subbox jbl 15inch

[dazleeds]

i need to build a box to hold a jbl gt3_15 sub
pleas help this sub is awsome but i need some box measurements for it to fit in the e30 boot as there isnt much space help help cheers Daz leeds

[chu346]

Do you have the specs of the sub? and how much of the boot do you want to sacrifice?

[dazleeds]

let me know wot specs u need
dnt care bout bootspace want quality sound Daz

[amit325i]

just get in touch with JBL they should be able to give you box parameters.

or try the net, rockford fosgate in my situation did have everthing needed online.

[mrLEE30]

You will need at least a 3 cubic foot internal volume box with a 13inch by 4inch port (i used a piece od plastic drain pipe) all sealed and glued so no air escapes and drill holes in the box and fix sub speaker in with nuts and bolts, not screws. Sounds better facing away from the rear seat and my port fires to the side that you cant see on the pitcure.

Trust me it will sound fantastic.

mrlee

[chu346]

MrLee that sounds about right but what frequency is the port tuned to?

[dazleeds]

mr lee

what size sub is in that box?? and is it a jbl?looks like it if its a 15inch do you still have the diagram and measurements for that box?

cheers Daz leeds

[Jos]

RMS Power Handling: 300W
Peak Power: 2400W
Frequency Response: 29Hz - 3kHz
Sensitivity: 91dB
Impedance: 4 Ohms
Vas: 166.2 liter
Qts: 0.44
Fs: 28Hz
Qes: 0.47
Qms: 6.55
Xmax: 10.01mm
Sealed Enclosure (vol): 50L
Vented Enclosure (vol): 60L

You can use either sealed or ported enclosures but.... as the Qts value is quite high a sealed enclosure would work better with this driver. Also as a 15" driver is physically quite slow the bass response will be sharper and tighter in a sealed box.

Calculated out gives 3.711 cu ft or 105 litres for a Qtc of 0.707 (flat response)

JBL say 50l, using 50l gives a Qtc of 0.915 resulting in a large bump in the response at about 80Hz or so. Thats pretty normal for loudspeaker manufacturers to do, it would be a sound you would be more used to unless you have real hi-fi equipment in your home, if you do then it will sound boomy.

Up to you but I would do a sealed box of about 3 cu ft or so and half pack it with rockwool. Box size would be about 28" wide, 17" high and 12" deep if cube shaped. If you want a different shape I can work it out for you if you give me a rough idea of what you want.

[mrLEE30]

The sub is 12inch and the port frequency is either 40 or 400hz (cant remember) but supposed to be the best resonant frequency. and it does sound better and richer than friends with a similar box.

I just made the box to fit the car boot as i was restricted on height due to convertable roof, so went for sub at an angle as you can see. doesn't really matter as long as the interior box volume is correct.

it was a while ago and i am now tryin to remember if it was a 3 inch or 4 inch port. will confirm.

As for filling with rockwool i didn't bother as the cab boot is so well sealed i went for the best out of car responce (as with a cab you are effectively sat outside the car if the sub is sealed in your boot) there are other designs of ported and un-ported box which not only affect what sort of sound you will acheive, but how hard you can drive your speaker as the air in the box acts as a shock absorber to your basscone. Worth checking on a few websites to design a box best suited to you your amp and your taste in music.

mrlee

mrlee

[Jos]

As for filling with rockwool i didn't bother as the cab boot is so well sealed i went for the best out of car responce (as with a cab you are effectively sat outside the car if the sub is sealed in your boot)

I meant inside the sub box Not the boot of the car

Generally you put some in the box to kill off standing waves and to stop the box from resonating. And your Fb is probably about 40Hz, sounds about right as the F3 cutoff is about 45Hz or so.

[mrLEE30]

Yes i know!!! but filling the boot with rockwoll make cure my license plate vibration!!!!

When i designed the box the speaker came with advice on how to design a box, ported , unported, half ported etc. and the responce graphs showed 2-3dB better out of car resaponce with no sound deadening inside the box (or the boot!!) i figured that i would treat the design as a speaker in a box (the boot) and i was sat outside the box in the passenger compartment and would look for this out of car responce. Fortunately what as actually happened is the bass sounds great inside the car, and feels great in the back seat, but outside the car it is lound and bassy from the front of the car but as you go round the back it is much quieter. This is perfect as i did not want to draw to much attention to the fact that i drive a car with no roof and a load of stereo equipment only a knifeslash away!! i am not sure if this effect is due to my port firing to the side but it certainly works.

and yes it is 40hz which is i am told the best resonant frequency because most musical notes are harminics of this frequency. so there you have it!!

mrlee

[Jos]

Loads of silicone behind the plate then screw it down also cures the vibration problem I have found, then you begin to hear all the other rattles!!

For anyone really interested this site lists all the JBL Thiele-Small numbers including Xmax, which JBL don't list.

http://assistenza.kenwood.it/parametri/jbl-car.htm