Hey guys

I just bought 2x 1000watt 4ohm GT4 JBL subs, with a box built by my friend, the previous owner

The box looks very poor and weak so I want to build my own, but not just any.

I would like to build it to have the best performance possible and for this I would need the best air displacement in the box for the subs

so the question is has anyone built one before that knows how to calculate the best air displacement, how maybe tell me how to do it ;)

it should say how man L in the instruction manual

sorry should mention these are second hand..... all i got was the subs and the shonky box :happy:

might chek on the net try and find how many L, but would still like to know whats the best way to build boxes for subs and all

Program called BassBoxPro.....

Shame it costs $300AUD....

If you can find all the Theile Small Parameters, I can do a bit of work and give you the dimensions you need.

well see i use CAD so i can make the box in 3D and let the software calculate the volum from inside the box, i just more so what to know shapes or techniques that are best for sub boxes i also found these values:

Sealed Enclosure (vol) 28L
Vented Enclosure (vol) 64L

thats for the JBL GT4 12" 1000watt sub

im not quite sure what the difference is between vented and sealed, i know you have vents and so on but why do you need double the volume if you have a vented box?

You need the specs (atleast some) to calculate the EBP.

EBP = Fs / Qes

Gives you a figure out of 100.

50 or less = sealed enclosure

50-90 - either sealed / vented / bandpass

90+ - vented

Ported is a different way of tuning the sub box. Long story which I just cbf explaining during my lunch break.

http://www.klausaudio.com/subwoofer-box-articles/sealed-vs.-ported.php

I prefer Vented, varying reasons. One, I prefer the sound (not the spl). Its harder to destroy a sub in a ported box, its easier to tune if you have the know-how.

Cons - harder to build.

Cubes are no good for sub boxes, I dont like rectangular prisms either. Large flat surfaces can produce unwanted resonant frequencies.

Two subs in one box will give you different dimensions aswell, including in how you wire the subs (push/pull system vs push only).

The thicker the MDF the better (no less than 18mm in your case).

i see

well i dont realy have that much knowledge about all this so im trying to learn as much as possible before i go ahead with the box...

so what values do i need to work it out like whats FS and QES?

http://en.wikipedia.org/wiki/Thiele/Small

Fs - resonant frequency
Qes - total electrical resistance
Qms - total mechanical resistance
Qts - Total 'Q' (based off Qes and Qms)

Read those terms, those are the majority of usefull terms for sub box building.

thanks man beeing alot of help hehe anyway be back on later

ok after doing some calculations i figured i can make a 28L box which will be sealed for each sub and then make a surround for that to fit in my boot....

hows that sound ?

anymore advice and or info?

go ported if you have the boot space
i have a 15 sub in a 3sq foot box and it goes off
but i had the box made by a professional sub box builder
(dorans in sydney)which build my sub box in my old mirage
4th loudest in australia in street a in 2004

please explain what ported means and how much did a pro build set you back?

Make sure 28lt is the net volume, not the gross.


go ported if you have the boot space
i have a 15 sub in a 3sq foot box and it goes off
but i had the box made by a professional sub box builder
(dorans in sydney)which build my sub box in my old mirage
4th loudest in australia in street a in 2004

There's a few 'funny' things about this post :)

yeah ofcourse im not that noob to speakers hehe yeah ill get my dad to help me on CAD and we can get it done to the easy....

cant wait to see them in my boot now all i need is a new amp..

When you're designing.

If you use a 12mm thick floor (as a floor under the parcel shelf, to which your sub boxes would bolt to) you have approx 40cm in height to work with.

Width is about 96cm.

The back of the boot is also slanted (same angle as backseats....more or less)

heres my plan...

i want to replace the whole floor and liner with a new MDF about 10mm thick and new liner then make a door for the spare tyre...

then design a box to fit in the back of the boot and make it match the new floor and all and also might try and preserve the ski flap incase i got something bigger to take in the boot..

do i have to put a piece of MDF under the parcel shelf?

No you dont.

I meant a false floor under the parcel shelf area.....where your subs will be mounted.

ahhh yeah thats what i was planing a whole new false floor and a door for the spare...

to easy ;)

cheers for all your help guys and ill keep in up to date ;)

ported box = round tube inside of box that lets the air out of the box(more of a boom and louder )
sealed = sealed box (tighter bass)
box cost me about the 250 mark (carpeted in grey )
if building your own sub box you car try this site can help
http://www.the12volt.com/caraudio/boxcalcs.asp

ported box = round tube inside of box that lets the air out of the box(more of a boom and louder )
sealed = sealed box (tighter bass)

Other than being wrong, that post is just awesome.

well im just confused about all this sealed, ported, vented enclosures.... i mean guys im not building this set up to win comps and stuff i just want to have my subs not blowing up in my boot so i just want to know the easy and simple way to make it all clean and work fine.

so i planing a 28L box for each sub which will be enclosed.. simple?

Sealed enclosure is just that - sealed. Takes up less room, easier to build and some subs are better suited to these enclosures (based off the EBP).

Vented/Ported - vented and ported are just two of the names for the same type of box. These have a 'port' or a 'vent'. These boxes yes will be on average a bit louder (especially from 25-40Hz range IIRC).

These boxes are bigger, and slightly harder to make. Reason being is, the dimensions have to be spot on. As the vent is used to tune the sub box, being a couple Litres out in calculations could make your sub extremely 'peaky' around the 40-50Hz range.

Sealed boxes are easier to blow subs in. Vented you dont usually go near the mechanical limits of the sub (still possible to destroy the sub through thermal overloading of the voice coil).

Go sealed and enjoy some boot space. :D

Try and make a separate box for each ( or at least a divider in the middle of a single box ). That will mean that if one fails, not much will go wrong.

yeah im going sealed and 28L and seperate box for each sub then making a box for both to make it look clean...

cheers guys

:kb:
Go sealed and enjoy some boot space. :D

Try and make a separate box for each ( or at least a divider in the middle of a single box ). That will mean that if one fails, not much will go wrong.

WTF is boot space? :ninja:

Ill take a pic of the lancers boot and you will see what I mean lol. Can still fit about 7 large and 2 small bodies in it :eeek:

Damn aye - I can fit a packet of chips in mine when its done hahahaha