# ported or sealed on my JBL w12gti mkii



## eviling (Apr 14, 2010)

I have a JBL w12GTI MKII, and I'm planning on doing some finishing work on my system, just to clean it up, going to build an amp rack, and thinking about making a sub box up in the corner. 









what i have now is a 2 cf + ported box, i love this set up but i was just thinking how nice it would be to have that space back :\ plus the challange of building the box  i've never done one, been doing some research.









probobly something like this one 









or more likley something like this 









onviously i'll have to go very deep for this sub, it requires at the bare minimum 10 inches of depth. 











my biggest concerns are first of all, how does this sub sound sealed? i love it ported. i hear it sounds better ported. but i'm on the fence on which way to go, and if i build a box i'll probably change up my plan for the amp rack to maybe a false floor sub box. thoughts ideas would be most helpful


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## Hardwrkr (Jan 18, 2008)

I'd be interested in some input on this as well as I'm considering doing a single 15GTi sealed. JBL's enclosure info shows that these drivers are quite neutered in output when sealed so that might be a deal breaker.Would you be OK with losing a lot of output to save some space?


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## redcalimp5 (Sep 10, 2007)

I've got a single W12GTi mkII in a small sealed box on 500w, and I sounds great to me. I've always ran sealed, and haven't tried ported, but then again, I listed to mostly all kinds of rock and some metal, and a little bit of hip hop when the mood strikes. 

I recently picked up a JL HD 750/1 to run my 12, and I'm also thinking on having a sealed box built to the GTi's spec, and trashing the one it's in right now.


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## TAMUmpower (Jan 29, 2010)

That M3 looks familiar...something I thought to tell you if I didnt mention it in my build thread. On my car the carpet didnt actually sit against the metal of the trunk, it was buldged out to fit an OEM amp. I took and punched in the buldge so that I could make the back mold of my box as far back as possible.

Something to think about since if you are going to put a box in front of it, who cares what the carpet looks like. Also making an extension up the side of the trunk could get you extra volume rather than just moving the sub out farther from the side.


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## eviling (Apr 14, 2010)

Hardwrkr said:


> I'd be interested in some input on this as well as I'm considering doing a single 15GTi sealed. JBL's enclosure info shows that these drivers are quite neutered in output when sealed so that might be a deal breaker.Would you be OK with losing a lot of output to save some space?


yeah, I don't know how much i'm willing to loose because it's already kinda meh in the cabin with out a really punchy song with this sub or any sub for that matter becasue it's a sedan, i do have it slightly ported into the cabin with the rear deck. i have the stock amp out, and that hole was rather large so that helps a bit. :\ i've been told this sub does its best ported, which is why i went with the ported box i have now. I would just like to do a fully finished look :\

I'd love to hear some input from some people who have tried both sealed and ported with these subs.


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## mattyjman (Aug 6, 2009)

i've done both ported and sealed .. it's pretty much what you would expect. ported is louder and sounds better than sealed

unless you did something wrong


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## eviling (Apr 14, 2010)

guess i'll just stay with my big old box


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## mikey7182 (Jan 16, 2008)

eviling said:


> guess i'll just stay with my big old box


Why not glass a vented enclosure into the side? You said you love the challenge of building a new box, so why not give it a try? Remove that carpet backing from the side of the trunk so you can get an idea of how much space you actually have to work with. You can glass out for the depth of the sub, which should bring the enclosure to just about even with the wheel well. Then glass up and over the wheel well, and between it and the rear deck. You should be able to get 2+ feet out of that area in any good-sized trunk. If you don't have enough room for an internal vent, consider an external one. Either way, it would be a cool project.


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## TAMUmpower (Jan 29, 2010)

mattyjman said:


> i've done both ported and sealed .. it's pretty much what you would expect. ported is louder and sounds better than sealed
> 
> unless you did something wrong


I think thats pretty objective considering the amount of transducers there are in existence, vehicles, and box shapes, dimensions, and installs. In the end if he just wants something boom boom loud then yea tune ur port to the frequency you want and go. But I havent heard many ported boxes that had a good frequency response without a lot of processing, but its all what type of sound quality you want to listen to everyday.

As a blanket statement most would say that sealed sounds better than ported, unless you go ask a rapper....

Why dont you just make a wooden sealed enclosure for it for cheap and listen for yourself before you go to the trouble of fiberglass.


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## mattyjman (Aug 6, 2009)

TAMUmpower said:


> I think thats pretty objective considering the amount of transducers there are in existence, vehicles, and box shapes, dimensions, and installs. In the end if he just wants something boom boom loud then yea tune ur port to the frequency you want and go. But I havent heard many ported boxes that had a good frequency response without a lot of processing, but its all what type of sound quality you want to listen to everyday.
> 
> As a blanket statement most would say that sealed sounds better than ported, unless you go ask a rapper....
> 
> Why dont you just make a wooden sealed enclosure for it for cheap and listen for yourself before you go to the trouble of fiberglass.


well, his question was about the w12gti, which i had, and i was able to do an a/b comparison. all things being equal, my statement stands. the op already has a ported box and for him to put all his effort into a sealed box, really wouldn't pay off sound wise. 

just because you haven't heard many ported boxes sound good doesn't mean that they can't. since you are new here, the more you read and learn, the more you find the common "myths" are really dispelled here, "ported boxes not being sq" is one of them. of course, that statement implies that the end user knows how to tune and create a box for his given sub. 

you last suggestion is right on though... build a sealed box real quick to see what the difference is. shouldn't be too hard to whip something up


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## GouRiki (Apr 9, 2010)

You can model the sub in WinISD to figure out how much cubic ft, port length, and what not.

I created a custom ported box with my friend for his JBL w12GTI MKII to replace the sealed box and it did sound much better in the ported. He is much more into audio than I am and it was a night and day difference to him. The output and sq was a great complement to his thesis set up.


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## [email protected] (Nov 7, 2010)

"sound" issues aside, are you going to be willing to give up the additional output? It's hard to sometimes step down in volume when you get used to it...


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## eviling (Apr 14, 2010)

JOey Knapp said:


> "sound" issues aside, are you going to be willing to give up the additional output? It's hard to sometimes step down in volume when you get used to it...


I can feel that because when i went from sealed to ported it was rather large jump. i love the idea of porting the glassed box, but that sounds really tricky :\ i mean i like the crafty idea of the challenges but now you're talking about mathmatics  lol 

just food for thought, i was board so i ran some frequencys out of my sub for ****s and giggles. 

YouTube - W12GTI MKII ported box 30 hz 40hz to 60hz sweep
:surprised:

I'd gladly pay somebody to work me out a design though  or at least come help and guide me through the process. eastern PA\NJ area. allentown area.


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## mikey7182 (Jan 16, 2008)

eviling said:


> i love the idea of porting the glassed box, but that sounds really tricky :\ i mean i like the crafty idea of the challenges but now you're talking about mathmatics  lol


There's nothing tricky about it.  Just use a round port instead of a slot port. My suggestion would be to build your enclosure first, figure out how much volume you actually have to work with by displacing the inside of the enclosure with packing peanuts, then use WinISD (or any other online calculator) to figure out how long your vent needs to be based on its diameter. For example, say you build your enclosure and you fill it with packing peanuts, and figure out it's about 2.25ft^3. The woofer will displace about .15 cubic feet, leaving you with 2.1 cubes net. Now say you want to tune the enclosure to 32hz and you're going to use a 4" diameter round port. With 2.1 cubes net tuned to 32hz using a 4" port, the port will need to be approximately 12.8" long. Essentially, you're building a 2.25ft^3 sealed enclosure (or whatever volume it ends up being), then cutting a 4" hole in it for the vent and having the vent be external from the enclosure. The "math" is pretty straightforward.  Here's one of the more popular online port calculators:

http://www.carstereo.com/help/Articles.cfm?id=31


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## [email protected] (Nov 7, 2010)

^x2.


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## eviling (Apr 14, 2010)

what about the displaced volume of the port? that must be considered open space no? plus won't i get tunnel vibrations :\


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## mattyjman (Aug 6, 2009)

port will only need to be figured if it's IN the box


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## mikey7182 (Jan 16, 2008)

eviling said:


> what about the displaced volume of the port? that must be considered open space no? plus won't i get tunnel vibrations :\


^what Matt said. What are "tunnel vibrations"? If you buy a 4" Precision Port, the piece that comes with it is 12" long, and with some PVC glue it should be one solid piece... then screw it to the enclosure or glue it through from the inside. You shouldn't have any vibration issues.


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## TAMUmpower (Jan 29, 2010)

mattyjman said:


> well, his question was about the w12gti, which i had, and i was able to do an a/b comparison. all things being equal, my statement stands. the op already has a ported box and for him to put all his effort into a sealed box, really wouldn't pay off sound wise.
> 
> just because you haven't heard many ported boxes sound good doesn't mean that they can't. since you are new here, the more you read and learn, the more you find the common "myths" are really dispelled here, "ported boxes not being sq" is one of them. of course, that statement implies that the end user knows how to tune and create a box for his given sub.
> 
> you last suggestion is right on though... build a sealed box real quick to see what the difference is. shouldn't be too hard to whip something up


I'm aware of the stereotype, I should have said that more SQ guys Ive seen find success with sealed setups than ported, all things being equal. However Chris Pates nationals winning Civic here in town is a ported setup, but obviously with processing and the experience of a nationals guy.

If you are not going to have any equalization then I would stay sealed so you naturally have a flatter frequency response.


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## eviling (Apr 14, 2010)

TAMUmpower said:


> I'm aware of the stereotype, I should have said that more SQ guys Ive seen find success with sealed setups than ported, all things being equal. However Chris Pates nationals winning Civic here in town is a ported setup, but obviously with processing and the experience of a nationals guy.
> 
> If you are not going to have any equalization then I would stay sealed so you naturally have a flatter frequency response.


most of us here are running some sort of sound processing my self i have a high end deck with tons of tweaks, so i tune mine pretty well. granted its no ms-8, which is what i plan on getting


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## LBaudio (Jan 9, 2009)

I've done sealed and ported for this driver - I prefer sealed DF (bigger box than factory suggested with Qc of 0,7 - factory suggestion with Qc is 0,85 which is a little too dry for my taste - I like lil more bottom end) as far SQ is concerned, ported has considerable higher output and takes quite a lot of trunk space. Ported will sound good too, but u will need to Eq it a lil bit


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## eviling (Apr 14, 2010)

score, look what i "foound" laying around at a finished job i was doing, and i have plastic, and mdf left over from antoher project, and my buddy has bondo, fiberglass, ressin and all kidns of containers left from a project he did (he built an iron man suit? epic win lol )


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## HCCA (Apr 6, 2007)

I have two of these in a sealed alignment. They are each getting 1100W. So...I guess I am not missing any output. They get pretty loud. But, as they roll off pretty fast in a sealed enclosure, you have to bump up the bottom end with EQ, a lot, to sound good. 

That said, the guy I bought one of them from was right on about everything else. He was always a fan of sealed, but loved these in a ported box. He said that they sounded as good ported as any sealed subs he had heard...but, more output. 

Now, I have heard a LOT of crap ported subs, or some that were just boomy. My most consistent observation, was that they had an obvious dropout below 30 hz. UNLESS....you were talking about a 18, or two 15's ported. Everyting else I've heard seemed to be missing low frequncy information below 30hz. 

So, I'll never port 10's; sealed only. 12's can work, but I notice missing bottom end info, some of the time. And a pair of 15's ported might just do the trick. 

But, I digress.... Eveling, I think that if you build the box according to JBL's specs (2.25 cft w/13.31" x 4" port), you should get some dam fine sound out of them. A glassed box should work, but you need a thick front baffle. It's a heavy sub.


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## eviling (Apr 14, 2010)

HCCA said:


> . It's a heavy sub.


 with my box right now it tops in near 100 lb's.

but thanks for all the info  i'm still gonna give it a shot, and 1100 a peice, is that what you tuned it to, or what your amps are rated to do? because 1100 rms constantly wouldn't emencly loud, especially with 2 O_O not to mention probobly cut the lifespan of this sub in half, i read that somewhere that 5k watt max is only sustainable for a couple mili seconds.


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## mikey7182 (Jan 16, 2008)

eviling said:


> with my box right now it tops in near 100 lb's.
> 
> but thanks for all the info  i'm still gonna give it a shot, and 1100 a peice, is that what you tuned it to, or what your amps are rated to do? because 1100 rms constantly wouldn't emencly loud, especially with 2 O_O not to mention probobly cut the lifespan of this sub in half, i read that somewhere that 5k watt max is only sustainable for a couple mili seconds.


1100w a piece in a sealed alignment isn't much for these subs. Check out the Sealed Transducer Excursion graph on page one of the enclosure manual:

http://www.jbl.com/resources/Brands...nts/en-US/BoxesandParameters/W12GTi_rev_f.pdf

I've run at least 1,100w to a W15GTi in a vented enclosure with no problems. Remember- a sealed enclosure decreases excursion, so it increases power handling. Not a very efficient design, but some people prefer the sound.


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## eviling (Apr 14, 2010)

what were those specs for the tube to get 33 hz? and where would i go about buying those? parts express?

i'm going to build a sealed box and a ported box, see which one i like more  that's the conclusion i came to, but i'll probobly use the ported one and sell the sealed one over at the old monte carlo forums, people would eat that **** up


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## MLS (Nov 13, 2008)

I'm surprised no one is talking about running these infinite baffle. Has anyone tried it? I know it was talked about in some other threads and the consensus was positive.


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## eviling (Apr 14, 2010)

I've heard good things but IB isn't really ideal for my situation. plus i'm not really looking for that.


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## kizz (Jun 22, 2009)

Ib is great for the gti!


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## rexroadj (Oct 31, 2008)

a well designed ported enclosure for that sub will almost be impossible to beat!


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## eviling (Apr 14, 2010)

so the specs on that tube? i rememebr sombody saying something like 11" long and 4" wide baffeled tube.


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## kizz (Jun 22, 2009)

rexroadj said:


> a well designed ported enclosure for that sub will almost be impossible to beat!


in a ported box would it keep the impact that it has in an IB setup? sorry to thread jack, maybe i should pm this question instead


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## eviling (Apr 14, 2010)

kizz said:


> in a ported box would it keep the impact that it has in an IB setup? sorry to thread jack, maybe i should pm this question instead


ported has some seriouse thud, i've yet to hear to it in IB, but here are some videos of my gti











sounds somewhat harsh but that's because of my crummy mic, but you get the picture.


so about that tube? 33 hz?


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## kizz (Jun 22, 2009)

Yup, i got the "picture" no pun intended lol. it does sound pretty good like that. what is your box tuned to?


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## eviling (Apr 14, 2010)

kizz said:


> Yup, i got the "picture" no pun intended lol. it does sound pretty good like that. what is your box tuned to?


33hz if i recall, it's 2.25 cf or something along them lines, its a very good box, i wont lie i bought it, but it's built to specs for the gti. :surprised:


some things i've been looking up, found some parts. which porting should i get? the 2 peice of the 1 peice? the 1 peice seems ideal because it doesn't require screws i can just mount it into box, but the other one i feel would be more sturdy, but i'd have to put blocking behind the screws. 

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=268-330









http://www.parts-express.com/pe/showdetl.cfm?Partnumber=268-338









*or*

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=268-352









some other misc things i've been adding to the bin
http://www.parts-express.com/pe/pshowdetl.cfm?&Partnumber=260-764&scqty=5









http://www.parts-express.com/pe/pshowdetl.cfm?&Partnumber=340-255&scqty=1









http://www.parts-express.com/pe/pshowdetl.cfm?&Partnumber=365-250&scqty=1









http://www.parts-express.com/pe/pshowdetl.cfm?&Partnumber=091-1245&scqty=1


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## kizz (Jun 22, 2009)

I really like the look of those terminals.


