subwoofer enclosure design

it's a long time since i done any of this but i need to make a sub enclosure.
the sub is a JBL GT4-12 and the amp is a JBL 2000

rest of the system is
kenwood kr-v8090 - av amp
jbl control 1's - speakers
jbl gto 508c - crossovers
jbl gto18t - tweeters


at the moment i have this POS FLI 12" sub box with built in amp
and its farting, sounds horrible at higher volumes and makes everything in the livingroom
rattle and vibrate even at quite low volumes and thats not the kind of bass i want.
I want nice tight punchy bass not the low sloppy rattling kind i have now.

having a bit of an argument with a mate about sub enclosures, he's adament i should use a ported design
tuned to about 30hz where as i want to use a sealed enclosure.
I have pdf of the sub which goes into thiele small parameters if anyones interested in seeing it.

so anyone done any of this stuff before and what would be your reccomenation ?

I've got something bookmarked somewhere-I'll see if I can dig it out.

FWIW I bought a cheap but originally quite expensive big car one off my GF's nephew & used that. I'm using the LF out from my AV into an old 60W technics hifi amp. It's behind the sofa & seems good enough to me! Inphase is what's written on it.

There's an awful lot of air moving around on subs. I'm not, initially, quite seeing how you'd get away without some porting.

thanks Ed would be interested in any info you got

good idea running the sub-out into another hifi amp
only reason i'm using the car stuff is it came up cheap enough.

bugger-must have lost the bookmark during a rebuild. It's a bloke who built effectively a big sub attached to a frame rather than an enclosure, so wide open. IIRC the issue he had (then) was properly tuning the amp/crossover to it but he was so impressed with the fullness & immediacy of it that I thought I'd made a note. I was quite taken by it. That should be enough to find it via google which was how I found it. Gets quite techy but lots of useful pics. Def an enthusiast!

If you do find it please pop a link up.

I've used win isd in the past.

LinearTeam

Or bass box pro....or this....

Http://www.mfr-eng.com/toolbox.htm


As long as you can get hold of the thiele small its pretty simple to design your own given tuning and what you want to achieve.


Basically, its a shit sub in a shit box (sorry to be a bit of a git but its pretty awful so dont expect much) designed to be in a car, which in itself is an enclosure. A good bit of thick MDF or birch ply and some glue and screws could make it a lot better. The GTs are a much better sub from a budget view. Much better than those fli crap holes.

I'll be following this thread with interest since my next project is a custom sub for the van. Narrow enough to give really good bass but without taking up too much room.

S.

I had to un plug mine. Far to much bass for this house. Sounds shit now For some reason i cant get the sound up the scart lead so i cant use the tv speakers.

Will pm someone who is a pro at this! And await his info!!

A 10" sealed sub would fit your bill for tight punchy bass

Its a bit of a myth really. You can easily match a basic sealed box with a well designed ported and you get better low extension. The only trade off is higher power handling without unloading the driver.

If its home cinema, I'd go ported.

Originally Posted by E-Man

Will pm someone who is a pro at this! And await his info!!

With that sub there's no point in going more involved than a well sealed 1.25 cuft enclosure. It's not the greatest sub and without proper controls (subsonic filter at least) a ported enclosure will fart about not much better than your FLi...

Spend your time on getting the enclosure good... build it minimum 18mm MDF with a good seal, then paint the inside to ensure a perfect airtight seal... a little bit of fibre-fill won't go amiss but don't pack it out. And don't make it cubed... slope the back edge.

thanks for everyones input so far.

Nigel - yeah i really wanted a 10 or a pair of 8's but this jbl 12 and amp came up at the right price
so going to give them a go and if i'm not happy with the outcome ill sell the sub and box together
and go after smaller drivers.

Okay so here is the pdf for the sub, it gives you reccomended internal volumes for different kind of enclosures
Speedy - you were pretty close on 1.25 ft3
http://www.drop22.com/GT4-12.pdf

For a sealed box it reccomends 28.32l internal volume, i had thought about making just a rectangular box
as i dont have the stuff for cutting the angels, all cuttings going to be done with a jigsaw against a steel edge.
But i did find this on ebay which is a sloped design with close enough internal volume so i could just copy the outer dimensions ?
12 Inch Sub Box 27.5L (ready assembled) 202.403 12" | eBay

i have the mdf already (19mm) got some glue/no nails, 10mm drafter excluder, silicone sealent and 45mm long wood screws comming from amazon
you will also notice on the pdf there is a sugestion for port dimensions for a ported design, i do have a peice of pvc pipe exactly the right size for that.


So thats where i'm at now, still humming and arring weather to use sealed or ported but leaning to the sealed design more
and i'm not sure how i would cut the angles for the sloping back.

All circular saws / Jigsaws have the ability to do angles... just go slow... fill gaps with your NoNails and silicon... (let the silicon go off for a day or so before you drop the sub in, there are theories that the fumes can do bad things to woofer adhesives)

Seriously.. don't bother with the port... unless you need to rattle McD's windows?

or for the purposes of research... do.. but make it blockable and sealable... as you will block it and seal it within 5 mins of running it up...

here's one serious question for you though... AV or HIFI?

Unless you're a Miami Bass enthusiast, you'll not have much need for ported performance for either, but if your system is more AV than Hifi you could go to 1.5cuft... that would enable a little extension for movie booms and bangs... but be careful how you set up the levels on the amp. Too much distortion and your sub will last hours not days...

Originally Posted by Speed3Racer

Seriously.. don't bother with the port... unless you need to rattle McD's windows?
This is exactly what i dont want to do

here's one serious question for you though... AV or HIFI?
Although it's a AV amp I only want a stereo (2.1) setup
It's only source is my computer which i use for everything,
mostly TV and videos but i dont want extended bass for them
and games and music. so i would say HIFI

shit i really screwed the quoting up lol

Personally, I would always go for a ported design, much easier to get sounding right. You can buy the pre-made ports from RS Components or Maplins. Best to buy them because you can choose the diameter and modify the length to tune it (plus it will have the correct flare to avoid huffing). With an unvented design, it's either right or wrong and there's little if anything you can do about it.

Ported designs are more efficient and even if the cone is a bit looser (more extension = more air shifted), you can always turn it down! Assuming you have a separate dedicated amp.