JBL monster build

[BiZKiT]

Ok so im ready for my monster build so input welcome! Ian if you will be so kind as to give me some internal spec for the subs?

-subs: 2 x 12" JBL GT4
http://www.autostyle.co.za/prodview.php?prod_id=4612&pid=sound&cid=subs&pg=2&showall=&brandstr=&str=

-port will use same as in old build!


-wood to use is 32mm mdf

and want to try keep it 450mm x 450mm so its fits in the space i have, to make up for size i will be going up so lets see what Ian gives me for internals but guessing 1000mm to 1500mm high...

This will be my Dec project 

[JimGore]

"Monster Build" may be a bit of a strong choice of words for this project, but I am happy to go with you on this one 

I need those drivers to measure T/S parameters my man.  You know the drill...

Ian.

[Timber_MG]

I had a look at this woofer a while back and from parameters I found it likes a large box (think 300l for the pair) tuned 20Hz or a bit higher. Perhaps use more bracing (pine ply works nicely) in stead of 32mm walls to save on internal volume.

I'd recommend not splitting the chamber and building a large vent using a slot or a large diameter port (like 150mm upwards). The bigger your box, the shorter your port for the same tuning.

[chris]

Mine, tuned to about 30Hz was +- 130l. For a single vented box.

[BiZKiT]

"Monster Build" may be a bit of a strong choice of words for this project, but I am happy to go with you on this one 

I need those drivers to measure T/S parameters my man.  You know the drill...

Ian.

is there no other way bud, i just cant find a gap this time of year

[JimGore]

You can't find a gap to drive over to Woodmead?  It will only take 10 minutes or so to do the measuring my man..

I can definitely do the paperwork using the JBL published specs, but if you are planning a serious build, then it's worth while having the actual parameters measured from the drivers themselves.

Ian.

[BiZKiT]

You always make such a convincing argument bud maybe tomorrow early? Ill pm you...

[Timber_MG]

Response to PM in the thread:

Just get Ian to measure them. He has a very neat Woofer Tester for that purpose that'l give you T/S parameters very quickly. My sims pointed to very large vented enclosures or ~80l sealed and stuffed with a lot of power and some EQ. I don't have the parameters I modeled with at hand.

32MM MDF gets to be bastard heavy. I like using Oak for cross and pine ply for shelf bracing. It's easy to place cross braces if you have shelves on the inside of your panels and it is really not that much more work. I have built MDF subs for 18s (60cm x 60 cm x 70cm) that were so stiff, nobody believed me when I told them that they were 18mm MDF (45 degree bracing inside with crosses and shelves). Cabinetry really does make all the difference when talking quality subwoofers.

Placing shelves on the interior panels allows you to easily cross-connect them properly with simple glue-up technique (chased with a fastener if you want to make really sure). To save weight and material you can taper the shelf depth down towards the edges of the cab. Easily done with even a handsaw with pine ply. Pine has a Modulus of Elasticity of around 9-10 (oak ~13) with MDF at around 2-3 so for structural bracing the material choice helps with stiffness (and pine ply is nice and cheap and for cross braces oak can be had cut up by your local lumberyard if you go down that route)

[JimGore]

Ian if you will be so kind as to give me some internal spec for the subs?

Perhaps this is a golden opportunity for you to start learning how to use WinISD. 
Download from here: http://www.linearteam.dk/default.aspx?pageid=winisd

Ian.

[undefined.za]

Why not try a sealed build this time Bizkit?

[BiZKiT]

Perhaps this is a golden opportunity for you to start learning how to use WinISD. 
Download from here: http://www.linearteam.dk/default.aspx?pageid=winisd

Ian.

    

do i look like the pc type...

[BiZKiT]

Why not try a sealed build this time Bizkit?

last time did not like sealed to much....

[BiZKiT]

ok how does this winISD work

[JimGore]

ok how does this winISD work

You don't honestly expect someone here to write you a manual on how to use WinISD do you?  You can download some documentation, etc and read it up.  If you are not the PC type, then perhaps this is a double opportunity - also learn how to use a PC 

Ian.

[Timber_MG]

Is this thread headed for the open board? Headed a bit far off the diy heading.

run the app. You'll figure it out in short order and see the trade_offs of a 70 l sealed versus a 150 l vented.