Port Length Calculator

Find the vent length for a ported speaker box.

Box volume

Tuning frequency (Hz)

Port diameter

Port length 18.929

Formula: L = (23562.5 * d^2) / (fb^2 * Vb) - 0.732 * d

Step-by-step with your numbers:

1. Values used:

2. Box volume = 30

3. Tuning frequency = 40 Hz

4. Port diameter = 7

6. Port length = 18.929

Did we solve your problem today?

A bass-reflex port is tuned by its length to boost low frequencies.

The math behind it

L = (23562.5 x d^2) / (tuning^2 x volume) - 0.732 x d, with diameter in cm and volume in litres.

A 30 L box tuned to 40 Hz with a 7 cm port needs about 21 cm of port.

What if the port is too long?

Use a larger diameter or multiple ports to keep it manageable.