Helmholtz resonators

Hollow glass sphere with a small narrow tube leading outwards to demonstrate acoustic resonances. To excite the fundamental, simply blow through the orifice or strike against the hollow cavity.
Due to the elasticity of the air in the sphere in connection with the inert mass of the air in the small tube, an acoustic resonator with a pronounced natural resonance is obtained. Its frequency depends on the dimensions of the sphere and the small tube. A set of Helmholtz resonators illustrates how different notes combine to create a sound.