Free · Measurement and planning

Round Speaker Port Length Model

Estimate the length of equal round speaker ports from diameter, net box volume, tuning frequency and a supplied end correction.

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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

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Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.

Formula and method

For the worked example, length = 22.13312500.

Port length cm = 23562.5 × diameter cm² × count / (volume liters × frequency Hz²) − end factor × diameter cm.

Worked example

Enter these known values and leave the other values blank.

Number of ports (N)
1
Vent diameter (D)
10 cm
Box volume (V)
50 L
Tuning frequency (F)
40 Hz
End correction factor (k)
0.732
Length of vent/port (L)
22.133 cm

Assumptions and limitations

  • Empirical round-port tuning model with equal ports and net enclosure air volume.
  • A negative modeled length is not a buildable port. End correction depends on termination geometry; account separately for port displacement and construction.
  • Results follow the stated ideal arithmetic model. Display rounding does not change the underlying calculation.
  • Supply sufficient known values and leave the desired quantity blank. Controls retain captured inverse branches and units.
  • The empirical coefficient corresponds to an assumed sound speed of about 344.15 m/s. It is not temperature-adjusted or a port-flow noise model.
  • If a retained lock prevents a reverse calculation, unlock the quantity you want to solve before supplying the known values.

Common questions

What does the worked example demonstrate?

Port length cm = 23562.5 × diameter cm² × count / (volume liters × frequency Hz²) − end factor × diameter cm.

Can I change the measurement units?

Available selectors convert the entered physical quantity. Use compatible units for all related quantities.

Why can a result be blank?

A missing input, invalid denominator or underdetermined relationship cannot provide a unique finite result.

References

Use exact-sign physical domains, exact discrete counts where applicable, and documented model bounds. Source arithmetic is preserved. Integer membership is checked with isInteger, so ordinary, tiny and large fractional counts are rejected even when tolerant floor equality would pass.

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