🍾 Helmholtz Resonator Calculator
Calculate the resonant frequency of a Helmholtz resonator, such as a bottle, box, or speaker port, based on its geometry.
What a Helmholtz resonator is
A Helmholtz resonator is an enclosed volume of air with a narrow opening (neck) that resonates at a specific frequency when air is disturbed, like blowing across a bottle top. The same principle is used in speaker cabinet ports and acoustic treatment.
The formula
Resonant frequency f = (c / 2π) × √(A / (V × Leff)), where c is the speed of sound in air (~343 m/s), A is the neck’s cross-sectional area, V is the cavity volume, and Leff is the neck length plus an end correction (approximately 1.6√(A/π)) that accounts for air moving just outside the neck opening.
This is the standard acoustic Helmholtz resonator formula; real-world resonant frequency can shift slightly with neck shape and cavity geometry.