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.
Lord Kelvin’s harmonic synthesizer is basically Henrici’s harmonic analyzer in reverse. Originally designed as a tide predictor in 1873, the system can combine numerous component waves—in some devices, up to 64 separate components—into a single curve. It is based on the earlier pin-and-slot device, which produces simple harmonic motion with the turn of a crank.
In 1862, the German scientist Herman Helmholtz invented another important acoustic instrument, the double siren. The new instrument combined two Dove Sirens, which were positioned to face each other and coupled on the same shaft. Both sirens were also connected to the same air supply, which made it possible to produce a variety of frequencies, all of which would slide up or down the scale as the air pressure was increased or decreased.
The Smithsonian's National Museum of American History houses literally millions of objects which preserve and illustrate our nation's rich history. Among the many stories that these objects tell are the ways that Americans have learned about science. This site is designed to help students and teachers explore a unique and beautiful collection of instruments used to teach Acoustics - the science of sound. These historic instruments were designed to be engaging and to challenge students to think in new ways about the physical world.