I determined that the cavity under the front passenger seat in my syncro is
almost sealed and could easily be sealed. This means a subwoofer designed
for a 1/2 cubic foot acoustic suspension cabinet could be mounted there,
facing up into the seat. 

I located a suitable Cerwin Vega speaker 8" in Crutchfield and and
contemplating an install.

But there is a technical issue to address first, which is whether there is
sufficient space for the subwoofer output to get out from under the seat.

I notice that there is an opening to the front of 1" x 15" and in the back
an opening of just 9/16" x 15".

So this is a total exit area of just under 5" X 5" for the subwoofer output
to get out of there. My concern is that this is too small a space. The other
place the sound can go is up into the seat, but there is a metal shield
under the seat so the sound can't go up into there very well.

8" woofer fires into 5" exit hole

Any car stereo people can advise on this? 
___________________________________
Derek Drew                           New York, NY
drew@interport.net