I built a 4cuft net box tuned to 38hz for a L7 15 for my brother. The sub is loud inside the truck(ext cab dodge ram) with the windows down. Everything inside the house is rattling and the sub is loud in the house. However, take 5 steps away from the truck and the sub just doesn't seem to be very loud. Why is this? He had 2 old style Type R 10's in a small ported box(not sure of size or tuning) and it was much louder outside the truck than the 1 15. The box is sitting in the middle of his truck with the 15 firing forward between the seats and the port is up.
Could box size and tuning be an issue here? Should he go with a larger box tuned lower? Or, same size box tuned lower? Or, what? His goal is to be loud on the "outside" of the truck.