bandpass questions

hey everyone...im new here and i was hoping someone could answer a few questions I have about bandpass enclosures...i bought this dual bandpass box with two 12's (there's a pic of it here)

i was wondering:

1. what the volume of my box was....the specs are :  (H x W x D): 14.5” x  30.5” x 15” .....and the ports are 4 inches in diameter each..... (i think the volume per chamber is roughly 1.2 cubic feet, but im not sure)

2. which bandpass design is better, the type i bought where there are 2 ported compartments or ones where the subs are side by side sharing on ported enclosure, like this:

3. i was also wondering how big of a difference in sound would there be if i replaced the subs in my box with subs that are supposed to be in larger enclosures...for eg a sub that needs about 3.5 cubic feet of room?

Volume in vented enclosures is critical to the mm.  You wouldn't be able to know for sure what the volume of that box is unless you disassembled it and measured, because you have to account for port and driver and bracing displacement.  The second box shown is most likely two separated chambers as well.  There is room shown in that pic for a dividing wall.  Separate chambers is best to go with so that you can allow each driver to function independent of the other.

If a sub needs 3 ft, you give it 3 ft...which means that the term "sound quality" is a non-factor when you put the wrong sub into the wrong box.  In fact, when you buy premade packages of sub/enclosures like you did, you really don't know if that is the best box design you can use with the subs that are mounted in it.  The Dual bandpass you bought is marketed for the indiscriminate consumer.....that is, make it cheap, simple and ready to go.....and make it fit in my car.  It may sound terrible, it may sound okay...you will just have to plop it in and make your own judgement.

If you want to experiment with substituting drivers, you should also experiment with building your own enclosure for them.  I suggest you use what you have here for the time being and get a feel for what it gives you and what it lacks.  That will give you incentive to do the research and make comparisons to find out what would suit you better when time comes to upgrade your system.  Then this Dual bandpass will be intact for you to pass along to someone else starting out.  Cheers.

The box was a cheap box that came with two crappy ultra linear 12 inch subs, the only specs on the subs are: they claim 800 watts peak and 400 watts rms.