Where do you purchase your sub ports

Calculating a slot port from a round port is basic math. The length of the port does not change. The area of the port does not change. So the formula for area of a circle is pi * r^2. Convert this figure to l * w = pi *r^2 and you now have the start of your slot port.

So basically you're saying: converting a 9" x 4"dia round port would give you about a 1"x12"x9" (or 3"x4"x9", etc.) slot port? So long as the length matches correctly for the sound wave to form properly for the box size. Looks like I've been making a mountain out of a molehill trying to figure this out before.

Here is the math behind your 4" round port. Here is the forumula again, 3.14 x r^2 or 3.14 x 2^2 ( the diameter is 4", meaning the radius is half the diameter). Now you have a figure to work with of 12.56". You cannot really have too much port face (per say) but too little is a problem and same with too narrow. Going under 2" for example is going to make some noise, thus the 1" x 12" is not that crap hot of an idea. The 3" X4" is fine, 2" x 6" and so on. Any two numbers that when multiplied = yout known area.

When faced with say 60 sq" of port face, this is going to equate to a crapload of round ports, this is where the slot port really shows it's design. It is very easy to construct a single port on these dimensions. (well sometimes, the box I am working on right now needs 90 sq" of port face and space is at a premium right now). It is far easier and takes less space to make a single slot port than it does to try and squeeze multiple round ports to do the same job (unless the cool factor is what you are after).