Calculator Inputs
Example Data Table
| Target f (Hz) | Volume (L) | Port (shape) | Area (cm²) | End conditions | Length (cm) |
|---|---|---|---|---|---|
| 80 | 25 | Circular Ø 8 cm | 50.27 | Inner unflanged, outer flanged | 12.3 |
| 60 | 40 | Rect 12×2 cm | 24.00 | Inner unflanged, outer unflanged | 8.9 |
| 120 | 10 | Custom area | 20.00 | Both flanged | 4.7 |
Examples are illustrative; your values depend on real dimensions and end geometry.
Formula Used
A Helmholtz resonator behaves like a mass–spring system. The air in the neck acts as the moving mass, and the compressed air in the cavity provides the spring. The resonance frequency is:
f = (c / (2π)) · √( A / (V · Leff) )
Solving for effective neck length:
Leff = A / ( V · (2πf / c)2 )
The effective length includes end effects. Physical length is:
L = Leff − ΔL
ΔL = (k1 + k2) · req
req = √(A / π)
- f is target frequency (Hz).
- c is speed of sound (m/s), estimated from temperature.
- A is neck/port cross-sectional area (m²).
- V is cavity volume (m³).
- k coefficients approximate flange/edge geometry.
How to Use This Calculator
- Enter your target resonance frequency in hertz.
- Input cavity volume and choose the correct unit.
- Select a port input method: diameter, rectangle, or area.
- Enter port dimensions using the geometry unit selector.
- Pick inner and outer end conditions for better accuracy.
- Optionally set speed of sound manually for special cases.
- Press Calculate to see results above this form.
- Use CSV or PDF buttons to save the computed values.
Tip: if the port is heavily flared or deeply inset, use custom k values.