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## eviling (Apr 14, 2010)

mikey7182 said:


> There's nothing tricky about it.  Just use a round port instead of a slot port. My suggestion would be to build your enclosure first, figure out how much volume you actually have to work with by displacing the inside of the enclosure with packing peanuts, then use WinISD (or any other online calculator) to figure out how long your vent needs to be based on its diameter. For example, say you build your enclosure and you fill it with packing peanuts, and figure out it's about 2.25ft^3. The woofer will displace about .15 cubic feet, leaving you with 2.1 cubes net. Now say you want to tune the enclosure to 32hz and you're going to use a 4" diameter round port. With 2.1 cubes net tuned to 32hz using a 4" port, the port will need to be approximately 12.8" long. Essentially, you're building a 2.25ft^3 sealed enclosure (or whatever volume it ends up being), then cutting a 4" hole in it for the vent and having the vent be external from the enclosure. The "math" is pretty straightforward.  Here's one of the more popular online port calculators:
> 
> PORT Size Calculations and Formulas for WOOFER and Subwoofer BOXES


if i went with a 6" over a 4" could i make it shorter? because a 12" long tube inside a 2 cf box with a 10" long sub in an enclousre that's oddly shaped is going to be hard to find a good firing spot, and what kind of spacing do i need? does the port placment its self matter?


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## eviling (Apr 14, 2010)

hmm interesting thought here, what IF i went up to the 15" gti and than went sealed? i wonder


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## jblw10gtimk11 (Jan 16, 2011)

i have my xover on my radio and amp at 50hz down so i run sealed. if your into low bass you should get a sealed fo sure. if your going to run ported dont by prefab, have it built. if your going to build your own make sure the box is not a perfect square. perfect square boxes have acoustic noise, even sealed.


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## tornaido_3927 (Nov 23, 2009)

jblw10gtimk11 said:


> i have my xover on my radio and amp at 50hz down so i run sealed. *if your into low bass you should get a sealed fo sure.* if your going to run ported dont by prefab, have it built. if your going to build your own make sure the box is not a perfect square. perfect square boxes have acoustic noise, even sealed.


...Why?? Have you heard a properly designed ported enclosure?

I would advise against what you're saying right here.


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## rexroadj (Oct 31, 2008)

tornaido_3927 said:


> ...Why?? Have you heard a properly designed ported enclosure?
> 
> I would advise against what you're saying right here.


Dont worry, Ray (the op) knows better! There are several things terribly wrong with the statements above.... Why on earth would someone use a lowpass filter on a deck and amp for the same speaker???????? Who would advise a sealed box over ported for low freq??????? 
Sorry pal, (jblw10gtimkII) this is one of many threads that you have posted that has been completely incorrect. I am not saying this to be a jerk but people come on here to learn and people just spouting off things like that is just dangerous! It is clear you are a jbl fan (look around, your not the only one and you have done nothing but hop into every thread around involving jbl (mostly to speak on behalf of the gti subs, which are of course some of the best around) but a lot of the "information" your throwing around is completely false.... Please be more careful with what your throwing out there! But enjoy the site, and welcome to it!


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## jblw10gtimk11 (Jan 16, 2011)

since when have you ever herd of someone using a subsonic filter for a sealed box, almost never. Ive never herd a ported box sound good down super low, and if a ported box is tuned low, at what expense. My sub woofer out on my hu has a xover 30hz-150, or through which is full range. why wouldnt i use the xover on my hu, and on my amp. As for recommending jbl, i believe people were asking what sub to use. Many people overlook, or never herd of jbl, so yah i wanted to throw jbl in the mix. Besides that, what wrong info am i putting out there?


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## trojan fan (Nov 4, 2007)

jblw10gtimk11 said:


> since when have you ever herd of someone using a subsonic filter for a sealed box, almost never. Ive never herd a ported box sound good down super low, and if a ported box is tuned low, at what expense. My sub woofer out on my hu has a xover 30hz-150, or through which is full range. why wouldnt i use the xover on my hu, and on my amp. As for recommending jbl, i believe people were asking what sub to use. Many people overlook, or never herd of jbl, so yah i wanted to throw jbl in the mix. Besides that, what wrong info am i putting out there?




Stick to your snowplowing and gardening, I have read a few of your post with incorrect info....thanks




ps....GO JBL


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## jblw10gtimk11 (Jan 16, 2011)

what incorrect info trojanfag. your the second guy who said, but no one will tell me what i posted wrong. let me know what info i gave that was incorrect and if i was wrong i can learn and fix it. you guys can be pretty rude and discouraging.


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## rexroadj (Oct 31, 2008)

Ok, I have tried to be nice here (believe it or not). #1 putting things out there like "trojanfag" will be a quick way to get your ass booted from here real quick and in a hurry! Granted the comment he made was also uncalled for (imo). 
You stated that you used a 50hz crossover point on your head unit and amp??????? That is one of the dumbest things I have ever heard! Statements like that go a long way to take away any potential credibility you may have had. Then you go on with some jiberish that makes zero sense about xover points between 30-150????? Seriously....what the hell are you trying to say. (just for the record, what midbass are you using that allows for a 50hz xover point anyway??????) 

If you have never heard a ported box that sounds good down real low then my advice to you is to stop typing here and go out and listen to a HELL of a lot more! You can tune low but at what cost???? What cost or trade off would you be referring to? (by the way, if you have your sub lowpassed at 50 this would be an ideal setup for a low tuned ported enclosure!). 
Honestly I dont think you realize that the more you type the less credible and intelligent you come across. (for the record your other posts in the thread about the guy asking if the p1200 was a good deal (not what sub would be better mind you!) were also false, and your last post proved the point that you obviously did not get the point of what I was saying. He would have no need to get the 12" version (since the box he had available would have been to small) after he heard the 10" version in the box (seeing as how that 10" met the cuft req. he had!) and seeing as the 10" has similar to or equal/greater cone area of most 12s! 
The point is if your going to come onto a site full of pretty experienced and knowledgable individuals and spout off some ****, you better be damn accurate with your words. To this point you have not been and thats the reason for the backlash! 
My advice, if you plan on sticking around and repairing some of your invalid beliefs/understanding as you see it, you might want to take a drastically different approach!


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## jblw10gtimk11 (Jan 16, 2011)

ok do you not use your sub out on your head unit. my subout has a xover and can be adjusted from 30hz to 15hz in 10hz intervals. as i said i can bypass the x over and run it through, but why would i do that. matter fact my old hu if you used the sub out you have to choose a frequencywhat whould you do in this position, if you have a xover in your hu for your sub out what would you do. also like i said ive never herd a ported box that will go as low as a sealed box and have good accurate control over the cone while sounding good doing it down to the lowest octave.im not the only 1 who feels the same wayabout ported boxes. its my onion about the ported boxes ive herd. and what im sorry if i was rude, but no one needs to be spoken to like a child and called out like that. pm me if you got a problem. as for my mid bass, i have 2 10 inch old school jbl powers, you know the titanium ones that were 5ohm. there crossed at 100hz. for 100hz up i have 4 kenwood excelon 4x6 speakers.


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## rexroadj (Oct 31, 2008)

WOW, you just keep going....... I am going to throw in my white flag because you just dont get it! 
You keep backtracking from previous statements you made. Did you or did you not say a few posts up that you set your head unit xover and amp xover at 50hz? YES!
Then you go on to say you have a 10" midbass that is xover at 100hz (big difference from 50). You can say YOU have not heard a ported box that sounds as good as your sealed, thats fine. ONCE again this means you have clearly not heard a well designed ported box and you really should because your statements about them vs. ported are about as incorrect as you can get. FACT!
Honestly I have tried to be fair about your comments and hope for the bennefit of the doubt but honestly at this point I would be willing to bet you have extremely limited experience with audio and most things your speaking of are based on speculation and stigma vs. real experience. 
Now lets get back to the OPs thread!!!! (sorry Ray, I got caught up in the foolishness)

I love the 15" idea  (did you ask me for a price on that?)


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## eviling (Apr 14, 2010)

rexroadj said:


> WOW, you just keep going....... I am going to throw in my white flag because you just dont get it!
> You keep backtracking from previous statements you made. Did you or did you not say a few posts up that you set your head unit xover and amp xover at 50hz? YES!
> Then you go on to say you have a 10" midbass that is xover at 100hz (big difference from 50). You can say YOU have not heard a ported box that sounds as good as your sealed, thats fine. ONCE again this means you have clearly not heard a well designed ported box and you really should because your statements about them vs. ported are about as incorrect as you can get. FACT!
> Honestly I have tried to be fair about your comments and hope for the bennefit of the doubt but honestly at this point I would be willing to bet you have extremely limited experience with audio and most things your speaking of are based on speculation and stigma vs. real experience.
> ...


lol i believe you gave me that info, im kinda stuck with ideas, because i ran the messurements yesterday and i dont like the way the enclousre would have to be, for the origonal spot i wanted to mount it. i have to come up with another idea :worried: i'm also going to be doing a false floor, but i need mroe money, i picked up some fiberglass material and a few misc things yesterday, but got snowed out before i could attempt anything anyways. :mean:

but like i mentioned, with the ms-8 added, the bass is stronger, for what ever reason, so i think going sealed won't be to big of a problem, in fact, i have a problem of having to much bass currently. anyways, i think i'm just drop my 12" in a sealed glassed box and call it a day.


