Originally Posted by marcotheclepto
To design a passive radiator alignment, start with a simple ported alignment using that driver that provides the desired box size and frequency response. Then, use the diameter of your chosen passive radiator as the "port diameter", and use this to calculate the required port length. Work out the volume occupied by this port and then use this to calculate the mass of air occupied by this port. The result is the required mass of the passive radiator. If it is too small, use a larger passive radiator and repeat the calculations.
You shouldn't use the exact PR
size though. Use the cone size. For example, the Sd of the PSI is 823cm^2. Using this calculator - Circle And Sphere Calculator
you can determine this it has a diameter of 32.37091511398834 cm or 12.7444548 inches.
You can also determine the tuning of the enclosure by connecting it to Woofer Tester and running an impedance sweep. The frequency of the peak impedance is the tuning frequency of the enclosure.