Use any supported units. Only the fields needed by the selected calculation mode are required.
These worked examples use the same governing equation as the calculator.
| Application | Neck Diameter | Neck Length | Cavity Volume | Temperature | End Correction | Estimated Frequency |
|---|---|---|---|---|---|---|
| Compact speaker enclosure | 40 mm | 50 mm | 2.5 L | 20 °C | Both ends unflanged | 133.7 Hz |
| Small bench resonator | 25 mm | 30 mm | 0.75 L | 20 °C | One end flanged | 201.3 Hz |
| Large acoustic box | 60 mm | 70 mm | 12 L | 25 °C | Both ends flanged | 82.21 Hz |
f = (c / 2π) × √(A / (V × Leff))
A = πr²Leff = L + k × r
f is resonance frequency in hertz, c is speed of sound in meters per second, A is neck cross-sectional area, V is cavity volume, L is physical neck length, r is neck inner radius, and k is the selected end correction factor.
The calculator also rearranges the same equation to solve for required cavity volume, physical neck length, or neck diameter. End correction is included because the air plug extends beyond the visible tube ends and affects the effective acoustic length.
- Select the calculation mode that matches your design goal.
- Enter air temperature, or add a manual sound speed override.
- Choose the end correction model that best matches your tube boundary condition.
- Fill the required dimensions using any supported units.
- Click the calculate button to show the result above the form.
- Review the summary table, design note, and Plotly sensitivity graph.
- Export the result using the CSV or PDF buttons.
- Use the example table to compare your geometry with typical cases.
1) What does this calculator estimate?
It estimates Helmholtz resonator tuning using neck diameter, neck length, cavity volume, sound speed, and end correction. It can also solve backward for missing design values.
2) Why is end correction included?
Air motion extends slightly beyond the physical tube. That extra oscillating mass increases effective neck length and lowers the true resonance frequency.
3) Should I enter inner or outer tube diameter?
Use the inner diameter. The resonating air column is set by the internal flow passage, so outer diameter does not define the acoustic neck area.
4) What happens if the calculated neck length is negative?
Your chosen target cannot be reached with the current diameter, cavity volume, and correction model. Increase cavity volume, reduce diameter, or lower the target frequency.
5) Does temperature matter?
Yes. Warmer air raises the speed of sound, which raises tuning slightly. The calculator accounts for this automatically unless you enter a manual speed value.
6) Can I mix units like millimeters and liters?
Yes. The calculator converts all supported inputs internally to SI units, then reports results back in your selected display units.
7) Is the graph a measured response curve?
No. It is a design sensitivity plot that shows how the predicted resonance frequency shifts as physical neck length changes around the current geometry.
8) Is this valid for every real acoustic system?
It is a strong first-pass design tool for small-signal conditions. Real systems may shift due to damping, leaks, wall losses, large amplitudes, or complex shapes.