- Murray Campbell
An enclosed volume communicating with the atmosphere through a relatively small aperture or neck. Such a cavity has the property of resonating over a narrow range of frequencies; the frequency of maximum response was derived by the 19th-century acoustician Hermann von Helmholtz, and is known as the Helmholtz resonance frequency.
An everyday example of a Helmholtz resonator is provided by an empty bottle. An increase in the air pressure outside the bottle tends to push the air in the neck further into the bottle. This compresses the air in the main volume of the bottle, resulting in a force tending to push the air back out of the neck. The plug of air in the neck bounces on the main volume, like a weight bouncing on a spring. The natural bouncing frequency is the Helmholtz resonance frequency; a note of the corresponding pitch can be sounded by blowing across the open end of the bottle....