Which Car is louder

You figured it out, excellent

Some cars are better for bass than others. Here is the problem. A 45 Hz wave is about 300-inches long, at 1/2-wave its about 150-inches long. The wave cannot fully develope in most vehicles because they are not atleast 150-inches long.

Lets look at my Ranger, Its about 65-inches. That means I have a resonant frequency around 208, 104 and 52 Hz. Not bad now lets look at the problem. A frequency of around 208 Hz and higher can fully develope, anything lower can not.

Now building a box that peaks at 52 Hz helps, but doesnt solve the problem. Bass Boost helps (My Kenwood amp boosts at 90, close enough to 104) but again it does not solve the problem.

Have you ever been in a truck, system cranked, windows rolled up and the doors closed. Then you open the door and it gets much louder. All of a sudden the wave has more room.

A wall always works but we are working with a completely different set of rules. We determine the resonant frequency by placing the wall where we want it.

Downfire seems to work well in a truck, why, the wave has a little more room. The problem is that most down fire boxes are too small to be really effective. Trucks are not as good as SUV's. SUV's are not as good as some hatchback cars. Small SUV's tend to be better than large SUV's.

By the way, 1/2 wave resonant is usually better than 1/4 wave. So in your application, you would wanna work with the 60 Hz not the 30. So build something that peaks in the 50 to 55 Hz range. The performance would be quite good.
Hope this helps

 

If I were going for SPL, I would go for 4 cu ft and tune to 38-40 Hz. That should give me a little more peak.