Vented a.k.a. ported box is the best type for good sound and loudness. Sealed is ideal for limited space applications as they are smaller than ported boxes.
Bandpass is good for basically nothing. They sound like sh!t.
It IS possible to build a bandpass box that sounds good, but nobody does it because they are no better than ported boxes, they just use more space. Also, all of the pre-made bandpass boxes out there are the type that sound like sh!t.
^^Not necessarily true. I have my Fi Q in a 4th order bandpass box I built. Its lounder AND cleaner than when I had it in a 2.5 cube ported box. Size wise, it was only a 1/2" wider, with the same height and depth. If you can find someone to design you a good bandpass box, they can be very nice boxes. I do not know anything about designing them, but I know they work a lot better for some subs than others.
From a build aspect, they are fairly simple. I used precision ports for mine, so it was basically a dual chambered sealed box with precision ports installed. You are correct on the design portion. From what I unerstand they are very difficult to design.
I agree I used a sealed bandpass box for my pair of 1500GTI's it sounded great!! I had a Nissan pickup lonbed that I ported from the bed, most all sub manufactures have all the data on there website. along with charts that show sub performance, the 1500GTI's in the bandpass box was 99db at 20 hrz
