I use this one - PORT Size Calculations and Formulas for WOOFER and Subwoofer BOXES

You can check the box for slot port. Never failed me yet.

One thing I will add - I have built and measured the tuning frequency of many boxes. If you build a port 10" wide, you are not going to see it act like it is 5" longer. . .The most additional length I have ever measured vs. calculated is about 2-3 inches depending on the port setup.

At one time I was very confused on slot port calculations, because I had measured a few boxes and they were not correct. Once I figured out that I could not gain more than 2-3 inches from the side wall extending beyond the port wall, it has always worked out. Make sense if you think about it, the idea is that the side wall adds additional friction to the air traveling through the port. As the port gets wider, less % of total air moving through the port is affected.

Brian

I noticed after I posted, this is the same one referenced above by Andy. . .

I use this one - PORT Size Calculations and Formulas for WOOFER and Subwoofer BOXES

You can check the box for slot port. Never failed me yet.

One thing I will add - I have built and measured the tuning frequency of many boxes. If you build a port 10" wide, you are not going to see it act like it is 5" longer. . .The most additional length I have ever measured vs. calculated is about 2-3 inches depending on the port setup.

At one time I was very confused on slot port calculations, because I had measured a few boxes and they were not correct. Once I figured out that I could not gain more than 2-3 inches from the side wall extending beyond the port wall, it has always worked out. Make sense if you think about it, the idea is that the side wall adds additional friction to the air traveling through the port. As the port gets wider, less % of total air moving through the port is affected.

Brian

This is a good one that Brian uses. Because it helps you design the enclosure around the driver like it's supposed to be, not the other way around.