Possible interfearance?

[Lowjacker]

I own a hatchback with a shelf running from the top of the back seat to the bottom of the hatch window. In this deck/shelf I have 4 6x9's mounted. If I place my enclosure under this shelf with the drivers firing upwards toward the 6x9's will the air pressure movement cause interfearance, or worse, for the 6x9's or will 400 watts into the subs not be enough to cause a problem. The distance between the enclosure and the cones on the 6x9's is about 18". I just don't want my system fighting itself even a little. I listen to all types of music and get very little to alot of bass.

Secondary question, will this setup affect the potential of the subs. Firing them toward the back seat is a possibility but with no headliner I was really wanting the upward firing. However if SPL or SQ will be affected I'll go however it's recommended.

Thanx in advance for any help

[helotaxi]

Chances are good that the subs will really f-up the response of the 6x9s. Also if there is no way for the output of the subs to vent into the interior, they will totally butcher the 6x9s.

[Lowjacker]

I could, if needed, cut some small holes in the shelf. This would allow air movement directly into the main cabin of the car. Would this help in both aspects since the air would then have somewhere to go?

[helotaxi]

It might help, but the best thing you could do would be to both vent the bass into the cabin, and either enclose the 6x9s or get rid of them altogether.

[Lowjacker]

So perhaps getting some 6x9 boxes and setting them in the hatch area next to the sub enclosure and completely removing the deck so the subs have free access to the interior would be best. Sounds like a plan. Anybody got any money for 6x9 boxes?