I have been thinking about this for a while. I was not too sure as too how to add better sound to my X. and to also do this without sacraficing too much space. I have decided to go with 2 JL Audio 8W3V3 subs. They will be mounted in an enclosure in the trunk that is mounted to the rear deck lid. They will be firing up into the parcel shelf. I will have to dynomat the entire rear parcel shelf so i can prevent as much rattles as possible. I figure i would go with 8" subs for 2 reason: 1- they are a good size so i can still keep most of my trunk space, 2- they are large enough to give me some decient bass. This will all be done in the next month or so. I will follow up with a complete how too, and lots of pictures.
I have attach a 3D file so everyone gets the idea. Remember the subs will be firing up into the rear deck, hence the reason why i went with an acrylic/plexi type enclosure, so it will all look good when i am done.

 

I just put two 12" Rockford Fosgate P3s in my X. http://www.rockfordfosgate.com/produ...n_US&p_status=
I was actually really surprised by how much room I still have in the trunk. With he sub box in the trunk I was able to fit a large cooler, a duffel bag, two back packs and a pair of shoes in there this past weekend.
I have the box facing the back seats and since it's usually just me and one other passenger at most times I ride with the back seats down to get the best possible sound. The rear deck will rattle a lot so dynomat the **** out of it, and try to find a way to secure any loose pieces that you see.

 

I'm more into sound quality rather than sound pressure. I find that 2 12's (for me) are way to abnoxiously loud. I listen to a wide variety of music so a good SQ sub is essential. I have already pulled the parcel shelf and and used 2nd Skin (http://www.secondskinaudio.com/vibra...lifier-pro.php) both on the trim piece and the structural piece. I will start with the box construction this weekend. Thanks for the advice.