Greetings -
Large ports will provide more articulate low frequency at the point of resonance. In other words, a tight bass. Large meaning, 5-8 inches in diameter depending on the volume of the cabinet. On a pair of reproduction ALTEC Lansing Capistrano I built, I used two 6" diameter ducts exiting the bottom panel. The down side; the larger diameter port, the longer it must be. The objective it to keep the vent velocity (mach number ) down. At the point of resonance, it doesn't matter where the port is as long as it is not obstructed. A tube port can even be outside of the enclosure, as it does not have to be inside. When calculating port parameters, consider the tube port as a separate physical element in the circuit. For example; if a circuit board layout has been finalized, but later determined that a choke must be added, then make the circuit board larger to accommodate it. The cabinet volume must be increase to accommodate a tube port.
H.F.