Helmholtz resonators drive radiometer vanes, using tuning forks.

Helmholtz Resonators Drive Vanes, A speaker driven by a signal generator sends a sound of a certain frequency into a Helmholtz Resonator. The resonator is basically a hollow metal sphere with a wide opening at one end, and a narrow opening at the other end. Pressure waves from the speaker are focused onto the vanes mounted on a needle pivot,-causing the vanes to rotate. Note1: There are a number of different size resonators, each tuned to a different frequency. Note2: If you are in a hurry, a tuning fork can be used instead of the speaker and signal generator, however the results are not as pronounced.