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Helmholtz resonance
Estimate the ideal resonance of a cavity and a single port with a known effective acoustic length.
Cavity volume (L): 0.1–10000; Port cross-sectional area (cm²): 0.1–10000; Effective port length (cm): 0.1–1000
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Helmholtz resonance
Cavity volume (L): 50 Port cross-sectional area (cm²): 50 Effective port length (cm): 10
- Estimated resonance (Hz)
- 54.590145
- Oscillation period (ms)
- 18.318325
Use f = 343 / (2π) × √[A / (V × Leff)] and period = 1000 / f. Convert litres to m³ by ×0.001, cm² to m² by ×0.0001 and cm to m by ×0.01. Enter volume 0.1–10,000 L, port area 0.1–10,000 cm² and effective length 0.1–1000 cm; fractions are allowed. Leff must already include geometry-dependent end corrections, not just physical tube length. The fixed sound speed is 343 m/s, representative of air near 20°C. This lumped, small-signal model assumes a rigid sealed cavity except for one port, with dimensions small compared with wavelength. It excludes damping, leakage, absorption, flexible panels, driver coupling, multiple ports and nonlinear flow. Numerical bounds do not certify that those assumptions hold. This is an ideal resonance estimate, not a loudspeaker alignment, absorber bandwidth prediction or construction specification. Verify geometry and measure the actual response. Display uses six decimals without intermediate rounding.
Methodology
How it works
Use f = 343 / (2π) × √[A / (V × Leff)] and period = 1000 / f. Convert litres to m³ by ×0.001, cm² to m² by ×0.0001 and cm to m by ×0.01. Enter volume 0.1–10,000 L, port area 0.1–10,000 cm² and effective length 0.1–1000 cm; fractions are allowed. Leff must already include geometry-dependent end corrections, not just physical tube length. The fixed sound speed is 343 m/s, representative of air near 20°C. This lumped, small-signal model assumes a rigid sealed cavity except for one port, with dimensions small compared with wavelength. It excludes damping, leakage, absorption, flexible panels, driver coupling, multiple ports and nonlinear flow. Numerical bounds do not certify that those assumptions hold. This is an ideal resonance estimate, not a loudspeaker alignment, absorber bandwidth prediction or construction specification. Verify geometry and measure the actual response. Display uses six decimals without intermediate rounding.
Method and assumptions documented by Techrider.live
2026-11-02
Frequently asked questions
Can I enter the physical port length directly?
Only if it already represents the effective acoustic length. Air near both openings also moves; the needed end correction depends on geometry. This tool does not infer that correction or design a port.