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I was needing help on my system I'm building. It's 2 JL 12w7s and 2 JL 1000/1 amps. I have a 2002 xtreme blazer and I want to port the enclosure tuned to 32 hz (as JL site recomends) but the enclosure measurements are larger than I have available. What would be the problems if I go smaller? Would the port size change? Is it better not to do it at all? Here are their measurements for each sub
sub displacement- .14 ft3
enclosure=(external) 22.75"x15.5"x15.5" with 1" front baffle
port=(internal) 1.75"x14"x24"
All I have is 36"x16"x18"
Any help would be appreciated
thanks

 
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can you post the Thiele-Small parameters of the sub?..I'll let you know what can work in a jiffy

 
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sorry this is what I get from the JL site
fs:27.2hz
qes:0.514
qms:7.807
qts:0.482
vas:2.33 cu.ft.
xmax:1.15 in.
pt: 750 watts continuous
no:0.249%
spl@lw/lm:86.2db
re: 2.47ohm
sd: 84 sq.in.
znow: 3 ohm
hope this helps
thanks

 
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Okie dokie..

Now is that 36" across 16" tall 18" deep?

 
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yes. inside the wheel wells is 36". to the top of the seat is 16". from the seat to the gate is 18".
thanks

 
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External measurements

26" Across x 15 3/4" Deep and 14 1/2" tall..that's with 3/4" MDF walls and a 1" MDF baffle

Here'a a front view. You can mount the sub anywhere centered between the last port insife the box and the outer wall. The port is 2" across x13" tall (internal height of the box)

Front view.. copy and paste it.. Geocities doesn't allow direct linking

http://www.geocities.com/boomhorse/frontview.JPG


Here'a a top view with the top cover off..the lines inside the box are the port walls. they are each 13" tallx11" long for a total port length of 33" There's a 2" space between each part. I'd highly reccomend rounding off the edges to avoid any port noise.

http://www.geocities.com/boomhorse/topview.JPG

The bottom part of the page is the front of your sub box.

I need a better drawing program to fully sesign it for you.


That'll be $5

 
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if you follow the measurements exactly that's a .02% tolerance [IMG]i/expressions/face-icon-small-smile.gif[/IMG]..port tuning is actually 31.3hz[IMG]i/expressions/face-icon-small-tongue.gif[/IMG]

 
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mohawk I'm so sorry. I must not have explained in my first post very well. The measurements they give is only for 1 sub and I will have 2. Now do you see my problem? I thank you very much for all the trouble you went through. You are still the best. I didn't know if you were still busy with the beting season when I originally posted so I also posted on termpro. A guy on there posted could you read that post and tell what you think about what firebirdude said here is the link http://www.termpro.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=40;t=010681
Thanks for your help. Do you have a better suggestion.
Man the problem I have is I'm 30 years old and married. Absolutely NO friends into car audio and no one and I mean no one (shops) in probably 70 miles that knows a third of what you do about this stuff. I live in Alabama and the place is flooded with morons and fleamarkets. Pyramid and rockwood and sony explode from wal-mart RULE!! I have thought about giving up on car audio. This forum was the first one I found and began to learn about real car audio and my first post when you helped me really got me going. I have about 4 forums I go to every day and try to learn at least one thing. Thank god for forums. Dang I need to open a shop!! LOL
I know this is long sorry. Just wanted you to know where I coming from.
Jim

 
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Oh damn I'm good..muahhaha

Okie dokie amigo..

External volume..

16"tall.

15.75" deep

36" across

Here's a pic from the top of the box..

http://www.geocities.com/boomhorse/topnew.JPG

The port walls will be 1/2" MDF..yes 1/2"

the port length will be 11.5" deep..leaving 2.5" and 18" long



Here's a side view of the port..it gets tricky.. the line across the port is a 1/2" MDF pbrace..this has to run all the way through the port because it's only 1/2"... (I worked it out as 2 7"x2.5" ports)


http://www.geocities.com/boomhorse/front2.JPG

Feel free to ask any questions if you need any bit of clarifications..

this gives you 2.75 cubes for the 2 subs after displacement and leaves you with 35 sq.in of port..

