English: A Helmholtz resonator in an experimental tone generator designed by Hermann Helmholtz. The resonator is the cylindrical object (i). Most musical tones are composed of many frequencies, called harmonics. The purpose of this device was to generate a pure tone of one frequency. The electromagnet (b) vibrates the tuning fork (a). The Helmholtz resonator (i) is tuned to the fundamental frequency of the tuning fork, amplifying its sound.