box for fosgate 12" subs

I built a box for 2 fosgate 12" subs exactly to the specs that was in the manual that came with them. They are the Power series subs, and I built them with 1 cubic foot per sub. I have built several boxes before, with no problem. These sound like they don't have enough airspace. The person that I built it for is using an older model Zeus 600 watt amp. He had it pushing 2 15" MTX subs before, so I know it is not the amp. I built that box too. He took it to a stereo shop, and they said it looks like it is the right size, but that they always build their boxes bigger than the recommended size for all subs. Any ideas on what is wrong? They are in a sealed box. Thanks, Lewis

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'85 Toy

Is there air escaping from it somehow? Any pictures?

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try polyfil

Did you take into account the volume displacement of the subwoofers themselves? When dealing in small boxes this is an even more critical factor. Do you have another larger box that you can try one of them in to test the theory that the box is too small?

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Thanks for the advice. Yes I accounted for the displacement of the subs. And the box is sealed real tight. I am going to build a larger box and see if it helps. I have never ran into this problem before, but I will try a bigger box and see what happens. Thanks, Lewis

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'85 Toy

Weird, I've never had a problem with my 12" Fosgate woofer and its in a .8-.9cuft box. Its loud as u know what with 400 watts run'n to it. What series sub is it? Mine is an older Punch HE (RFP3812) and its working fine with a smaller box. I've also played Z's and HE2's in smaller boxes w/o problems so I'm kinda baffled that a little under the specs with the air space would cause distortion.

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"Shiny chrome when used in conjunction with bikini models is particularly effective in inducing brain deficit disorder"

02 Jeep Grand Cherokee

Monster System on its way.

They are Rockford Fosgate Power HX2 4 ohm dual voice coil 12" subs, model RFR3112. They are supposed to be in a 1 cubic foot sealed or 1.5 ported box. They have plenty of power and the box IS sealed tight. Thanks for all the info. Any more? Lewis

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'85 Toy

I'd also say try polyfill, it will actually affect the sound waves inside the box and sound like it has more airspace.  I used to have a pair of the older RF XLC's and boy they require way too much air space!  The box I had to build was the size of a coffin in my trunk, I wish I would have known about fiberglass 3 years ago...

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Im a fiberglass whore!!

1 ft3?? thats maybe ok for a 10 sealed(rest assured i know what they say!!!) i am willing to bet i get as much,only lower bass, from an 8" ported in 1ft3,
just as a rule:(as with anything,there are a FEW exeptions,i try to make sure they are limitations!)

8"- 1 ft3
10" - 2 ft3
12" -3.5 ft3
15" - 6 ft3 (min)
this is more for ported,but at least 1/2 the volume for sealed(w/polyfill)
i just try not to waste(a little extream,but i try to get the most out of what i sell/build) my time,or my customer's money on bigger woofers,when i can get MORE out of a smaller woofer done right..
personnally i am more impressed with an 8" that sounds like a 12",then a 15" that sounds like a 10"..

try an aperiodic,it will ;at least; give you lower bass,and still handle power..
now to stir things up..

I am absolutely correct on this one,do ALOT of research b4 you say what you are going to say..

which box has more pressure to handle?

a ported or sealed?

ported of course..

the reason is the same reason that a woofer handles more power in a PROPERLY constructed ported box..by at least 50%,sometimes more;depending..

this is because of the control a port exerts on the woofer.. keeping it from over exerting when driven hard,yes air can get in and out, but we arent dealing with just air like what a vacuum cleaner puts in/out,we are dealing with waves,the port doesnt let out air when it isnt supposed to! ,the same air it let more of into it on the last excursion that didnt need the control..is the same air that causes the pressure to be greater when it should be..
oh well,thats probably beyond boxes 101,but keep it in mind! something to talk about..
be careful about port calculators, make sure you are dealing with calculations for a lined box! unless you have no parallel sides!(HA,you have any idea how much a truly non parallel box should cost?!?!)


