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View Full Version : I need help with ported box!!! please help



impulsebrklyn
03-20-2003, 11:30 PM
ok im building a ported box for a brahma 10.

I need 1.25 cu ft plus .1 cuft for displacement plus a port 9.5 x 2.5 x 37 inches long that should tune it to 35hz correct. I called adire and thats what they told me

ok now how the hell do i build this thing

11 x 25 x 12 will give me the 1.35 i need but now how do i include the port? can i put it against the wall the around the back? I need help with the dimensions please help. I wanna build this box tonight and tommorow so i can hook it up tommorow when the amp gets here. Chris

I would like to keep the 11 and 12 inch measurments. the 25 is completely adjustable.

can someone draw me a picture? with dimensions?

impulsebrklyn
03-21-2003, 12:59 AM
i need help with the lengths and dimensions of this box. i know it looks like this but what are all the measurments

http://www.clarkson.edu/~calisec/caraudio/box.jpg

Trixter
03-21-2003, 07:49 PM
Originally posted by impulsebrklyn
i need help with the lengths and dimensions of this box. i know it looks like this but what are all the measurments

http://www.clarkson.edu/~calisec/caraudio/box.jpg

Actually the port would have to be 41.75" long to make up for the port end correction factor. If not the sub will see the rest of the wall (from the end of the port to the corner of the box) as part of the port. The correction factor is found by dividing the height of the port in half and adding it to the lenght: 37 x (9.5 / 2) = 41.75. Also remember when measuring the port to measure down the center of it.

impulsebrklyn
03-21-2003, 08:51 PM
what the hell is port end correction factor?

impulsebrklyn
03-21-2003, 08:58 PM
im starting to get pissed here. When i called adire they told me 37 inches long and it didnt mater what direction the port went in. SO if the god **** port is suppose to be 41. 25 inches long my half built box is now garbage

Trixter
03-22-2003, 01:09 PM
Their are right, is is suposed to be a 37" port. But when the port and the box share a common wall, the sub will see the rest of the wall (of the box) after the port as being part of the port. So you add the port correction to compensate. If you were to use a round port or one that does not use a box wall it would be 37".

Here... http://jlaudio.com/tutorials/ports/index.html, they explain it better.

Trixter
03-22-2003, 01:39 PM
If you give me the thickness of mdf your using, I can give you demensions.

So far, 11 x 12 x 25.25 / 1728 = 1.98 - 0.57 (port dis.) = 1.36 - 0.1 (sub dis.) = 1.25

Your going to have to be at least 25.25 long if you want you 12 and 11 to stay. These are internal demensions. Once you add the thickness of you box material it will be longer due to the displacement for the port. As for the port, it will wrap around three sides so you can get the proper length out of it.

ChefJoe
03-22-2003, 07:21 PM
What a load of crap. All the port correction factor is doing is suggesting that the port ends not as a flush end like a tube, but like a 45 degree wedge, with your port length being augmented by half of the port height (shortest dimension). What's really amusing about that is that they're calculating the port length based on the middle of the slot, which is a method which will subtract the same volume as the port correction factor they later add in. They'd be better off telling you to measure the length based on the outside/longest surface of the port.

Trixter
03-23-2003, 01:57 PM
Originally posted by ChefJoe
They'd be better off telling you to measure the length based on the outside/longest surface of the port.

That's what I did. I took his (9.5 / 2) + 37 = 41.75

Trixter
03-23-2003, 02:22 PM
The box will look something like this...

Provided you use 3/4", 'cause you said 11" tall and got 9.5" tall internal...

height - 9.5" (11" external)
width - 10.5" (12" external)
length - 36" (37.5" external)
9.5 x 10.5 x 36 / 1728 = 2.08

port wall displacement
(30.75 x 9.5 x .75) + (8.75 x 9.5 x .75) / 1728 = .16

port displacement
9.5 x 2.5 x 41.75 / 1728 = .57

sub displacement you said is .1 so...
.1 + .16 + .57 = .83 total displacement

2.08 - .83 = 1.25

you or someone else please check these. I'm sure that they are right but I'd feel better if they were checked.