Bandpass, Sealed or Other?

Kyle, I am a metal head myself. I have tried a variety of boxes through life and have enjoyed many. A sealed box can work good if you have some good signal processing. If you are trying to get some good boomy low bass like what you would find in Korn or Tool, I would go with a ported box. I don't care for bandpass boxes. They may work like a pro but they always look cheezy to me. A vented enclosure is on average, about 3dB louder than a sealed... maybe more maybe less. They are "boomier" than a sealed. You lose the tight, hard-hitting, impact bass like you would have if you listened to speedmetal in a sealed box. I would recommend one 12 in a ported/vented box for your application.

Isobaric enclosures have no discernable purpose that I have ever read or heard about in my life. They seem to be strictly for cosmetic use. Two woofers working in a push-pull design, using the space of only one woofer. Okay well ifyou only took that alone it would be "cool! this looks neat and works in half the space!" However, for everythign that I have read in my life about enclosure design and woofer applications (and that's alot!), the output is the same as it would if you only had one woofer playing! so why bother with the design? Because its cosmetically appealling to some ppl.

Another thing that could help your sealed enclosure: sometimes "professionally built" is not professionally built. Structurally it could be but what I mean is the thought that goes into the building. I have met boxbuilders who build on the minimum size enclosures! This makes a tiny box, yes but it reduces the output. The smaller the box is, the less its ability is to go low. On the flipside though, the smaller it is, the more power it can take. Ported/vented boxes can utilize less power. They are more efficient with a smaller amp and have a stronger output than a sealed enclosure would on the same amp. Check the enclosure volume and relate it to the spec sheet. Make sure the box is built to what Diamond Audio is calling "optimal spec" instead of the smallest size available.

Hope this helps.

Good advice.  Welcome to the forum, Fosgate3.

Here's a great resource to help you choose an enclosure type, by the way: https://www.diysubwoofers.org/caraudio.htm

Id go ported.

If you have the room build a transmission line style box.

Solid info from fosgate3, nice to hear good advice and like he said here is one of his mentionings. I would head in the direction of 2 subs, if they are within the amps capabilities. Before I chose any sub or box combination I would want to know about the amp and the vehicle. It sounds like you have a one note wonder box, not what you imagined from a Diamond sub. Before you run out and buy new subs, I would build (or have built) a ported spec box for that sub, lets see if we can get it operating as it was designed to.

Why would I choose two subs over 1, generally speaking they can attain a higher spl than a single comparable driver, they usually play deeper, they tend to "smooth out" the bass response over a wider range of frequencies. A one sub system in most cases for most but not all people tend to get overworked on a regular basis, a two sub system does not need to be driven near as hard for the same results (in most cases), they can play to a louder sustained volume level for a longer period of time at a lower overall gain level as compared to the single driver. Now I' not saying that you must do this, this is just from pratical experience, I have also built numerous single sub systems that absolutely leave some dual sub systems in the dust, a reference 10" MB quart sub for example and pretty much any Eclipse aluminum or titanium driver as well. What do I use, a pair of Eclipse aluminum 10" subs in a MR2, ba bam.

"I have also built numerous single sub systems that absolutely leave some dual sub systems in the dust"

You and me both Forbidden.