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'Stereo' Mike
The Audio CARtist,LLC
9600 Balt. Ave.
College Park,MD 20740
301-474-6260

A ported enclosure does not handle more power than a sealed enclosure. A ported enclosure uses the rear wave of the subwoofer's movement to further increase the output of the enclosure (by a theoretical 3dB). Technically both enclosures will handle the same power if designed correctly but a ported enclosure will not handle nearly as much power below the tuning frequency of the port. Below the tuning frequency the woofer will oscillate violently (unload) and become unstable. Low bass drops off sharply below the port tuning frequency. Basically the woofer is just flapping around. This is why ported enclosures are more complicated to design and less tolerate of fabrication errors. The woofer, enclosure and port all need to work in harmony together or you'll have problems. And no, ported enclosures do not see higher pressures.

Free air subwoofers generally take less power because they are not supported by a true enclosure. There's much less air spring in free air so you can't feed the woofer as much power. That's why they take less power. Not because they're more efficient or a better design. They just can't handle the higher power.

And while I'm shooting down these theories let me go for the aperiodic. They do not provide lower bass. Just the opposite is true which is why you have to use an equalizer to restore the low bass. That's why Autosound 2000 supplied woofer specific active equalization modules with their MemBrain mats. The lack of low bass in an un-equalized aperiodic system is due to the low Q (highly damped) nature of the design.

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i appreciate all of the advice and opinions that i have got from everybody, but i still don't have an answer to my question. does everyone else except me build box's bigger than recommended? i have never done it before, and i have built box's for several years for several different people for several different type subs. this one type (fosgate) is the only ones that have not sounded like i thought they should.  

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'85 Toy

I doubt that many installers build enclosures larger than the recommended size. That's why it's the recommended size. Making them larger "just because" is kinda goofy. That's not to say you can't but just doing it as a matter of habit doesn't make much sense.

Have you tried the enclosure in a different vehicle? What about only hooking up one woofer and see how that sounds?

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i haven't tried either of these yet. the amp he's using is an old zeus by hifonics. he had it hooked up in the same car running 2 mtx 8000 15's, and it sounded great. only problem was he kept blowing the subs. that is why he went to a "better" sub that is supposed to handle more power. i tried to tell him that 2 12's probably won't sound like 2 15's, even if the 12's are a "better" sub, simply due to the pressure difference that the 15's are capable of giving. or that has been my experience through the years. maybe he is just expecting too much out of the 12's?

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'85 Toy

If you think that based on your experience that there is a problem then there probably is. Those are good woofers.

Speaking of Rockford woofers I just got off the phone with their technical support. I was asking for specs on an older woofer. I asked for the recommended enclosure size and then the Theile/Small parameters. The tech told me the recommended enclosure size and then said I wouldn't need the T/S parameters because this woofer is for sealed only. He said that you only need T/S parameters for designing vented boxes. Wow, and this guy is in tech for RF! That's enclosure design 101.

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I don't believe rockford ever made a dual 4 ohm POWER HX2 unless you mean the new T1's or T2'S but maybe yet again i'm wrong I do that often... I had my 2 12" power hx2's in a sealed box about 1-1.25 facing forward with a bd1500 on each one at a 4 ohm load and rocked a whopping 135 db (VERY EXTREAMLY HEAVY SARCASIM) I was totally dissappointed in the enclosure... so i'm selling the subs and upgrading to this years T1'S and going ported!

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i am starting to believe that this sub is very overpriced and overrated based on what i have heard so far. i'm just glad that i didn't buy them myself. i would not be happy with the sound that they put out.

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'85 Toy

Are you totally certain about your wireing??   Check the terminals at the amp with a DMM to see the actual resistance the subs are wired too.   You coulda had a brain fart like im shure almost everyone has, and possibly seriesed where you should have paralleld.

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2003 Chevy Avalanche,Eclipse CD7000,Morel Elate 5,Adire Extremis,Alpine PDX-4.150, 15" TC-3000, 2 Alpine PDX-1.1000, 470Amp HO Alt.