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## jblw10gtimk11 (Jan 16, 2011)

What don't you get? iI have 2 jbl w10gtimk11 subs crossed at 50hz down, then i have 2 10 inch old school jbl titanum powers crossed at 100hz down, then i have 4 kenwood excelon 4x6 speakers crossed at 100hz up. it sounds good to me and thats all that matters. as for the box goes, even at jl audios site they say sealed are better at 30hz down. a ported box below 30hz starts to loose cone control and can damage the sub from to much xmax. i like the low bass that you can feel but cant hear, and a ported box cannot hit frequency's that low. so i guess jl audio is wrong to. go yell at them. as for experience in car audio, ive benn installing car audio in friends and familys rides for the past 15 years, with no complaints. matter a fact i installed my dads hifonics odin, and hifonics vulcan amps, with old school orion colbolt subs when i was 15, and ill be 30 this june. i have nothing to prove to you, but only GOD knows.


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## jblw10gtimk11 (Jan 16, 2011)

cant we all just get along like adults, i have no beef with anyone. so lets continue to learn more about car audio, without calling people out, just to say hay your wrong. if im wrong good, i learned something new. this website is about peoples knowledge and opinions. not about gettin on someones case cause i think sealed do a better job at low frequencys. so if i ruffed someones feathers, im sorry. oh and yah i think jbl rocks, and will continue to recommend them. go jbl


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## subwoofery (Nov 9, 2008)

jblw10gtimk11 said:


> What don't you get? iI have 2 jbl w10gtimk11 subs crossed at 50hz down, then i have 2 10 inch old school jbl titanum powers crossed at 100hz down, then i have 4 kenwood excelon 4x6 speakers crossed at 100hz up. it sounds good to me and thats all that matters. as for the box goes, even at jl audios site they say sealed are better at 30hz down. a ported box below 30hz starts to loose cone control and can damage the sub from to much xmax. i like the low bass that you can feel but cant hear, and *a ported box cannot hit frequency's that low*. so i guess jl audio is wrong to. go yell at them. as for experience in car audio, ive benn installing car audio in friends and familys rides for the past 15 years, with no complaints. matter a fact i installed my dads hifonics odin, and hifonics vulcan amps, with old school orion colbolt subs when i was 15, and ill be 30 this june. i have nothing to prove to you, but only GOD knows.


That statement is wrong. It's not because a ported sub unloads below tuning that it can't hit low notes. 
And it's not that JL is wrong either, but their statement is incomplete. What they should have said is: "In a car, sealed is better from 30Hz down ; a ported subwoofer would be too big for that." unless... 

Here's a comparison between 1 sealed W12Gti and 2 vented W12Gti: 
Sealed (Yellow) in 33L with 1000 watts 
Ported (Red) in 40L tuned @ 20Hz with 1000 watts / -6dB cut @ 20Hz wide Q of 1 
Ported (Orange) in 40L tuned @ 20Hz with 1800 watts / -4dB cut @ 25Hz wide Q of 1 
Why did I apply a cut instead of a Highpass/Subsonic is due to the group delay being added with a filter. My Project: click here 









Just to see how much power is needed to reach Xmax. As you can see, the vented (orange) and the sealed (yellow) hit Xmax @ the exact same frequency: 15.85Hz. 
The ported alignments used show clearly that you won't unload until around 16Hz. 
You can see that the both ported alignments will hit the lows (30Hz and below) with less distorsion due to the use of less Xmax for a given SPL. 









SPL view of each enclosures. As you can see, I managed to reproduce pretty much the exact same freq response vented (Red) than the sealed alignment (Yellow). The vented box in orange shows clearly it's ability to play low frequencies much much much better than the sealed box. 
You like to feel the notes you can't hear? Just look at the orange curve 









Usually group delay for ported boxes are bad, it's not due to bad design but mostly due to the filter applied. A highpass filter adds group delay - just physic. Even a sealed alignment which goes down @ a 12dB rate has a natural highpass that adds group delay. 
As you can see, the group delay is exceptional for a ported box. Way below 25ms @ 20Hz. 









Port velocity graph to show that it's good enough. At the SPL level for full output, port noise will be unheard (below 30m/s @ 20Hz). 









And now the cherry on the cake (stupid french saying ), the efficiency of the system. When comparing the Yellow and the Red curve (both 1000 watts) you can see that the ported alignment is very efficient - meaning you won't need to upgrade your alternator or add a battery in the back. 

All this to show you that if you have the space, a ported alignment CAN hit the low as well or better than a sealed alignment - with all the benefits. 
The EQ used is parametric and can be found in a lot of HU nowadays. My CD7000 and CD7200mkII have it. 

Kelvin


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## rexroadj (Oct 31, 2008)

Well as usual......Perfectly stated Kelvin!!!
Thank you for going into more depth then I was willing to... (although I dont think it will matter) and explaining it far better then I could!


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## jblw10gtimk11 (Jan 16, 2011)

OK i admit, im wrong on certain things. 1 thing though, i said before how if you tune a ported box for low frequencies you do this at some expense . well if you look at the first graph you can see that the xmax is much higher for the sub in the ported box compared to the sealed at the same low frequency, but at 20 hz the sub in the ported boxes xmax dropped drastically compared to the sealed. the sealed controls cone xmax better and has a much broader frequency range, where as the ported has peaks and dips in the frequency range, with less cone control= more xmax and distortion below the ports tunning frequency.So the the tradeoff is the ported box tunned to 20hz has a lot of xmax and therefore should be realy loud past 20hz , but when the ported box reaches 20hz, xmax goes done drasticly therefore it should be pretty quiet , and then xmax goes up again drasticly around 50hz. now wouldn't this tell you that the ported box has less control over xmax at low frequencies. i know a ported box is more efficient, and louder. i can see that the ported box is louder even at the low frequencies, but how much more distortion is there with the ported box at low frequencies due to much more xmax compared to the sealed.


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## tornaido_3927 (Nov 23, 2009)

The fact that the xmax doesn't increase linearly does NOT mean that there is less control over the cone or control over the xmax.


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## subwoofery (Nov 9, 2008)

jblw10gtimk11 said:


> OK i admit, im wrong on certain things. 1 thing though, i said before how if you tune a ported box for low frequencies you do this at some expense . well if you look at the first graph you can see that the xmax is much higher for the sub in the ported box compared to the sealed at the same low frequency, but *at 20 hz the sub in the ported boxes xmax dropped drastically compared to the sealed* (that means 2 things, Xmax is not needed as much as the sealed alignment to produce a given SPL, second less Xmax = less distorsion). the sealed controls cone xmax better and has a much broader frequency range, where as the ported has peaks and dips in the frequency range, with *less cone control= more xmax* (that I agree, however if you look carefully, the sealed and ported alignment BOTH hit MAX Xmax @ 15.85Hz - meaning both the sealed and ported alignment are useless below 15.85Hz. The sealed enclosure might still control below 15.85Hz, MIGHT, but it still unloads like a ported enclosure making it useless below 15.85Hz in the above example) *and distortion below the ports tunning frequency* (from 20Hz to 15.85Hz, the ported alignment will have less distorsion than the sealed alignment ; remember? Less Xmax = less distorsion). So the the tradeoff is the ported box tunned to 20hz has a lot of xmax and therefore should be realy loud past 20hz , _*but when the ported box reaches 20hz, xmax goes done drasticly therefore it should be pretty quiet , and then xmax goes up again drasticly around 50hz. now wouldn't this tell you that the ported box has less control over xmax at low frequencies*_ (Ported alignments have 2 impedance spikes, this is why you see Xmax going up and down like that, HOWEVER, that doesn't mean the frequency response will look like the Xmax curve, just look at the SPL graph, frequency response is smooth and nice from 100Hz to 20Hz - that's all that matters). i know a ported box is more efficient, and louder. i can see that the ported box is louder even at the low frequencies, but how much more distortion is there with the ported box at low frequencies due to much more xmax compared to the sealed.


