PDA

View Full Version : Please Help W/ Slot Port Length



Miller
06-01-2003, 08:13 PM
Ok...I'm real confused now with how long to make my slot port. I've tried to figure it out but i'm stumped. My box's external dimensions are 29.5"x15.5"x 16. It is 3.3 cubic feet before displacement. I am going to put 2 12" SE's in it and tune it to 35 Hz. I want to use a slot port that is 14.6" high and 1.75" wide. Please help with how long I need to make it.

ShaunMac
06-01-2003, 08:24 PM
for 35Hz around 12.75" long

Miller
06-01-2003, 08:26 PM
You sure??? I used Win ISD to help with tuning but it says 12.75" long to tune to 35 Hz when it is 3.3 Cubic foot box. However after 2 sub displacements it should be smaller shouldn't it?? Still only 12.75?? Also, you dont count port displacement when you are considering tuning do you?

ShaunMac
06-01-2003, 08:40 PM
Well........ I think I'm sure?
I took off .07cu ft for each sub which gave me 3.16cu ft for volume.

With 3.16cu ft. I got 12.75" long for your port.

You should subtract port displacement. But with such a small port
the displacement is minimal. Thus won't have a big effect on the
tuning freq.

If you have a really long port, you definately should subtract displacement
in order to get the desired tuning freq.

Miller
06-01-2003, 08:44 PM
you see my other thread?? If I go with 2" wide its gonna make a longer port which is going to make me bend it at a 90 degree turn. you know anything about doing that or how I would do that?

ShaunMac
06-01-2003, 08:49 PM
Do you mean like this?

Miller
06-01-2003, 09:05 PM
Yes that is exactly what I mean. How do you attach pictures like that? anyway, that is what I mean. the box internally is 14" deep so if I had it 2 " wide then it would have to bend liek that. Do you know how I would calculate the length if I bent it like that or anything special I have to do?

ShaunMac
06-01-2003, 09:23 PM
There's really nothing special you have to do.

The port just needs to remain 2" wide all the way around.

If the box is 14" deep and you need a 16" long port, that means 2" of the port
must be bent and now travel along the back of the box.

The blue part should be 12.75" That will leave 2" between the back wall
and the corner of the port. The red part should be 1.25" long to give
you a total of 16" for the slot port.

This is just the way I did it. There are many ways to design a slot ported
box.

Miller
06-01-2003, 09:43 PM
you mean the red part should be 3.25" right. You said 1.25", but I think you just did it for 14" instead of 16". Alright thanks alot, that helped.

Red=3.25"
Blue=12.75"
Green=14"

ShaunMac
06-01-2003, 09:53 PM
Actually, the red part should be .75" long. Oppppps!

Miller
06-01-2003, 09:57 PM
.75" long?? If the blue slot port is 12.75" long + the red slot port .75" long then wouldnt that make the port 13.5" long when it should be 16" long?

am I missing out on something here??

Miller
06-01-2003, 10:00 PM
Maybe I understand you. Are you measuring according to how long air would travel down the middle of the port?

ShaunMac
06-01-2003, 10:03 PM
Think of it like this.
The red portion is 14.75" long. If you need 16" total
that means you need 1.25" more(yellow portion).
The wood is .75" thick so you actually need only .75" to get the total
port length.

Miller
06-02-2003, 06:32 PM
ok so I'm settled on making the yellow part of the board piece only .75" long. That will give me 16" length which should tune it to around 35 Hz right? Can you help me a little with the tuning, if the box (before any displacment) is 3.3 cubic feet and I am putting 2 12's and that port in it. Then what will it be tuned to?

ShaunMac
06-02-2003, 07:00 PM
For some reason my computer is acting funny.
I'm having trouble running programs. As soon as
I fix it I'll figure it out.

There are plenty of people that can give you the tuning
freq.

14.6" x 2" x 16" long slot port in a 3.3cu ft box before displacement.

2 12" subs aprox. .07cu ft. each = 3.16cu ft after sub displacement

Miller
06-02-2003, 09:06 PM
alright I'll try to figure that out. The port may be a little thinner the 2" also. Probably somewhere around 1 7/8". Not a big difference, but still a difference. Hoping for no Port noise.