Down fire sub enclosure?

I'm getting ready to purchase a new audio system for my 2016 AC. I have the utility package which deletes the rear seats. I want to do two 8's in a down fire enclosure but have a couple questions.

My plan is for the subs to sit in the rear foot area and have a solid top that goes all the way across tying the two boxes together at the same height as the storage bins. It would give me sort of a platform in the rear.

My question is how small of an opening can I get away with on the bottom of the enclosure and still allow the subs to do their job? Also how many sides need to be opened? Can I get away with just the front of the box facing the front seat to be open? Suggestions?

 

A down firing box will be fine.

I would just build "legs" in each corner of the box.
Something like this.

 

Thanks, I hadn't even thought of doing that.

I don't want to limit myself to shallow mount subs so can anyone tell me if it hurts the performance of the sub if the magnet is somewhat close to the back of the box? I'm looking at around 1.5" of clearance behind the magnet. Does it matter as long as the internal square footage is correct for the sub?

 

Sound quality should not change based on how far the back of the sub is from the enclosure. You just need to avoid mechanical limitations. Alpine type r might be a good choice.

 

If you have a pole vent then yes, it matters. However, 1.5" should be sufficient. If your sub has no rear vent, then you can mount flush against the back wall if you wish.

 

Thanks for the info.

Again, I'm new to this so can you tell me if this sub has a pole vent? I'm assuming yes but it shouldn't matter with me having clearance.

http://www.rockfordfosgate.com/products/details/p2d4-8

 

If there is a hole in the back of the motor that goes somewhere, there is a vent

This one has a vent and needs space between the motor and rear of the enclosure



This one is not vented through the rear and can sit flush against the rear wall of the enclosure



So yes, the sub you're considering has a pole vent. Maybe consider the Alpine Type R 8"? It has a solid back plate. The 10" SD3 pictured above is a good choice for small shallow enclosures as well. I use one.