god-like Subwoofer

the first one. doubling the power adds 3db. doubling the drivers adds 6db ( i think )

Why do you want 500 watts of bass? I ahve one 12" shiva, in an small room with 200 watts amp, I just use it at half volume and is more than enough...for a proper setup of course

Look at SVS.
http://svsubwoofers.com/

you might have to use a larger enclosure if you use 2 drivers....

You never stated a budget.

I don't know your room acoustics. IMO, for a medium to small room for music, there is no benefit with multiple subs.

I’d get a single, high quality, musical sub.

I second the reccomendation for the svs. SVS simply makes the best bang for buck out there. And yes, you can get two.. I highly reccomend getting 2 if you want that extra punch.

The cylinder ones are the best. I have a pc-plus. When you look at sizes.. consider: The smaller you go, the louder it will be .. but the bigger you go (its in height) the deeper the sub will go. I got the mid-size and somewhat wish i woulda went with the smaller size for more HT punch. The mid-size is great for if you do about 50/50 music/HT . the smallest size is great for mainly home theater (because it peaks at the most common HT subwoofer frequencies).

If you do end up getting two, put them both in a (prefferably) open corner. Placing them accross from each other will cause them to cancel each other out.

www.svsubwoofers.com

Dual 12" will give you more output before you hit the excursion limit. Most properly designed subs will run out of excursion before they hit the power (thermal) limit. Bass reflex (vented, ported, etc.) have an advantage in max output, as long as you run a subsonic filter. Sealed designs are faster and beter damped (better transient response) but typically need eq or feedback to get good extension.


gerG

if i were you i would get a sub with two drivers, but with one of the drivers being active and one being passive. if you were to use a dual active sub in such a small room, it would sound horrible. hell, even my sub with two drivers: one active and one passive, has a hard time not reflecting too much off my small room walls. but having the push pull type of subs totally increases the acuracy of the bass notes...almost two fold over regular ported single driver subs! but two active subs, that's overkill, and it would sound way too boomy!! there's simply not enough room in a small room for the two subs to do their work...they will interact with eachother and cancel eachother out in certain situations. i once heard in a friends room, two subs trying to work together in a small room...man did it sound horrible. you know what, it sounded as if i was in one of those bass freak subwoofer cars...you know those people who only care about rattling the cars next to them at a stop light...that's what it sounded like

princeclassic,
remember just because having two active drivers in a sub doubles the power and therefore increases the db by 3 or whatever, does NOT AT ALL mean it would sound better just because it could go louder. louder hardly ever equates to better. i think if someone should look for any type of subwoofer, that they would NOT pay attention to wattage and db but rather the quality and accuracy of the sub...and how well it integrates with their particular system.

It depends on the setup. It's a little too easy to get signal interaction at low frequencies (comb filtering) with two drivers, so I would recommend one driver. I used to use two Sunfire True Sub Jr.'s for nearfield listening, and it ended up being completely ridiculous. One was plenty. Couldn't say it sounded better, because I had gone through great lengths to get the phase(s) right, but the sweet spot ended up being bigger when I took the second one out (went to one sub).

how about building two seperate subs, each one with a 12"? You could still wire them in parallel for your increased power. Or run one per channel with less power. I think the additional room placement possibilities could help you out.

[edit: added] Of course, like Dusty says, this will create all kinds of room interactions. You mentioned you were really going for slam though anway.