[dantimdad]

I should have been more clear. The box size wasn't the concern.

Putting a speaker box inside a vehicle is like putting it in another box. Doing so changes the tuning due to the amount of air space in the cabin. If the speakers are too large, they pressurize the cabin before reaching full excursion causing ear fatigue and mistuning.

This is why using smaller woofers that don't move as much air can actually sound like they produce more bass.

You can also use cabin gain to your advantage. Using a smaller than optimum box with a bit higher tuning will allow the woofer(s) to handle more power and, when operated at a lower wattage, last longer, distort less and still reach the lower octaves of the spectrum.

Granted, I tend to go for sound quality rather than spl, but, I have designed a lot of systems for spl as well. It's a dance with any vehicle, trucks even more so.

Steven