Helmholtz resonance

The principle is widely observable in everyday life, notably when blowing across the top of a bottle, resulting in a resonant tone.

Since its conceptualization in the 19th century, Helmholtz resonance has continued to be a subject of study and application, illustrating the interplay between simple physical systems and complex vibrational phenomena.

Helmholtz described in his 1862 book On the Sensations of Tone an apparatus able to pick out specific frequencies from a complex sound.

The proper tone of the resonator may even be sometimes heard cropping up in the whistling of the wind, the rattling of carriage wheels, the splashing of water."

A set of varied size resonators was sold to be used as discrete acoustic filters for the spectral analysis of complex sounds.

There is also an adjustable type, called a universal resonator, which consists of two cylinders, one inside the other, which can slide in or out to change the volume of the cavity over a continuous range.

This process repeats, with the magnitude of the pressure oscillations increasing and decreasing asymptotically after the sound starts and stops.

The port (the neck of the chamber) is placed in the ear, allowing the experimenter to hear the sound and to determine its loudness.

The resonant mass of air in the chamber is set in motion through the second hole, which is larger and doesn't have a neck.

A gastropod seashell can form a Helmholtz resonator with low Q factor, amplifying many frequencies, resulting in the "sounds of the sea".

It can be shown[3] that the resonant angular frequency is given by: where: For cylindrical or rectangular necks, we have: where: thus: From the definition of mass density (

[8] Helmholtz resonance finds application in internal combustion engines (see Airbox), subwoofers and acoustics.

[11][12] Helmholtz resonators are used in architectural acoustics to reduce undesirable low frequency sounds (standing waves, etc.)

by building a resonator tuned to the problem frequency, and putting absorbing material inside, thereby reducing it.

An ocarina[13] is essentially a Helmholtz resonator where the combined area of the opened finger holes determines the note played by the instrument.