Sizing a ported box
A ported (bass-reflex) box uses a tuned vent to extend the low end below what a sealed box of the same size achieves, at the cost of a steeper roll-off and more sensitivity to tuning. The box volume and tuning frequency depend on the driver's compliance (Vas), damping (Qts) and resonance (Fs).
This calculator gives a quick WinISD-style suggested alignment as a starting point. The efficiency bandwidth product(EBP = Fs/Qes) hints at whether a driver prefers a ported (EBP > ~100), sealed (< ~50) or either (in between) box. Once you have the volume and tuning, size the vent with the port length calculator, and model the full response and port velocity in the enclosure designer.
Results are modelled estimates from published (nominal) parameters — verify by measurement. Looking for another calculator? See all tools & calculators.