i have built the custom sub box for the back of the car i think i used the plans from the sticky anyways i have a kicker comp c12 in the back powered by a sony 800 watt peak amp 340 watt rms and ways the sub can ht the lows pretty good but if there are any rolling punhces in songs or anything like that they arent loud at all nothing compaered to some 10's i have heard byt the way my box is sealed my frined has a set of clarion 10 inch subs in a sealed clarion box they hit the lows and pound anything i can do all suggestions welcome is the solution buy in a 10 inch sub to go with the 12?

thats why you get a set of Rockford Punch subs

Never mix subwoofer sizes. You got 12s, stick with 12s... ya got 10s... Does your Sony amp have a crossover? If so, it should be set to lowpass to filter the high frequencies out. Is the sub a dual or single voice coil? You may have only one of the coils powered or they may be reversed. Also, the kicker comps like a specific size enclosure or volume of air. It should have come with a manual telling you recommended enclosure sizes in cubic feet, sealed or vented. do you know the air volume of the enclosure you built? does it use the entire hatch... that is usually enough air volume for two 12s. measure height x width x length = total volume. then divide by 1728, that will give you your cubic feet

not trying to argue but....NEVER MIX SUB WOOFER Sizes? 10's and 12 aren't that much different. i could see your point if somebody decided to put an 8 inch sub with a 15 incher next to it in the same box. BUt NEVER MIX ANY SUB.????? never say never.
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btw.....if your having trouble you can easily go onto the rockfordfosgate.com website and they have a cubic inch sub box calculator that you can use. its been awhile since i used it.

buy a new amp problem solved sony amps dont push out what they say they do they are over rated. also what is the specs of your sub??? and what is the specs of your box?? if they dont match there is another problem

My apologies, please allow me to clarify... I merely speak from the standpoint of a MECP certified mobile electronics installer, an eleven year veteran in the business earning top rate at both companies I worked for, and eighteen years as an enthusiast in the hobby of autosound and electronics. When I stated to never mix 10s and 12s I neglected to mention "when they share the same volume of air" I assumed Brandon_McKay constructed an enclosure that is comprised of ONE SINGLE CHAMBER... as opposed to an enclosure with a dividing wall making it TWO enclosures in one structure. Physics tells us that when you have two objects of unequal size sharing one space, the larger object will displace more air than the smaller. When these objects are moving you will create a pressure differential that is not equal... In other words the larger speaker moves more air than the smaller and when they are in the same box they will cause distortion. If you construct two seperate enclosures, one for the 12, and another for the 10, then fine, go ahead, if your goal is simply to be loud and you are not concerned with sound quality. Lastly, one of the best sounding systems I ever heard was a 1991 Mercedes 560 SEC that my best friend, his business partner, and I built. The sub enclosure was a single chamber holding two Image Dynamics IDQ12s, and two more enclosures built into the front floorboards, pointing toward the passenger and driver, holding a pair of Dynaudio 7 inch midbass drivers. The vehicle was featured on the cover of Carsound magazine in summer of 2000, as the winner of the QPC challenge, one of the first vehicles to have a fully functional 12 volt computer as the "head unit", full integration of the Clifford Avant Guard alarm and remote start system, which enabled control of all electronic components in the vehicle via TOUCH SCREEN, such as rolling the windows up and down, locking the doors. and starting the car, and a beta version of the first wireless modem... maybe you have seen it?

In my experience, I prefer 10's because I listen to more rock than rap. The 10's have to move a little more to perform at the same volume as a 12, so I find there is the slightest bit more "kick" to it--it sounds more like a mic'ed kick drum than a really loud CD.

This may or may not be entirely correct for car audio. I'm a former musician, and I kinda applied my PA and guitar speaker cabinet theory to my car--it's worked out for me so far.

brandotron....u definitely got a point there!

I'd be interested to hear what thirdgenfcarnut thinks about my theory--he's the professional. I'm just the guy that used to cram a Marshall 412 cabinet into a firebird to get to gigs

You are correct in what you say. I also prefer 10s. I have a single JL Audio 10W3v2 10 inch sub in a sealed cabinet constructed within the recommended specifications laid out by JL. Our thirdgens are easy to get good bass in because of the shape of the interior. It is a natural acoustic amplifier. I recently built a system for a friend in his 2002 BMW 3 series. He wanted a JL Audio 13w7 13 inch sub in a vented enclosure. That had to be the most accurate, detailed, and punchiest bass I had ever heard... right away I wished for the same thing, but we all cannot afford equipment like that. You used your knowledge and skills, successfully applied it to your vehicle, and are satisfied with the results... who can argue with that?

Cool man, thanks for the input! In my experience, it A LOT easier to build and EQ a kickass a house PA than it is to build a car system...so my hat's off to ya!

jl w7 is no joke i have a jl 10 w-7 in a ported to spec box and its incredable.