Online Port Length calculator helps to determine the length port size for sub woofer box design.
Formula:
Port Length (L) = (2.35625 × 104 × D2 × N) / (V × F2) - K × D
Where,D - Diameter of vent
N - Number of ports
V - Volume of box
F - Tuning Frequency
K - End correction factor
L - Vent or Port Length