# Default Ideal Enclosure for the JBL W12 GTi MKii?



## frankmehta (Jan 20, 2009)

A fibre glass enclosure for my W12 GTi is not giving me good enough results in my boot, and I am now running off a makeshift enclosure that measures roughly around .7 cu ft. 
I am making a new MDF enclosure for the sub.
NOW, the JBL sub documentation says that the enclosure must be 1 cu ft. in size. 
They haven't given the exact dimensions, and I am stumped as to how to go ahead. I am enclosing the PDF. Please advise me as to how to go ahead with this. According to their specs, the enclosure turns out to be a cube of 12.5 inches each. Which leaves very little space behind the sub when mounted. Please help!


----------



## sqnut (Dec 24, 2009)

looks like you will get the flattest response in a sealed box. Most manufacturers though quote a slightly smaller box than ideal. Qt is also suited for a sealed box.


----------



## frankmehta (Jan 20, 2009)

so what do you reckon? 1 cu ft will just not cut it right? what should be ideal? ANDY, you around?


----------



## 14642 (May 19, 2008)

Well...unless you're building the box out of 1/4" MDF, 12.5"^3 isn't a cubic foot. All JBL woofers are designed so that the motor is the controlling factor and the woofer depends far less on the box than a woofer with a higher Qes and lower Qms (think old Solobaric for the opposite of JBL woofers). 

In all cases, I prefer vented boxes to sealed boxes, but you may not have enough space for that. The 1 cubic foot box works fine. How much power will you use?


----------



## frankmehta (Jan 20, 2009)

I have a clarion dpx11551 entirely dedicated to the sub. that makes it about 1100 odd watts of RMS power. space is not at a premium and I am willing to.make a large enclosure. trouble is, I have no one to actually make a nice vented end enclosure hence have to go the sealed way.


----------



## 14642 (May 19, 2008)

Wow. no one in India to make an emclosure? Where in India are you? I'll find you someone who can do this work...


----------



## DanMan (Jul 18, 2008)

Andy Wehmeyer said:


> Wow. no one in India to make an emclosure? Where in India are you? I'll find you someone who can do this work...



WOW. THAT'S a GLOBAL product line manager, for sure. And then some.


----------



## teldzc1 (Oct 9, 2009)

I'm interested in the same answer for sealed. I have it tentatively in a 1.25 sealed and stuffed and it sounds good so far, but I'm wondering if marginally more space (1.5-1.7) will net any improved results w 750 watts.


----------



## 14642 (May 19, 2008)

No, that's the point about the motor--box building should be simpler and less critical. Marginally more space won't make a big difference.


----------



## teldzc1 (Oct 9, 2009)

Thanks Andy, I won't stress too much about the difference then. Will more power net better results? Been considering a jump to 1k watts.


----------



## mikey7182 (Jan 16, 2008)

teldzc1 said:


> Thanks Andy, I won't stress too much about the difference then. Will more power net better results? Been considering a jump to 1k watts.


More cone area or moving from a sealed to vented enclosure (my preference as well) will make more difference than 250w. Get a second sub and feed them 500w a piece or put the one you have in 2-2.5 cubes vented, tuned in the high 20s/low 30s.


----------



## invinsible (May 4, 2009)

Andy Wehmeyer said:


> Wow. no one in India to make an emclosure? Where in India are you? I'll find you someone who can do this work...


Andy, there are some atleast I know of building enclosures since more than 2 decades who could build good ported / sealed enclosure here in Mumbai. However, I suppose Frank isn't sure who's the right one. 
I had modeled the freq. response and looks like 1.4cu.ft could deliver good smooth response. But, in most cases the smooth response is something that doesn't match to everyone's taste. Someone look for added kick, chest hitting bass will be more happy with the ported enclosure as you suggested.

[email protected] You could get well ported box either in round port or even the slot port for that matter. It's just that you need to decide on preference, sealed or Ported


----------



## frankmehta (Jan 20, 2009)

As of now, I am not keen on going ported. Reasons for this are:
1. Absence of someone who actually KNOWS what he is doing, when he is designing a vented enclosure.
2. I don't want it to sound too loud, which I know, will surely do, if I go vented, since we don't really know anyone who can fabricate the enclosure to the exact specifications.

