sorry i dont check this often. see this site:
PORT Size Calculations and Formulas for WOOFER and Subwoofer BOXES
fill in the stuff and stay within 10-20% of the port area number. as stated before kerfs and aeros you can use less port area because they dont cause as much turbulence in the port as your standard L port or round port. turbulence is bad (port noise).
found this on SSA:
Here's what TermPak has to say about it:
"When designing a vent, you should try to keep the vent air velocity
value as low as possible. Otherwise, vent turbulence and other
audible artifacts may be heard.
Ideally, you would use a vent with a very large surface area to
keep the vent air velocity low. This would work because vent air
velocity is directly related to the area of the vent being used.
Unfortunately, the larger the vent area, the longer the vent length
needs to be for a given tuning frequency. In reality, large area
vents usually need to be so long that they’re just not practical.
Because of this, many designers are forced to trade-off vent air
velocity for vent length.
Typically, audiophiles recommend keeping the vent air velocity
below 5% of the speed of sound. This is not very realistic in
autosound installations where enclosure volumes are usually
pretty small. At Wayne Harris Enterprises, we have determined
that a vent air velocity as high as 12% is acceptable for most
installations. With an Aeroport, the vent air velocity can be as high
as 20% without running into significant problems."