When ordering this sub you can choose between D4 and D2 whats the difference ?

And im looking at some enclosures, how do you know how much Fb there is in your box, what criterias sets the Fb ?

D2 and D4 refer to the voice coil configuration. You are going to want to pick the configuration according to the amp you have. You can wire the D2 su bwoofer to either 1ohm or 4ohm. The D4 can be wired to either a 2ohm load or an 8ohm load. So telling us what amp you have will let us know which VC you will want.

I'll have to let someone else answer the second part of your question.

The RL-p12 is currently only available in dual 2 ohm coil configuration through our website. We have however produced many dual 4 ohm RL-p12's as well, so there is a chance you could find a used one somewhere. At this time, I do not have a reliable estimate as to the future availability of new RL-p12's in the D4 configuration.

The Fb is the tuning frequency of a ported enclosure. It is determined by the relationship between the enclosure's net volume, port area and port length. For more information on designing a enclosure, I encourage you to check out the following links:

• General Enclosure Information
  http://www.bcae1.com/spboxnew2.htm
  
• JL's Ports Tutorial:
  http://mobile.jlaudio.com/support_pages.php?page_id=165
  
• CarStereo's Vent Length calculator (to avoid that nasty formula)
  Ignore the Vent Diameter calculator and use 20 - 25 inches for the RL-p12.
  http://www.carstereo.com/help2/Articles.cfm?id=31
  
• Some free Generic Box Plans
  http://www.caraudio.com/forum/showthread.php?t=137804
  

THanks for answer, i have another question.

I have chose this 1.85 cu ft net volume vented, Fb = 28 Hz for the box recommended on the site, but does that size include the 0.15 cu ft the sub take ? Or do i make it up to 2 cu ft ?

Sorry for my bad english

I just glanced quickly at it and didn't see anywhere where it took driver displacement into account. So build it to 2.0 ft^3.

My apologies for highjacking bimmer's thread.

I have been thoroughly searching for my next subwoofers, and i've pretty much decided on getting 2 RL-p12 D4. I know you dont have an estimated time, but do you think they might be in stock by the end of the year?

The problem is, my ol' manufacturer declared bankruptcy last December and the new manufacturer has failed to deliver the current order of RL-p18 and RL-i8's for several months now. Until I receive delivery on that order, it would be unwise for me to throw more money into the production side of things. So as you can see, the RL-p12's are not even on order yet, and given that I haven't yet received the previous order, there is really no telling when the RL-p12 D4's will be available again. My apologies for being unable to give you a reliable estimate, but in all honesty, I would not hold your breath!

There are still a handful of RL-p12 D2's left in stock however!