From past experiences I have found that when the subs face up and fire the port towards the rear of an SUV it is USUALLY louder then when both the sub and port face the rear of the vehical. I have also found the opposite to be true in cars. Now I am just a simple enclosure builder...to get more in depth information regarding this topic there are several well regarded enclosure designers on this forum that can help you out. Buck, DC Creations, Mobile Enclosures to name a few.