help finding DIY sub box size

[iwillwalk]

i have a jbl 18' sub speaker & want to build the correct size & shape box

where can i find dimensions ?

here is the info on the speaker

jbl

jbl-1800 GTi model #

J342-103797 serial #

[iwillwalk]

anyone? any ideas where tto get the correct box size

[PrestonTom]

Well,,,,,,, it turns out there is great deal more to it than that.

It is best to start by getting over to the DIYAUDIO forums. First, You will need to find the T/S parameters for the driver. Second, you will need to figure out the alignment (style) you will be using, and this in turn will be dictated by the T/S parameters. It is do-able and ultimately you will find some of the shareware programs to be very useful (modelling the various "what if" possibilities). Unless it is a proven design, don't build it until you have modelled it first.

Good Luck,

-Tom

[Guest " "]

It's designed for a vented enclosure. The Fs number will help size port tuning.

JBL - 1800 GTI

TSP Parameter des Lautsprechers: JBL - 1800 GTI



Hauptdaten:

Qts: 0,43

Fs (Hz): 30

Vas (l): 363



Erweiterte Hauptdaten:

Qms:

Qes:



Sonstige Daten:

Preis: 615

SPL (dB):



Bemerkung:



Elektrische, Mechanische Parameter:

RMS (P):

Re (Ohm): 4

Mms (g):

Cms (vm/N):

BL :

Dd (cm):

Le (mH):

[Guest " "]

step 2.

Thinking something like a KP-480, except with a port instead of a radiator.

so if you plug in 24X24X24 into a sub woofer calculator we get 6.5918 after wall thickness.

tuning a 6.5918 volume cab to 30hz (the Fs frequency) using a 4" tube would require a tube lenth of 2.7824.

if you want to get technical, which I am sure many will, you could place the sub woofer in a plastic bag and put in a tube of water to see how much water it displace's and then adjust the cabinet volume accordingly. The adjustment will either increase the cabinet size by a flea's higher, or change the numbers of the port about as much as a coat of paint will.

now if you wait a few hours...this thread will be pounded on with corrections....it's the fourm way.

enjoy

[michael hurd]

A single 4" port is good for about a 12" driver, and not a very long throw driver at that. With an 18, I would suggest a slot port that has equal to or larger area than a single 8" vent.

[DrWho]

JBL is real good about providing documentation for all their products.

http://www.jbl.com/car/product_support/default.aspx?Language=ENG&Country=US&Region=USA

(the 1800 GTi is near the top in the drop down list)

Here's the enclosure guide for your driver that also contains T/S params:

http://manuals.harman.com/JBL/CAR/Boxes%20and%20Parameters/1800GTI.pdf

Looks like they recommend a little over 11cu ft tuned to 28Hz
(three 4" ports that are 5.5" long). The driver will do 5mm of
excursion, so you'll need to feed it less than 300W to avoid bottoming
it out in the passband. You should also put a 12dB high pass filter
right around 30Hz to offset the cone-excursion below the tuning
frequency to make sure the driver is protected.

However, there
seems to be some inconsistencies in the datasheet. It's claiming an SPL
of 95dB with 2.83V at 1m, but later on the graphs are showing 100dB
with 2.83V for the various cabinet alignements. Also, the posted
impedance plot shows an impedance peak at 70Hz, but the Fs of the
driver is listed at 30Hz. Generally, the max impedance is what
determines the Fs so something isn't right there either.

[michael hurd]

It's a car woofer, and I am sure they are getting the 100 db/ 2.83 v in a car interior.

[iwillwalk]

thanks for the input, but its to much data.....can someone just tell me the sizeof the box & port size

thNKS

I NEED TO GIVE THE DIMINTIONSTO SOMEONE TO BUILD IT

sorry for the CAPS

[DrWho]

Looks like they recommend a little over 11cu ft tuned to 28Hz
(three 4" ports that are 5.5" long).