Andy, if I am doing a sealed enclosure with 0.75 " MDF, then what should I keep the dimensions as?? Space is not an issue again, and the specs mentioned in the manual state 1 cu ft. But I have a hunch it will play better in a larger enclosure. Please highlight the exact dimensions, so I can be off and have the damn enclosure made, and enjoy the sub that everyone else on this forum (except for me) is raving about :-(


----------



## cam2Xrunner (Apr 30, 2005)

Have you considered mounting the sub IB?


----------



## frankmehta (Jan 20, 2009)

I did give it a thought. But the manual CLEARLY mentions that this sub is not recommended to be mounted in Infinite Baffle. Besides, with the amount of power I am giving it, I might risk suspension damage in IB.
Also, I might have to alter my entire boot to go IB, since my amps are mounted on the rear baffle. Lots of complications. I would have preferred and practised IB if the manual hadn't said so.
THIS is the first sub that has been behaving iffy in my car since day one. Very fussy about the enclosure I place it in. Paradox to what Andy is saying. maybe it's the cabin acoustics in my car, but that is my bad luck. Need to address this soon.


----------



## cam2Xrunner (Apr 30, 2005)

IB with this sub is very popular. Do a search on this subject, tons of threads. Here's a good one.

http://www.diymobileaudio.com/forum...i-ib-heard-one.html?highlight=w15gti+handling

I'm doing a w15gti IB in my IS300 through the ski hole pass through.



Andy Wehmeyer said:


> They work great in IB and will play louder at low frequencies (below 50Hz) in IB than in a sealed box.


----------



## frankmehta (Jan 20, 2009)

Then why the contradiction in the manual?? I am surprised!



> While infinitebaffle
> mounting of GTi Series subs is
> possible, power handling will be
> compromised since there will be no
> ...


----------



## sqnut (Dec 24, 2009)

Frank,

Get a sealed enclosure made at 1-1.1 cuft. Install the sub and run it for a couple of days. Then add some fibre glass wool to the cabinet. This has the same effect as increasing the box size by 10-15%. Run it again for a couple of days and see which option you like better. It really isnt that difficult. I just hate ported boxes period. Have yet to hear one that did'nt sound boomy.


----------



## frankmehta (Jan 20, 2009)

Thank you but have done the exact same thing you mentioned. Maybe a bigger box would help. Waiting for official word on the man who's actually heard a lot of this subwoofer ;-)


----------



## invinsible (May 4, 2009)

Here's the size you could consider i.e. Outer dimension = 15 "height x 15"width x 15" depth.
This would give internal volume of 1.37 cu.ft with depth includes 1.25" front baffle.


----------



## t3sn4f2 (Jan 3, 2007)

Using a sealed box when a low tuned ported box is an option is like driving around with your parking brake on. Go with a ported box, EQ it to sound however you like and enjoy the extra output and/or power savings.


----------



## sqnut (Dec 24, 2009)

frankmehta said:


> Thank you but have done the exact same thing you mentioned. Maybe a bigger box would help. Waiting for official word on the man who's actually heard a lot of this subwoofer ;-)


According to what Andy has said, you wont hear much of a difference between a 1 and a 1.2 cuft enclosure. Try it both ways and see which way you like it better. If you still don't have it the way you want......some subs are designed to play best in a ported enclosure. If this is one of those...... 

How do you want the sub to sound? Whats wrong with the sound in your current 0.7cuft enclosure?


----------



## frankmehta (Jan 20, 2009)

The present problem with my sub is that the bass sounds out of sorts. Low frequencies are killed, higher frequencies of bass accentuated and the entire 'flatness' that one should experience is absent. There is an inadvertent absence of that 'thump' which one associates with subbass. I can get it to play in phase with the fronts and rears, and the imaging is also correct at times. But otherwise it's not at all hunky dory.
Tried RTA but that was absolutely fruitless. 
In all, the sub isn't playing with the authority it should play with, considering that I am giving it almost 1200 W of RMS power!


----------



## sqnut (Dec 24, 2009)

Power is certainly not an issue . Nice sub amp. If you're looking for a bump around say 30-40hz, you would need a ported box. A sealed box will not give you this bump. If you feel the lower end is missing and the upper end of the sub is loud and boomy it could be combination of small box and a high lpf on the sub. Where do you have it cut off? Try crossing the mids and sub around 50-63hz. This will also help a lot with imaging the sub bass upfront.

