box designer

Hey i have been tryin to use WinISD and the software doesnt make alot of sense to me.  I was modeling 2 audioque HDC3 15's. I put in all the TS parameters and the optimum box it kept putting out was Around 5 cubic foot.  I had fiqured on around a 9 cube ft box tuned to 38hz but it wants a 5 with 46hz tune.  Is this really the best box design for these speakers? 

Also in a tahoe would doing an upwards firing system with ports to the hatch of the suv give a better output or does the conventional everything facing back achieve optimum out put?

Thanks

Wade

In my Navi i tried up and back. Firing rear it actually sounds way better and is was almost 3 DB louder. I have about 18 inchs from the subs to the rear wall. So it allows time for the standing wave to build before being sent forward. The best advice i can give is just do some trial and error. Because what worked for me may not work for you. If you dont have room for the standing wave to build before being sent forward you may be better off facing them up. I noticed in mine facing rear but with it only about 6-8 inched away from the back wall it is not nearly as loud or clear so facing up and porting rear would be better if i had less room. Hope this helps