as he above said, just flip it around and try EVERY which way! I find with my car (Fold down seat) that facing back is the loudest but rattles the most //content.invisioncic.com/y282845/emoticons/frown.gif.a3531fa0534503350665a1e957861287.gif While facing forward does not rattle...but does not even compair in loudness....
Bass wavelengths are longer than mid and high frequencies so when you are bouncing them off the rear of your car they generally sound louder and deeper. Like the other guys said, if possible, move your box around and see what YOU like the best. One way may sound good inside but not outside and vice versa.