I have my 12" in a sealed 1.1cuft box off like 400 watts. I like the notes to flow seamlessly between the sub and mid bass. So while I don't have chest thumping bass (lower power) the notes flow effortlessly between the sub and mids and the sound stage has great solidity. I have my sub mid xover set at 50hz and even the lowest of low notes are top of the das and upfront.

Again, I have not heard the JBL sub and if Andy says that the sub was designed for a ported enclosure.....there is a company in Bangalore that makes these boxes. You can give your specifications and they will make the boxes. Both with slotted and tube ports.


----------



## t3sn4f2 (Jan 3, 2007)

Read this!


----------



## 14642 (May 19, 2008)

Frank,
Have someone build the ported box that's on the enclosure sheet that comes with the woofer. It'll be exactly what you want. BTW, the woofers work great in IB.


----------



## frankmehta (Jan 20, 2009)

Andy Wehmeyer said:


> Frank,
> Have someone build the ported box that's on the enclosure sheet that comes with the woofer. It'll be exactly what you want. BTW, the woofers work great in IB.


I am now contemplating IB. Trouble is, again, if I am giving 1200 W to the sub in IB, will I risk damaging the suspension?? Since there is a LARGE volume of air involved in the equation in IB.



sqnut said:


> Power is certainly not an issue . Nice sub amp. If you're looking for a bump around say 30-40hz, you would need a ported box. A sealed box will not give you this bump. If you feel the lower end is missing and the upper end of the sub is loud and boomy it could be combination of small box and a high lpf on the sub. Where do you have it cut off? Try crossing the mids and sub around 50-63hz. This will also help a lot with imaging the sub bass upfront.
> 
> I have my 12" in a sealed 1.1cuft box off like 400 watts. I like the notes to flow seamlessly between the sub and mid bass. So while I don't have chest thumping bass (lower power) the notes flow effortlessly between the sub and mids and the sound stage has great solidity. I have my sub mid xover set at 50hz and even the lowest of low notes are top of the das and upfront.
> 
> Again, I have not heard the JBL sub and if Andy says that the sub was designed for a ported enclosure.....there is a company in Bangalore that makes these boxes. You can give your specifications and they will make the boxes. Both with slotted and tube ports.


Thanks for that absolutely honest and reassuring advice. IS it possible to PM me the name of that place that makes boxes in Bangalore? I will contact them tomorrow and ask if they can build it and ship it to me.
Cheers mate!


----------



## frankmehta (Jan 20, 2009)

t3sn4f2 said:


> Read this!




that link was some FANTASTIC reading mate! Very very good stuff. Thank you :laugh:


----------



## frankmehta (Jan 20, 2009)

1. I have been running this sub ported since a year in a 2.5 ish cu ft enclosure. It's sounding quite good, but I think the port is slightly wrong in design. The length of the port is wrong. Does ANYONE know where I can get a made to order port (or a readymade one) FOR the W12GTi???

2. THIS is one question I wanted to ask since a long time. I know people here have done the W12GTi in IB form since donkey's years, but WHY does JBL stress in the manual that this sub is NOT meant for IB???? I am quite intrigued by the way they have put it in the user manual. 
Why I ask this question is, CAN I DO IB? I am giving about 1200 W RMS to this sub. Is it going to be TOO much for the sub in IB form???


----------



## invinsible (May 4, 2009)

You could order the port from here https://www.madisound.com/store/index.php?cPath=404_85

Get a 4" PORT complete kit and than cut the length as per tuning freq. requirement.

You could do IB however you will have to limit with the power and use subsonic filter in order to control the excursion at the lower frequency that could damage the sub.


----------



## HCCA (Apr 6, 2007)

I am running a pair of these in my vehicle. 1200W/ each, sealed! They are in 1cft enclosure/ea. With EQ, they sound very good. But, to address your multiple questions....the ported enclosure can work. But, it will require a larger enclosure. The sealed enclosure will work. But, while the factory manual specifies 1cft, I think 1.7 cft would work best (based off of Win ISD data). * 
I tend to prefer the sound of larger sealed enclosures. * Though, Andy is right, it won't make a very large difference in output.

Mounting them IB will also work, but you will not need the 1200 Watts, you are feeding them. Something much less will work better. Say...200-250W. 

At the end of the day, if you are running just a single 12"....I would run it ported. You can turn down your gains, and 1200 w should be ok.


----------

