They require absolutely NO guess and check. They are actually easier IME. First step is to download winisd alpha.
link:
http://www.linearteam.dk/?pageid=winisdpro
Next put your driver into winisd alpha, t/s you can find on your own, or contact the company. Click new project, then click new, for new driver. Then click the parameter tab.. Here is the correct order to enter your parameters so it doesn't give you an error, make sure auto calculate is on
1.Enter Mms and Cms which results in Fs being calculated. If Mmm and Cms are not known enter Fs. If Fs and Mmm or Cms are known enter Fs and the other known value.
2.Enter Sd, Bl and Re. This will result in more auto calculations being made, but Qms and Qts will be blank. If Re is not available, go ahead and enter Sd and Bl.
3.Enter either Qms or Rms, whichever is available, generally Qms is available.
4.If Mms and/or Cms were not provided for input, now input Qes. This will cause some other fields to auto calculate.
5.Enter Hc, Hg and Pe if available. These are not required, however Pe (RMS Power Rating) will give a good idea of how much power signal input to model with.
6.Enter the number of voice coils. NOTE: Drivers using dual voice coils may cause the Bl and Re parameters to change when changing the connection wiring from parallel to series. Be sure to monitor these when changing the connection option, but WinISD should automatically change these values properly.
7.Correct Znom (nominal impedance) if needed. Many times this will change to 6 and should be 2 or 4... or the ultimate resistance (in ohms) you intend to run based on the voice coil configuration and your connection setting (parallel or series).
8.Enter Xmax and any other missing parameters if known and continue. DO NOT change any of the blue auto calculations. If they are only slightly different, this is okay. If they are off significantly, contact the manufacturer or vendor of the driver.
Then start a new PR project, it's the last enclosure choice. put the specs for the passive radiator in question into the program. You can usually find those specs as well on the companies website. You'll need their radiating area, FS, CMS, xmax and VAS.
First step once you've started the project, adjust your box volume FIRST, in the box tab.
Then you'll go and click on the PR tab. First change the number of PR's your using to match the number you have. Then check the instructions to see how many grams each weight weighs in your passive kit, and add weight groups of that much. So if it's 45grams, see what 45,90,135,etc each tunes you to. After that, each washer in your kit will weigh so much so you'll know what to add. If 90 grams gave you the tuning you want, then you'd add 2 washers to each passive. Just add whatever weight you think will give you the best response, based on the graphs you want.
Other thing to look at is your passive excursion graph. On the signal tab change how much power your giving the driver to match your amp, then go to the passive excursion graph in the file thing up top. It's one of your graph view options, just above your graph, click where you can change from Tranfer function magnitude and choose cone excursion PR. Make sure the passives stay below their xmax. If they don't, make sure you engage a SSF. I always run a SSF on passives, even if it's just as 20hz to make sure nothing gets into trouble for sure..
In the real world, sometimes tuning is a hair off, but always worry about how it sounds, not exactly what tuning you have. I have heard passives being next to a wall will actually increase your tuning, not lower it like with a slot port. I would think this is because of the wall making the suspension seems stiffer than it is due to the pressure on the cone. However, I've never ran a impedance sweep to test. IME, they seem to tune more or less where winisd says they will, more reliably than ports anyways. If you feel it isn't play low enough or is too boomy, add a weight, if it's play too loud down low or not quite as loud as you want, subtract one. Nice thing about passives is your not stuck with any particular tuning and can adjust easily once it's in the car.