Hope that helps your understanding a bit. I'm pretty new to this ported thing but have learn quite a lot playing with WinISD and building test boxes. 

Unless you're going for space, I see no reason to go with a sealed box for a W12Gti  
Another advantage the ported alignment has over sealed is that you can adjust the applied EQ so that you have more below 30Hz or less - with sealed, you can only cut... 

Kelvin


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## jblw10gtimk11 (Jan 16, 2011)

thanx for not being a prick and go off. i did notice how smoothe the frequency responce was compared to the xmax for the ported, which did throw me off. i still like that from 10hz to 50hz the sealed box only had a difference of a couple mm xmax. whereas the ported box had a difference of 30mm xmax from only 10hz to 20hz, and a 17mm xmax difference from 20hz to 50hz. so i would definitely think the sealed would be way more accurate especially from 10hz to 20 hz. why does the ported boxes xmax jump around and spike as it goes through its frequency range compared to the sealed, and which is better in that aspect?


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## T3mpest (Dec 25, 2005)

jblw10gtimk11 said:


> thanx for not being a prick and go off. i did notice how smoothe the frequency responce was compared to the xmax for the ported, which did throw me off. i still like that from 10hz to 50hz the sealed box only had a difference of a couple mm xmax. whereas the ported box had a difference of 30mm xmax from only 10hz to 20hz, and a 17mm xmax difference from 20hz to 50hz. so i would definitely think the sealed would be way more accurate especially from 10hz to 20 hz. why does the ported boxes xmax jump around and spike as it goes through its frequency range compared to the sealed, and which is better in that aspect?


As a speaker reaches the tuning frequency of the port, teh port begins to add alot of compliance to the speaker. It stops the cone from moving very much. In addition, the port produces output more and more as you approach tuning. At tuning the cone moves the least and the produces it's maximum output. Near tuning distortion will be lowest as a result, especially if you tune low where a sealed speaker has to move alot more. Sealed boxes have to have the cone moving futher and further as the frequency drops to keep SPL. If you tune at 30hz or below, very little music will go below. What you get is extra acoustic effeciency, more headroom, less amp strain, lower distortion etc, etc as everyone has already said.


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## tornaido_3927 (Nov 23, 2009)

jblw10gtimk11 said:


> thanx for not being a prick and go off. *i did notice how smoothe the frequency responce was compared to the xmax for the ported, which did throw me off. i still like that from 10hz to 50hz the sealed box only had a difference of a couple mm xmax. whereas the ported box had a difference of 30mm xmax from only 10hz to 20hz, and a 17mm xmax difference from 20hz to 50hz. so i would definitely think the sealed would be way more accurate especially from 10hz to 20 hz.* why does the ported boxes xmax jump around and spike as it goes through its frequency range compared to the sealed, and which is better in that aspect?


to add to what T3mpest has said, don't be turned off by the fact that the frequency response does not match the xmax of the driver, that is the whole point of a ported box  the xmax (or displacement) used to reach a certain SPL level at a given frequency is not an indication of how accurately it plays, but is a function of how the enclosure affects (or dictates) the FR of the driver, or system, to be specific.

It might be worthwhile to do some searching on this forum and try to find some of the ported vs. sealed threads to find out the benefits of each and why some people will use the two in different systems to achieve a certain goal.. Hope all this is making sense


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## piyush7243 (Sep 9, 2009)

@subwoofery Reviving an old thread. Anyone can help me out with exact Box and Port dimensions for the Ported box for Gti 12" MKII as the numbers given in the thread give different numbers in winisd
Please help


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## GouRiki (Apr 9, 2010)

Maybe someone could design a better enclosure for your car and available power...

But I would go with the JBL spec box, 2.25 cu ft tuned to 30hz. Remember the 2.25 cu ft includes driver and port displacement. That box performed very for my friend. We decided to swap the box over to my car to see the difference (we have the same amp, so same power) and the sub produced more low end than in his car, his car was difficult to reproduce low end and my trunk was bigger than his + possibly a little more distance from the sub and listener. 

The JBL spec boxes seem pretty spot on. I made the spec box for my w15. It was amazing but I swapped it out after awhile because it was too big for what I wanted in my trunk. I'll probably redesign it later and mold it into a side so i have more useable space in my trunk.

Hope that helps. 

I think the only way to get a better box would be trying different ones or having one designed to take into account cabin gain for your specific car but you'd probably have to pay someone to put that much time into designing. Well worth it though. The GTI's are amazing subs.


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## piyush7243 (Sep 9, 2009)

Thanks a lot for the reply.
I will go with jbl spec box.

Any links to exact dimensions or do I have to design it on my own

Sent from my LG-P999 using Tapatalk 2


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## GouRiki (Apr 9, 2010)

I would design it with dimensions to fit your space that result in a total 2.25 cu ft volume, or as close as you can get. Keep in mind with the port to try to keep in one diameter away from any walls, like if you use a 4" port, try to keep it 4" of space around the opening in all directions. Doesn't have to be perfectly 4" but try so the air can move as freely as it wants and it shouldn't be a problem if you're not using a lot of power. 

I know when I was making my 4 cu ft box, it was difficult to keep enough open space around the port because it is a 6" port. I think I only got away with 3" behind it and 5" on all sides.


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## subwoofery (Nov 9, 2008)

piyush7243 said:


> @subwoofery Reviving an old thread. Anyone can help me out with exact Box and Port dimensions for the Ported box for Gti 12" MKII as the numbers given in the thread give different numbers in winisd
> Please help


The JBL suggestion is good but I like to know a few things - maybe we can tweak the box a bit for your application... 

How much space do you have available? 4cuft? 5cuft? More? 
How much power available? 
What are you trying to achieve? Good SQ? SPL? Pure SQ? 
What kind of music do you listen to? 
Do you have some kind of processing to tweak the subwoofer's response? 

Kelvin


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## piyush7243 (Sep 9, 2009)

subwoofery said:


> The JBL suggestion is good but I like to know a few things - maybe we can tweak the box a bit for your application...
> 
> How much space do you have available? 4cuft? 5cuft? More?
> How much power available?
> ...


I have around 3 Cu Feet Available.
Power would be from Alpine PDX-M12 so @1200wrms
I would want Great SQ but want it a bit loud
I listen to hip hopp, jazz and Blues, lot of classical instruments both Indian and western along with special addiction to vocals
I have a P99RS hooked up so processing would not be a problem.


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## piyush7243 (Sep 9, 2009)

Need help. Please....


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## subwoofery (Nov 9, 2008)

Ok, here's what I suggest: 
2.5cuft tuned to 27Hz - vent: really suggest you try and squeeze 2 ports, in order to keep port noise to a minimum
2 port with a length of 34.44" (length is for each port) - yeah I know it's long but there's no free lunch  You might be able to get creative (since the sub is really deep) and make it look nice. External ports work too... 

Processing wise, try -6dB @ 25Hz, -3dB @ 20Hz and a subsonic filter @ 20Hz 6dB/oct slope. 

That'll do it. 

Compared to JBL's enclosure, my suggestion will act closer to the sealed enclosure (freq response wise), while being more power efficient (amp will run cooler). 

Kelvin


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## piyush7243 (Sep 9, 2009)

subwoofery said:


> Ok, here's what I suggest:
> 2.5cuft tuned to 27Hz - vent: really suggest you try and squeeze 2 ports, in order to keep port noise to a minimum
> 2 port with a length of 34.44" (length is for each port) - yeah I know it's long but there's no free lunch  You might be able to get creative (since the sub is really deep) and make it look nice. External ports work too...
> 
> ...


Thanks kelvin for the recommendations.

Looks great but getting 2 ports of this length is going to be tough. We talking about Slot ports right?


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## subwoofery (Nov 9, 2008)

piyush7243 said:


> Thanks kelvin for the recommendations.
> 
> Looks great but getting 2 ports of this length is going to be tough. We talking about Slot ports right?


Slot port can work but make sure you flare both ends... 

Kelvin


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## piyush7243 (Sep 9, 2009)

subwoofery said:


> Slot port can work but make sure you flare both ends...
> 
> Kelvin


A rough sketch would help a lot. Also i can get Round as well as Slot ports. Which one would be better. or we are talking about Square port.


