Helmholtz Resonator Calculator

What Is a Helmholtz Resonator?

A Helmholtz resonator is a cavity connected to the outside through a narrow neck. Air in the neck oscillates like a mass on a spring formed by the cavity volume, producing a sharp resonant peak at a predictable frequency.

Resonant Frequency Formula

$$f = \frac{c}{2\pi}\sqrt{\frac{A}{V \cdot L_{\text{eff}}}}$$

$ A $ is the neck cross-section area, $ V $ is the cavity volume, $ c $ is the speed of sound, and $ L_{\text{eff}} $ is the effective neck length including end corrections.

Effective Neck Length

Real openings add acoustic length beyond the physical neck. A common correction is $ L_{\text{eff}} = L + 0.85d $, where $ d $ is the neck diameter. This accounts for radiation from the open end.

Frequently Asked Questions

Where are Helmholtz resonators used?

They appear in exhaust mufflers, speaker ports, wind instrument tone holes, and acoustic panels tuned to absorb specific frequencies.

Why does cavity volume matter?

Larger volume makes the spring softer, lowering resonant frequency for a fixed neck size.

What speed of sound should I use?

343 m/s is a good default for room-temperature air. Use lower values for colder air or the appropriate speed for other gases.

Does neck shape affect the result?

This model assumes a circular neck. Non-circular openings can use an equivalent area but may need extra correction factors.

What units does the calculator expect?

Neck dimensions in millimeters, cavity volume in liters or cubic meters, and speed of sound in meters per second.

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What Is a Helmholtz Resonator?

Resonant Frequency Formula

Effective Neck Length

Frequently Asked Questions

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