible as variations in the profile of the paper strips, if read from left to right. Such paper models were used at the Technische Universität Berlin in the 1960s to represent the sounds of speech (phonetics) and music (acoustics).
This photograph shows a three-dimensional representation of sound using paper. The spectrum (frequencies from low to high) is represented by an arrangement of single strips of paper, with lower frequencies in the foreground. The changes in the spectrum over time are visible as variations in the profile of the paper strips, if read from left to right. Such paper models were used at the Technische Universität Berlin in the 1960s to represent the sounds of speech (phonetics) and music (acoustics).
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