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## subwoofery (Nov 9, 2008)

Slotted: 









Round: 

















Just be creative and make sure you have FLARED ports. 

Kelvin


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## piyush7243 (Sep 9, 2009)

Got everything except designing the box.

Got calculations from Calculators.

For a rect box of WXHXD=20X14.2X20 with Thickness as 0.75 inches will give a Interior volume of 2.51 cu ft.

Single Slot Port
Port Width:2.2"
Port Height:12"
Port length:34.58

For round port
Port Diameter:5.8"
length: 34.67036


How to divide the port dimensions into 2 parts as you have advised to use 2 ports in one enclosure.

Sorry for being a noob here.


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## subwoofery (Nov 9, 2008)

piyush7243 said:


> Got everything except designing the box.
> 
> Got calculations from Calculators.
> 
> ...


If you can fit a 5.8" (6") round port, one is enough. Length is correct too. 
Don't know if my calculations are rusty but the volume of the port seems to be about 2.12cuft so your gross volume needs to be 4.62cuft. 
Using Rockford Fosgate® - RFTECH Support
You can make the box 20" (H) x 12.8" (D) x 40" (W) 
^ ends up to 4.66cuft - should go down with some braces to make the box rigid enough. 
Port above subwoofer on the (D) side 

Don't know your trunk dimensions but this is just to give you an idea... 

Kelvin


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## piyush7243 (Sep 9, 2009)

subwoofery said:


> If you can fit a 5.8" (6") round port, one is enough. Length is correct too.
> Don't know if my calculations are rusty but the volume of the port seems to be about 2.12cuft so your gross volume needs to be 4.62cuft.
> Using Rockford Fosgate® - RFTECH Support
> You can make the box 20" (H) x 12.8" (D) x 40" (W)
> ...


Thanks a lot Kelvin for being so patient with me, i will be working on this. Also i have got a sealed box in the meantime for 1.3 cu ft which will be a little less after Sub fits in and it's great. SPL is not so much but it would do at the moment.

Again thanks a ton


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## Oscar (Jun 20, 2010)

IHMO, it would be much wiser to do a single slot port, but you'd need a lot more than a 12x2.2 port. My W10GTi can really move the air in the 12x3 slot port used, the W12GTi needs the same if not a tad more. The good news is that you can cut the required port length of a slot port 40% if you use 3 enclosure walls as part of the port walls. This extra air-mass coupling lets you tune low WITH a large enough area to keep vent air speed decently low.

My W10GTi box is 1.75 ft³ after displacements, with a 12"x3"x32". Anyone wanna tell me what they _think_ it's tuned to?


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## subwoofery (Nov 9, 2008)

Oscar said:


> IHMO, it would be much wiser to do a single slot port, but you'd need a lot more than a 12x2.2 port. My W10GTi can really move the air in the 12x3 slot port used, the W12GTi needs the same if not a tad more. The good news is that you can cut the required port length of a slot port 40% if you use 3 enclosure walls as part of the port walls. This extra air-mass coupling lets you tune low WITH a large enough area to keep vent air speed decently low.
> 
> My W10GTi box is 1.75 ft³ after displacements, with a 12"x3"x32". Anyone wanna tell me what they _think_ it's tuned to?


I'd like to get more infos on this. Never read anything like it - even on DIYaudio. 

Can you please elaborate on how using 3 enclosure walls will get help in creating extra air-mass coupling --> lowering the tuning for the enclosure... 

Kelvin


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## piyush7243 (Sep 9, 2009)

Oscar said:


> IHMO, it would be much wiser to do a single slot port, but you'd need a lot more than a 12x2.2 port. My W10GTi can really move the air in the 12x3 slot port used, the W12GTi needs the same if not a tad more. The good news is that you can cut the required port length of a slot port 40% if you use 3 enclosure walls as part of the port walls. This extra air-mass coupling lets you tune low WITH a large enough area to keep vent air speed decently low.
> 
> My W10GTi box is 1.75 ft³ after displacements, with a 12"x3"x32". Anyone wanna tell me what they _think_ it's tuned to?


yep. some more info on this one plz. sounds interesting.


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## minbari (Mar 3, 2011)

Oscar said:


> IHMO, it would be much wiser to do a single slot port, but you'd need a lot more than a 12x2.2 port. My W10GTi can really move the air in the 12x3 slot port used, the W12GTi needs the same if not a tad more. The good news is that you can cut the required port length of a slot port 40% if you use 3 enclosure walls as part of the port walls. This extra air-mass coupling lets you tune low WITH a large enough area to keep vent air speed decently low.
> 
> My W10GTi box is 1.75 ft³ after displacements, with a 12"x3"x32". Anyone wanna tell me what they _think_ it's tuned to?


a ports a port. doesnt matter if you use 3 of the walls to make it. which is the whole point of a slot port in the first place. tuning a W10gti to 38 hz is pretty high IMHO


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## ScottyGreen (Apr 3, 2012)

Hopefully this isn't considered "thread jacking" since I'm building an enclosure for the same woofer... the 12" one...

My enclosure is 2.1 after displacement.

Question is this:

*I listen to Rock music and some electronic (NIN, etc)

Should I tune to around 30hz or say maybe 33 or will it matter much?
*
I've been playing with winisd alot and keeping excursion limits in mind...
*I also have a subsonic filter at 28hz on my amp, so I'm trying to let the port/woofer "unload" just below 28hz (which i think is the way to do it, correct me please if I'm wrong)*
help would be appreciated...


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## Oscar (Jun 20, 2010)

minbari said:


> a ports a port. doesnt matter if you use 3 of the walls to make it. which is the whole point of a slot port in the first place. tuning a W10gti to 38 hz is pretty high IMHO


You couldn't be further from the truth. The truth is revealed through emperical data.


This topic is a recent thread started by someone else on DIYAudio.com

Vent dimensions when 3 of 4 sides are the enclosure's wall - Page 2 - diyAudio


Courtesy of another diyaudio member (bjorno):











There's no mystery about it. Even a _standard_ circular port needs an end correction factor that *requires* you to make it just a smidge shorter to achieve your target Fb. IMHO, it's because you just can't "separate" the airmass inside the port from the airmass _immediately_ outside of it. Those of you who know about this know about where this comes from; the equation for port tuning from before there were programs to simulate tuning.

Courtesy of The Subwoofer DIY Page

Lv = (23562.5*Dv^2*Np/(Fb^2*Vb))-(k*Dv)

where,

Dv = port diameter (cm)
Fb = tuning frequency (Hz)
Vb = net volume (litres)
Lv = length of each port (cm)
Np = number of ports
k = end correction (normally 0.732)

The "k" end correction is simply necessary because the calculated length just didn't jive with what was seen (ie: observed) with regards to actual tuning frequencies. I believe that the "slot style" type port merits more end correction (reduction for a given Fb) because it couples more airmass to it's cross sectional opening in a way that is parallel to how slot ports have more perimeter around the mouth than a circular port of the same cross sectional area.

So I'm glad someone came up with the _incorrect_ tuning frequency for my box, because in reality it's tuned _a lot_ lower. Look at this impedance plot for this particular enclosure of mine:











That's right. *31.6** Hz*.

For those who don't believe the port size: (yes, I know it's ugly, but *IDGAF*, this goes in my racecar, not a showcar  )




























Couldn't quite get the right angle on the camera, but you can see the size of the shelf of the port inside the box:



















BTW, the end of the port wall inside the box is a good 5.5" from the end of the back wall, so _no_ extra port length action going on there.


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## Oscar (Jun 20, 2010)

ScottyGreen said:


> Hopefully this isn't considered "thread jacking" since I'm building an enclosure for the same woofer... the 12" one...
> 
> My enclosure is 2.1 after displacement.
> 
> ...


do you know if the subsonic filter is a 12 db/octave or a 24 db/octave slope?

there won't be too much of a difference between 30-33, but for rock music, you won't lose out too much tuned to 33-35. 

If you can find out the slope of the subsonic filter, I can model the predicted free-field response with a more powerful program than WinISD, Akabak.


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## ScottyGreen (Apr 3, 2012)

@Oscar...

That would be greatly appreciated. I'm looking to create some sawdust this evening once it cools off a little!

here is what I found on my amps subsonic filter:
Infrasonic: 12dB/octave Butterworth, -3dB @ 28Hz 

I also have a pioneer deh-80prs so I can play around with 20hz and 31.5hz +or- 6db

I can do 2.1 cu or 2.25 cu after displacement, but 2.25 is the absolute max and would prefer 2.1 even if it makes a tiny bit of compromise somewhere.
Forgot something: my amp is a rockford 1000-1 birthsheet says 1506w rms at 2ohms, since this will be 3ohms I'm guessing around 1100-1200 RMS
I have also noticed that the higher I tune my port velocity rises very rapidly, so I'm looking to stay 33hz or less if possible given my set box size requirements.

Main focus is Rock music with deep kick drum, car size is a sedan a little on the larger size, chrysler 300

Thank you SOOO much for taking this into consideration and running this through your program!

I'll check back after a bit... thx


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## minbari (Mar 3, 2011)

if it is truely putting out 1500 watts at 2ohm, then 3 ohms will be 1000 watts.


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## Oscar (Jun 20, 2010)

ScottyGreen said:


> @Oscar...
> 
> That would be greatly appreciated. I'm looking to create some sawdust this evening once it cools off a little!
> 
> ...


I can help you, but you first have to want to help yourself. What I mean is, how can you know the final displacement if you don't know how much space the port will be taking up? Point is you can't. Now if you mean internal airspace after taking into account bracing and driver displacement, then you have wayy too little space.

Also, one thing you need to grasp, is that tuning is a vicious circle. That is one downfall of playing with programs like WinISD and not realizing what is necessary to implement a particular design. It is true that if you lower tuning for a given vent area, that airspeed will drop, but you fail to realize that to actually achieve that lower tuning, you either have to *A.* Increase port length (which will actually reduce internal box volume so it's counter-productive), or *B.* Reduce vent area while keeping vent length constant (which will raise vent velocity even more).

A good size port (even when taking into account the reduction of using 3-enclosure walls) is going to take up *0.8-1.0 ft³* at your power levels!

What I need to know is this: The 2.5 ft³ that you mentioned. That is internal net volume available? Or is that external dimensions not even taking into account the thickness of the woods (which also happens to account for a lot of space!)?




minbari said:


> if it is truely putting out 1500 watts at 2ohm, then 3 ohms will be 1000 watts.



I get 1125W. I dunno how you got your 1000W @ 3ohms.


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## ScottyGreen (Apr 3, 2012)

@minbari ok, well I got that estimation because at 4ohms the birthsheet says 894w rms, so I just picked kind of a middle point-ish


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## ScottyGreen (Apr 3, 2012)

@oscar 

Heres how I arrived at my numbers so far...
I understand I can't know the net volume exactly without knowing port volume exactly, but here is what I did:

I was figuring for 2 -3" flared ports 17" in length if I remember correctly... I used a "volume of a cylinder" calc to find out the volume of the ports _Outside_ dimensions to include port wall thickness.

After subtracting port volume, 1 internal brace that goes all the way around, and driver displacement I was left with 2.12 cu ft (internal volume) accounted for wood already too...

I also decided on the 2 3" round ports because JBL rec'd a single 4" port, the 2 3" ports have a touch more cross sectional area...


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## Oscar (Jun 20, 2010)

ScottyGreen said:


> @oscar
> 
> Heres how I arrived at my numbers so far...
> I understand I can't know the net volume exactly without knowing port volume exactly, but here is what I did:
> ...


ok so putting that port volume back into the enclosure, that leaves ~2.3 ft³ airspace. 

So here's the problem. With your *power levels*, there is no kind of port AT ALL that will keep vent velocities down to appropriate levels in that size of enclosure while still remaining *within* the 2.3 ft³. You need to compromise with either lower power levels or enclosure volume IMHO.


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## ScottyGreen (Apr 3, 2012)

hmmm, so I am guessing the the JBL rec'd spec box of 2.25cu ft with a 4" round port would sound crappy??

I figured that having 2 3" round ports with the slightly larger cross-sectional area would be a least a little better than a 4" round port...

a 4" round port is 12.5 inches in cross section and 2 3" are 14" area

I don't want to start an argument, so *please DO NOT* take this the wrong way but why would JBL put out a rec'd ported box size of 2.25cu ft with a 4" port and make it sound bad?


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## ScottyGreen (Apr 3, 2012)

I guess just forget it...

I'm going to go with the data given by JBL and substitute 2 3" round ports (and adjust the length accordingly) instead of the single 4" round and call it a day.

My only question was whether I should tune a little higher for rock music...
I'm going to go with JBL rec'd 30hz tuning in the 2.25cu after displacement.
BTW, their specs are also good for up to 3000w peak, so 1500w rms roughly, without reaching xmax, so I tend to think that JBL knows what they are talking about...
if it gets a little windy in my trunk I'll let you know.

I'll figure it out and post results after listening tests...


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## Oscar (Jun 20, 2010)

the simple answer is that they are likely recommending it based on average power levels and those are simplistic enclosure designs that someone with limited woodworking knowledge can easily create. They are not meant to be "advanced" enclosures by any means what so ever.

So, no that JBL spec'd box wouldn't sound crappy, IF you kept the power levels down to what they would likely tell you. (I seriously doubt they will tell you to really drop the hammer because any and all warranties go out the window). Once you start to get more power into the speaker (which most of us know it can handle), then you need to start deviating from simplistic designs that don't take into account things like port velocities and such.

Two 3" flared ports would indeed be better than a single 4", but at ~1100W RMS, you're looking at core velocities of approximately 51 m/s. That's a lot higher that I'm comfortable with because at very high velocites ports start to "change".


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## Oscar (Jun 20, 2010)

ScottyGreen said:


> I guess just forget it...
> 
> I'm going to go with the data given by JBL and substitute 2 3" round ports (and adjust the length accordingly) instead of the single 4" round and call it a day.
> 
> ...


Oh they know how to build speakers alright, but if you for one second think that ANY of their transducer engineers would run 1500-3000W into a W12GTi with just a _single_ 4" port, well I don't know what to tell ya 

you'll get a couple of free dB's if you tune a bit higher, but i wouldn't tune higher than about 36 hz or so.


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## ScottyGreen (Apr 3, 2012)

Alrighty... thanks for your input...

My spec/enclosure sheet indicates 3000w peak with that design, not sure why they listed it like that, but anywhoo, thanks for your input regardless.

I'll let cha' know... probably going for 30hz tuning in the 2.25 enclosure to keep my velocities a little lower. It will translate into roughly 8 m/s peak velocity difference if I go with the 30hz vs a 32hz tune. 35hz is a crazy amount of port speed with this size enclosure, _double_ the port velocity of the 30hz tune at 60 m/s peak vs 30 m/s peak with the 30hz tune. (that is at 40hz btw)


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## Oscar (Jun 20, 2010)

ScottyGreen said:


> Alrighty... thanks for your input...
> 
> My spec/enclosure sheet indicates 3000w peak with that design, not sure why they listed it like that, but anywhoo, thanks for your input regardless.
> 
> I'll let cha' know... probably going for 30hz tuning in the 2.25 enclosure to keep my velocities a little lower. It will translate into roughly 8 m/s peak velocity difference if I go with the 30hz vs a 32hz tune. 35hz is a crazy amount of port speed with this size enclosure, _double_ the port velocity of the 30hz tune at 60 m/s peak vs 30 m/s peak with the 30hz tune.


I think either you or the program are doing something wrong, no offense. No way port velocity can double with such a small change in tuning.


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## ScottyGreen (Apr 3, 2012)

It was 52.3 vs 30 m/s

nearly double... when my port velocities are really steep, it's not hard to conceive a small tuning difference being nearly double.
They are really steep curves and just a little to the left or right gives you a vast difference in speeds when so steep... if any of that made sense?

Is winisd super inaccurate on port velocities?


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## Oscar (Jun 20, 2010)

it shouldn't be. I've used it before and got good results. What kind of power input are you specifying?


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## ScottyGreen (Apr 3, 2012)

signal input power at 1200 gave me those numbers...

2 3" round ports, 2.25cu, 30hz tuning, says 16.54" length...

I wonder if my driver specs are a little off or something?


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## Oscar (Jun 20, 2010)

If I'm not mistaken, WinISD needs Re to reverse calculate voltage input from the user-specified power input. What Re are you using?

