http://www.discountsjungle.com/rocfosrfd12p.html

damn that'* cheap for some Hx2'*!!! These things POUND.

I just bought 2 HX2 RFD2112 for $129 each at sounddomain.com. They have those 10s for $109.95 so that is a good price.

Thats a good price. If they were 15s i would try to get them. DO you know of any good deals on any 15s with the same quality as that series?

http://www.partsexpress.com/pe/pshow...number=299-665
It'* a Kove Armageddon Z series without the Kove nameplate. I've got the 12".
It'* very angry with lotsa power.
RF'* are a food group to these beasties.

can this sub sound good too? how would you rate the sound quality

Depends on your box. Do you already have one or are you looking to buy or make one?
As far as the 15, I honestly don't know. I do know the laws of physics tend to cause overhang on the bigger subs. Hence I got the 12". I've got a sealed ~1cu.ft. box. It'* very articulate and can dig deeper than I will allow it electronically. Can't hurt to try one. That'* a wicked price for that kind of performance. I think they have a 30 day no questions policy as well. Don't quote me on that. Check their site. I do remember seeing it though.

I will be making a custom box. I havent heard about overhang up until now, but wouldnt a good suspension greatly reduce this effect if not eliminate it if it were in the right sized box? In your opinion would it sound better to go with 2 12s with a low Fs? What about resonant engineering'* HC series they are the subs that i was originally considering. Have you heard anything good about them

I would go with the 2 - 12'* in individual sealed boxes. You will get tighter & better sounding bass than you would with the 15.

Never heard of Resonant Engineering. Took a quick peek online, they look decent.
I'm just wondering if your looking for SPL, SQ, or a blend. Probably a blend.
15'* aren't going to have that "tight" sound. Physics don't allow it. The mass of the cone alone is enough, yet folks are looking for stupid power handling. That USUALLY means a big coil with lotsa copper, aluminum, whatever they're using for the conductor on the coil (I would not want a speaker designers job these days). Gotta dissipate that heat.
The suspension compliance can help alot at the loss of efficiency. Enter the motor.
I haven't seen the Dumax on these subs , so I dunno about the BL thru the gap.
I do know that listening to this ONE 12" is very gratifying. I personally wouldn't go with anything other than sealed if you are looking for SQ. That 15" in a ported or bandpass could probably do structural damage to your car with enough power
I'd recommend one 12" for SQ. Two if you're looking for stupid output with a bit of SQ.
Obviously these are my opinions.
Whatever you decide, let me know, maybe I could give you a bit of help designing the box.
I've got some decent software for modeling such things.

Me again.
Lower Fs in a car is redundant. I've measured the bass lift (or whatever you wanna call it) in my 2000 SSEI. It'* ~10db/octave starting at ~90hz.
Check out this link to learn a bit more.
http://www.diysubwoofers.org/caraudio.htm
This is a repost so my wrists are bared for punishment.