I am making a box for 1 audiobahn 10" high excursion woofer. It can handle 450rms, but I'm only pushing 300rms to it. I am looking for mostly spl(its going in my girlfreinds car, and she "just want it REALLY LOUD!!). I have used win isd, and they suggest .9 cu x 35hz. I thought that once I am not pushing full power to it, that I could make the box bigger to compensate for that. Can someone please help me out?