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Helmholtz Resonator Port Length — result sheet
Estimate the physical port length needed to tune a Helmholtz resonator to a target frequency with an explicit end correction.
Inputs used
Results
Visual chart
Breakdown
Calculation steps
Returned data table
Formula and methodology
Formula: L_eff = A/[V(2πf/c)²], where A = πd²/4; physical port length L = L_eff − correction × d.
The Helmholtz approximation relates cavity volume, port area, effective neck length, and resonance frequency. Because the air at the opening also participates acoustically, the physical port is shorter than the effective length by the entered end correction.
This result follows the calculator's declared inputs, precision, validation boundaries, and model limits.
Input contract
- Target frequency — Hz; minimum 1.0E-6; maximum 100000
- Cavity volume — m³; minimum 1.0E-6; maximum 1000000
- Circular port diameter — m; minimum 1.0E-6; maximum 1000
- Speed of sound — m/s; minimum 1.0E-6; maximum 10000
- End correction — diameters; minimum 0; maximum 10
Worked example
| Input | Value |
|---|---|
| Target frequency | 50 |
| Cavity volume | 0.1 |
| Circular port diameter | 0.1 |
| Speed of sound | 343 |
| End correction | 0.6 |
A 0.1 m³ cavity with a 100 mm port tuned to 50 Hz has an effective length of about 94 mm and a physical length of about 34 mm with a 0.6-diameter correction.
Assumptions and limits
- The cavity is small compared with the acoustic wavelength and the port is represented by a circular, uniform neck.
- The end-correction multiplier is a design assumption that depends on flare, mounting, wall thickness, and whether one or both ends are flanged.
- Losses, damping, leakage, nonlinear excursion, cabinet stuffing, and higher resonances are not modeled; verify the finished enclosure by measurement.
Calculator note
Source and methodology
Use the official WorldCalculate methodology policy for the source, formula, precision, and boundary standards behind this calculator.
Planning estimate, not financial, medical, legal, or professional advice. © WorldCalculate — reuse with attribution. Built and curated by Hassan ALRowaie.
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