What formula is used?

The resonant frequency is f = (c / 2π) × √(A / (V × L_eff)), where c is the speed of sound, A is the neck cross-sectional area, V is the cavity volume, and L_eff is the effective neck length including end correction.

What is the end correction?

The effective neck length is L_eff = L + 1.7 × r, where r is the neck radius. This correction accounts for the added air mass that vibrates just outside the neck opening, and is standard in acoustic engineering.

How do I increase the resonant frequency?

Increase the neck area (larger port diameter), decrease the cavity volume, or shorten the neck length. Any of these raises the resonant frequency.

What is a typical use for a Helmholtz resonator?

The most common everyday example is a ported (bass reflex) loudspeaker enclosure, where the port is the neck and the speaker box is the cavity. The port is tuned to reinforce bass frequencies just below the woofer's natural roll-off.

Does the shape of the cavity matter?

For the basic Helmholtz model, only the total cavity volume matters, not the shape. The formula assumes the cavity dimensions are much smaller than the wavelength at the resonant frequency.

What speed of sound should I use?

At sea level and 20 °C (68 °F) the speed of sound in air is 343 m/s. It rises by about 0.6 m/s per °C. For other gases or elevated temperatures, enter a custom value.

Helmholtz Resonator Calculator

Enter cavity volume, neck length, and neck diameter to calculate the resonant frequency of a Helmholtz resonator.

Resonator Parameters

Cavity Volume

Internal volume of the resonator cavity.

Neck Length (mm)

Physical length of the neck/port tube.

Neck Diameter (mm)

Internal diameter of the neck/port opening.

Speed of Sound (m/s)

343 m/s = dry air at 20 °C. Adjust for temperature or other gases.

Enter parameters on the left and click Calculate.

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Summary

A Helmholtz resonator is an acoustic device consisting of a rigid cavity connected to the outside by a short neck or opening. This calculator applies the standard Helmholtz formula — f = (c / 2π) × √(A / (V × L_eff)) — to compute the resonant frequency given cavity volume, neck cross-sectional area, neck length, and the speed of sound. The effective neck length includes an end correction of 1.7 × neck radius to account for the radiation mass at the opening.

How it works

Enter the cavity volume in cubic centimeters (cm³) or liters.
Enter the neck (port) length in millimeters.
Enter the neck (port) diameter in millimeters — the area is computed automatically.
Select the speed of sound (default 343 m/s for air at 20 °C).
The calculator applies the Helmholtz formula with end correction to display the resonant frequency in Hz.
Click Calculate Frequency or press Enter to recalculate the resonant frequency.

Use cases

Design bass reflex (ported) speaker enclosures tuned to a target frequency.
Calculate Helmholtz absorber dimensions for room acoustic treatment.
Tune automotive intake and exhaust systems for a desired resonance.
Suppress tonal noise in HVAC ducts and industrial silencers.
Verify resonance predictions for physics or acoustics coursework.
Design organ pipe resonators and other musical acoustic chambers.
Prototype noise-cancellation enclosures for machinery housings.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu