Not enough room, its in a Volvo s80.. I also have 8's mounted in the deck, so if I could manage to face them up, they would interfere big time.The area I have to work with is 39Wx16Hx14.5D. Im limited to this as the entry to my trunk is very small.
Im planning on firing them into the cab and sealing them off from the trunk like my current setup.
That was why I asked.. Others have answered from here, but yes, you do need more passive cone area than speaker, especially with a driver with a strong motor and as much xmax as your passives, I'd be into 2x SD here for sure The passives are tuned to a specific frequency and area WAY more efficient than a sub would ever hope to be at that frequency. So while your sub might only move 18mm over it's subbass range, when the passive begins to move, the sub's force can move it 30mm+ at that frequency. The only way to combat that is to have more cone area in passives so that your sub wont' push them to suspension limits. 1.5x-2x cone area is enough that won't happen.
Sub forward passives back might not ****, but it's not ideal, especially since you want to seal off the trunk and that wouldn't let the passives output in if you do that. Maybe if you removed the 6x9's, but I've done a similar setup and it worked, once I made sure I had as much area for the bass to get into the cabin. So sealing right in front of the sub cone, but then making your rear deck as acoustically transparent as possible and still giving the air room to get around your box to get to the rear deck in the first place. If you do it that way, I'd fire both passives rearward so at least the 2 of them would be aligned. You could also do sub back and port firing in sealed off. However, the sub would benefit more from the baffle, so I would probably seal the sub off and let the trunk have the passives, it's easier for the lowest frequencies to find a way in... If you plan on a very low tuning anyway, your passives and sub won't be playing much at the same time anyways, it would all be at the very lowest of frequencies where your wavelengths may be long enough to get away with that orientation. If you do that you need to make sure the passives output has a way into the cabin.. I know tuned at 25hz I didn't have ny nulls in response running passives side and forward in a trunk, sub back. Probably one of the smoothest sub response I've ever heard in a car. However it wasn't built to be "loud", it was built with a fairly flat response in mind. To replicate that, you'd do sub back and port forward, and don't seal any of it off. Really no matter what you can't "seal" your trunk of totally, since you need to let whichever speaker fires rear have a way back into the cabin.
Other option obviously, you may have to do a standard port here. It's going to eat into your airspace quite a bit, but that sub doesn't really need all that much airspace. If you want do do passives, the best for the money, IMO, come from
http://www.creativesound.ca/products.php. APR15 The passives were designed by Dan Wiggins who used to own Adire Audio. The dustcaps are a bit ugly, but not nearly as bad as the pic suggests, as the pic is a 10 so it just looks silly. The huge advantage of these is that the dustcap unscrews and the weight is added to the front. You can change tuning without removing anything from the box, even compared to most passives it's a huge step up. Also, since you don't have the weight on the back, you don't have nearly as many clearance issues inside the box. From a functional perspective, it's a HUGE step up all around and they are pretty beefy. 32mm of xmax is right up there with most other companies. TC sounds will give 1/3 more, for 2x the price so you STILL need 2 of them in you case either way, the extra 14mm isnt' really functional in that regard, once you get enough cone area, you won't bottom out either one. Combine that with the front loading weight, for me it's a no brainer. Once you get them tuned where you want you could always add a more standard dust cap on top.