Just enough to avoid any noise above 35hz...there will be slight port noise below 35hz though..but very very little music ever goes that low

 
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Here's a graph of your response with my box.

http://www.geocities.com/boomhorse/rspon.bmp

Here's with JL's reccomended box..

http://www.geocities.com/boomhorse/jlrespon.bmp

if you want to add 4" tot he port for 30hz tuning here's what it would look like

http://www.geocities.com/boomhorse/lowtuneres.bmp

Once again..that'll be $5

 
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BTW..this is as big as you can possible go with your measurements and the subs mounting depth.

When you build the box..the top is the last board to go on..it's gonna be tricky to do with the brace inside the port..but I'm sure you'll find a way to manage...

at any shop this box would cost you upwards of $300 due to the complicated nature of it's design and the MDF required and mixed MDF wall thicknesses...

If you use 3/4" MDF for the port your subs will not vent properly...

Now you have the problem about where to mount your amps

 
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ok external dimension is 16" tall 15.75 deep and 36" across. Use 1/2 mdf for the right side port wall (the left side would be outer wall which is 3/4) The port height would be 14 1/2 (box height 16" - 3/4 mdf - 3/4 mdf = 14) First port length would be 11.5" (box depth 15.75 =1" baffle+11.5" 1/2 mdf+2.5" rear port width + 3/4" mdf) Rear port length 18" (is that 18" of 1/2 mdf or 18" from left side wall to end of port?) With 1/2 mdf brace in the center of the port for stability (full length of the port) OK one more thing I know it says 1" baffle but I was going to stack 2 pieces of 3/4 mdf on each other to give 1 1/2" (to save having to buy a sheet of 1"mdf which will be hard to find around here) Now what? What measurement do I change to do that? What about bracing? Do you think I need any? Remember what these subs are and the power each is going to have. BTW this will allow me to fire to the rear which is what I wanted. Thanks for all your help MO. Of all the forums YOU are still the best.
Jim
Edit- I could just glue a sheet of 1/4" mdf to the 3/4 mdf to give me 1" what do you think
do you think I should add 4" and go 30 hz.

 
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All correct..thing is.. you can't use doubled 3/4" MDF for the baffle or the subs might damage themselves from the pressure created between your gate and the gone at extreme output..

As for bracing the box. Just little Triangle braces between the woofers will suffice..

(like a 6"x6" Square cut in half into 2 triangles..)

Sorry my bad.. you can use 2 3/4" sheets for the front baffle...but you'd have to counter sink the subs.. Basically mount the subs on the bottom layer of 3/4" and make the cutout in the top layer bigger to clear the frame of the sub..

Like so

http://www.geocities.com/boomhorse/sub2.JPG wanna buy a 15" Eclipse sub in an extremely well made box BTW? [IMG]i/expressions/face-icon-small-smile.gif[/IMG]

 
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didn't know if you saw my edit
could just glue 1/4 mdf to 3/4 mdf to give 1"
and do you think I should go 4" more on the port to give me 30 hz would it change any other measurements?

 
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you can add tot he port about 6" (29.4hz) without it noticably affecting anything..

Going 3/4" double layered for the baffle would really well..better then 1/4" and 3/4"...

 
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where's my $5 [IMG]i/expressions/face-icon-small-smile.gif[/IMG]

 
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OK all past measurements the same except make back port length 24". Use double 3/4" for the baffle mounting sub to bottom layer and cutting top layer to fit around the sub. Does this sound right?
Thanks for the help.
$5? e-mail me your address

 
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All correct..the port will be 11.5" deep, and 24" along the back wall for a total of 35.5" of port..

I wasn't serious about the $5..but if you want it's dmtp@lycos.com (paypal) it'll get me more raffle tickets for the spline drive lugnuts [IMG]i/expressions/face-icon-small-smile.gif[/IMG]

 
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i have nothing to add but mohawk your a cheap bastard

 
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i could have told you that a long time ago

 
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I just remembered I can't countersink the sub. It has the unique mounting design. Oh well I guess I'll just buy a sheet of 1" mdf (if I can find it).
Later

 
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You can counter sink the subs...but you have to leave about 1/2" clearance around the sub to get the mountong rings back on...


And I am cheap..any shop would have billed the guy $40-50 just for the design..I billed $5 Monopoly dollars