With 1200W I'm getting 60 m/s peak tuned to 30Hz, and 80m/s tuned to 35 Hz.






















BTW, I too have a W12GTi that I need to build a box for, except that it is down for repairs since I have to finish a re-re-cone on it.


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## ScottyGreen (Apr 3, 2012)

Got mine done, sounds amazing!
Tuned it to 32hz and it outperforms my 2 sealed re sex's!

Sounds incredible on rock, i'm converted to ported now.
I thought ported would possibly suck on rock, but it handily whoops upon my re's. Has a good amount of authority from 35-80hz and dances from note to note effortlessly

I'm blown away by this sub and enclosure setup, can't wait to crank it up in the near future, trying to not crank the hell out of it right away till i get a feel for its possible limitations and to let the suspension settle in a bit

GO JBL, you put out a fine sub with this series!


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## minbari (Mar 3, 2011)

If your sex series were sealed, then that doesn't surprise me. Ported can easily get 6DB more output. That is like Having 4x more power

Sent from my phone using digital farts


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## Oscar (Jun 20, 2010)

minbari said:


> If your sex series were sealed, then that doesn't surprise me. Ported can easily get 6DB more output. That is like Having 4x more power
> 
> Sent from my phone using digital farts


It's not like ported gives you +6 dB across the board, its mainly on the low-end. Having 4x the amplifier power would raise the entire response curve up 6 dB, not going ported.

Scottygreen, pics? What porting scenario did you end up using?


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## minbari (Mar 3, 2011)

It gives you 6DB more where you want it. From 25 - 50 hz. You are right, above 50 hz out is about the same

Sent from my phone using digital farts


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## ScottyGreen (Apr 3, 2012)

You guys are correct, after more time to listen and evaluate, it's about the same up top (but slightly more pronounced, _nimble_ I should say) with a TON more low end grunt capability. I find myself dialing down some of the lowest frequencies about 1-3 db at times to make overall sound more smooth and even. I must have a lot of cabin gain or something because I never thought I could have TOO MUCH low end, but I do now if left unchecked in the 31.5hz region of my HU..Overall I'm very happy.
Next week installing my new 18sound 6nd430 and cdt 2" fullrangers.

I used my old home subwoofer enclosure that I built about 3 years ago and just cut the top and back off to get the correct amount of airspace, and cut and reroutered inside ports to correct lengths.

Here is a pic of the home version, the car version looks the same now, just shorter and laid on it's side.

I used a routered baffle over the outside 3" port exits and port "donuts" on the inside to help with any possible chuffing. So far I can only hear slight chuffing when standing at the rear of the car with the trunk open on 30hz and lower, but since I don't really listen to anything with information down that low it hasn't become an issue.

here is that build thread and pics:
Sub Project With JL sub - Home Theater Forum and Systems - HomeTheaterShack.com

pics:


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## minbari (Mar 3, 2011)

Good to here, makes me want to mine all installed. Only difference is I am going with the w15

Sent from my phone using digital farts


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## Oscar (Jun 20, 2010)

the proximity of those ports to the walls drops the tuning somewhat. It's probably tuned lower than you think, I'd bet a $7 bill on it.


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## ScottyGreen (Apr 3, 2012)

The ports walls are only close to the bottom... There is over 6" of space all the way around them at the openings inside and over 8" at the top area over the ports openings. Not sure why being close to the bottom would change anything... even when it was in the home subwoofer version I made sure to have 5" clearance at the top. Maybe the pics are deceiving but there is actually a lot of room around them and even more so now.


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## Oscar (Jun 20, 2010)

anytime the port is close to a boundary like the bottom and/or sidewalls, it makes the port act like it's a bit longer. It's probably not too much though, and no where near how a slot port drops it's tuning.


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## SQLnovice (Jul 22, 2014)

Just got a 12gti. Thanks to everyone that contributed to this thread.


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## teldzc1 (Oct 9, 2009)

So I initially started with Sealed and then switched to a ported 2.3 @ 27hz (ish). I ran that for a round 3 or 4 months. It sounded really good once I got the eq right. You really have to eq it differently than the sealed version. Like ScottyGreen says above, there is waaay too much low end. I had to kill the 30hz range a lot but once dialed in, the low end sounds effortless.

Fast forward to yesterday. Decided to throw my 1.25 cube sealed box back to see what it was like. It sounds ok, if a little underwhelming. 40hz and up sounds great, but I feel like the lowest notes are missing. I did change the eq settings back but I think there's still some more tuning to be had. In the end, I'm thinking ported is the way to go with this sub, but the trade off is that the box is huge and you really need to be able to eq the low low end.


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## jdigital (Dec 31, 2014)

Just picked one of these up. I have a 1ft cu sealed enclosure to throw it in until I build a proper 3.43ft cu ported. Using WinISD I wanted to see the difference between the two

here is the frequency response of the 1cu ft sealed vs 3.43ft cu ported (tuned to 25hz / Qtc 0.707)









and the maximum SPL of the sealed vs ported









the frequency response of the sealed with eq (using frequencies available in the car) vs the ported









I noticed the maximum SPL stays the same after EQ, so if you have the ability to EQ, would that then make the only downside of the sealed vs ported the maximum volume? and if you don't listen to music louder than 100db you wouldn't notice this downside? I don't mind the space savings and faster transient response a sealed enclosure gives.


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## teldzc1 (Oct 9, 2009)

Having had both, I just have to say they sound different. The low end in the ported box just seemed so effortless, but it didn't seem as accurate. Might have been down to my tuning though. Regarding the sealed box, I honestly think the W12GTI needs a little more room to breathe than 1 ft3. 

Sent from my SAMSUNG-SM-N900A using Tapatalk


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## dat_dere_prime (Jul 23, 2014)

So I just picked this sub up along with a jbl pbx 500.1. This 12" will be getting around 800rms at 3 ohms. I heard these subs are actually closer to 4 ohms, is this correct? 

I really love sealed for EDM such as trance and house, so I am thinking about going this route. Should I stick with the JBL recommended box size or go bigger?


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## EricP72 (Mar 23, 2008)

subscribe to this thread as i plan to run either 1 or a pair of the 12" version. hoping to see a box specd for a person who listens to mostly jazz and a little rap. I want accurate bass and SQ is my only concern. I normally used sealed boxes, but i see vented is the way to go. so any help offered would be greatly appreciated.


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## teldzc1 (Oct 9, 2009)

I'd say go for 1.5 cubes sealed first. Honestly it sounds amazing sealed and might be all you need in terms of output.


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## EricP72 (Mar 23, 2008)

ok, i think ima try both, a sealed with 1.5 cubic per sub and a vented @4.5 cuft @32hz.


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## teldzc1 (Oct 9, 2009)

Are you going to run 2 of them? 2 Sealed in a 1.5 cube each should be excellent.


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## eviling (Apr 14, 2010)

omg blast from the past. **** i started this thread. this must be where i got that random rep from haha. I miss that GTI anyone considering this sub, i talked about it, i did it. i ran it ported, 1000 watts rms from an alpine PDX amp at the time 2.2 tuned to 33hrz the port was i think on that box and i beleieve i did easy mode it and bought a pre built on ebay, and yes it was built awesome sounded awesome. if you have the space do it! this is the best sub in the world if you have the space for it! idk about sealed but its still so ****ing big! but i am having such memorible flash backs thinking back because of reading this thread. oh man, this thing would hit like a BEAST. and i had it in my little suzuki esteem awh man. i forget what i did with it..i think my buddy bought it off me for an oldschool car he was resoring.


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## EricP72 (Mar 23, 2008)

teldzc1 said:


> Are you going to run 2 of them? 2 Sealed in a 1.5 cube each should be excellent.


Yes I plan to run 2. I think ima buy a 3 cube sealed and try to find a vented that gives me 4.5 cube vented. Still need to know what to have it tuned to. I wanna try them both. And I drive a 99 durango so I have the room for the pair. Just need to find a box builder or a box already built for sale.


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## mmiller (Mar 7, 2008)

They work awesome in an Ib configuration as well.


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## EricP72 (Mar 23, 2008)

i cant do IB, i have a suv


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## eviling (Apr 14, 2010)

Abythings possible 

Sent from my A0001 using Tapatalk


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