I personally think you will be happy with the results of firing the sub down. I read a book recently about building sub enclosures and it addressed this very question. The sub should only be producing bass, not lyrics. Bass is non directional so it's not really going to get "muffled" so to speak. In fact, I think it would sound better than firing to the back of the seat. If anything, the foam in the seat will definitly negatively affect the bass.
Think about home stereo systems (granted these are different speakers but the principals are the same). A down firing sub sounds a lot better than a side firing sub. And if you had a side firing sub, would you place it directly behind your couch firing into the back of it, heck no, so why would you do that in your car?
Interested to hear what you think about how it sounds and good job on the box, it looks really good.

 

great idea!!!! thats where i wanna put my sub!!!

 

I am very interested in how the box sounds. I am looking to do the same thing. Please keep us updated.

Mike

 

Perfect!!! Please post final measurements

 

Home stereo and car stereo is very different. Sound waves from bass are longer than that of higher freqencies therefore, firing down cuts the waves short of forming a nice sine. When the subs are firing down, in a home theatre setup, it's an port/slot enclosure with a specific length to the floor and the port/slot is facing foreward. Having an enclosed sub downfiring is different, but better than facing foreward.

 

Not to mention that the home theatre subwoofer firing down works well because it is aimed at a flat plane (the floor) with relatively few obstacles. This "reflection" of the sound wave is really a way of amplifying the bass.

In such a tight and irregularly shaped space, the sound wave may bounce all over that little compartment and risk cancelling itself.

Firing down in the stock Z location could work, but it's a crap shoot at best. Let us know how it turned out! We'd all be excited if it works!

Also, sheer curiosity....I'm looking for opinions between having 2 8"s or 1 10" in this car. Anyone heard both?

 

There was one member that installed MBQuart 8s, don't recall who. IMO, I'd go 3 8s instead of 2. Again, IMO. The only bad thing is, with the w7, you'd need a 1000 watt 1 ohm stable amp. Quite pricey, but well worth it. I've looked into running 3 JL 8w7s and an Xtant 1000.1. Went with 10s instead. Enjoy!