need help figuring this out. im tryin to learn ;)

[IgnoreMe 5,000+ posts]

Originally Posted by JmacMeh, calculators **** ... Use a sheet of paper and a pen, draw out your enclosure, make sure it's right ...

Here's a step-by-step process of how I do it ...

1) Measure your trunk for max dimensions and note TWO dimensions that would be preferable. Subtract twice the thickness of the desired dimensions to get the desired internal dimensions (i.e. 3/4" MDF, 20" height = 18.5")

2) Figure out desired net volume, tuning frequency, and port area.

3) Figure out port length using the following formula :

Lv = Av*1.84*10^8/[Vb*1728*(Fb/0.159)^2] - 0.823*sqrt(Av)

Lv = Port Length in inches

Av = Port Area in square inches

Vb = Net Internal Volume in cubic feet

Fb = Desired Tuning Frequency

4) Draw out a diagram of your enclosure on a sheet of paper and figure out the displacement of the port.

5) Add up all displacements (port, driver, brace)

6) Add displacements to desired net volume and multiply by 1728

7) Divide by the two desired interal dimensions to get the third internal dimension

8) Add twice the thickness of the wood to get the exterior dimensions

im having trouble with step 2. desired net volume: 2.4 ft^3. easy. desired tuning frequency: 29 hz. easy. desired port area? what is that. is that just how big i want the port to be? i thought that depended on the frequency? this is my first time tryin to design a ported enclosure so bare with me.

if i cant figure this thing out i already have ported box plans for a mag but only problem is if i build it with those specs it will be above window line in my explorer so im tryin to adjust it by makin the height smaller while still keeping the same tuning frequency, and same volume.

Click to read more...

 

[italianlifter17 10+ year member]

jmac will help, if u have that hard of a time he can make plans for u for cheap

thanks jmac

 

[italianlifter17 10+ year member]

jmac i got a question too, in those plans u gave me, where do i build the brace

 

[italianlifter17 10+ year member]

the light blue piece on the left diagram???

 

[italianlifter17 10+ year member]

thanks!!!!!!!!!!!!!!!!//content.invisioncic.com/y282845/emoticons/cool.gif.3bcaf8f141236c00f8044d07150e34f7.gif

 

[IgnoreMe 5,000+ posts]

For the 12", 25.5 square inches to 43 square inchesFor the 15", 26.5 square inches to 69 square inches

ok sweet. but now where exactly do these figures come from? are these common figures that people know about or do you figure these things out by math formulas depending on the specs of a woofer? also, what difference would it make to pick 26" (for the 12) as opposed to maybe, 31" ? thanks Jmac. really appreciate it.

 

[IgnoreMe 5,000+ posts]

and having more or less port area is directly correlated to the box size? or could i still have a small box with a huge port area or a big box with a small port area. i would think that everyone would pick the maximum port area then no?

 

[DBfan187 5,000+ posts]

The bigger the port. The bigger the box is gonna be. The port can take up alot of airspace plus you would still need the 2.5cubes for the sub.

 

[IgnoreMe 5,000+ posts]

ok i see. i thought you make the box 2.4 or whatever and the port is part of the box. i didnt know that it counted as its own measurment. well anyways, here is what i have so far done. for port area i went with 30 square inches. so my formula was

Lv= 30*1.84*10^8/ [2.4*1728*(29/0.159)^2]-0.823*sqrt(30) and for port length i got 35.50351466

now i drew out the diagram in step 4 and i need to figure out the displacement of the port. how do i do this? are we talkin about the displacement of the peices of wood that make up the port? i dont see how the port airspace and discplace anything.

 

[IgnoreMe 5,000+ posts]

http://www.caraudio.com/vb/showthread.php?p=546857#post546857

****, i just looked in that thread earlier today after clickin in your sig. dont see how i could have missed it //content.invisioncic.com/y282845/emoticons/frown.gif.a3531fa0534503350665a1e957861287.gif

 

[IgnoreMe 5,000+ posts]

ok well i ****ed up. i wanted my box to be about 2.4 cubic feet. so it was suppose to be

height: 17"

Depth: 13"

Width: 25"

so port length is 35". well i heard the port width shouldnt be smaller than 3" so i figure ill use 10" for the first port wall., that leaves me with 25" left for the second port wall...which would run to the other side of the box. now how the **** do i fix this?

 

[IgnoreMe 5,000+ posts]

i did everythin in external...im guessin i messed up before i even began eh?

 

[IgnoreMe 5,000+ posts]

ok i tried again. box im tryin to make is 2.2 tuned to 29hz. my height is 16" width is 20" and depth is 12" for a total volume of 2.222 cubic feet. anyways the port area i chose was 30 square inches and for the port length i got 39". i did the port displacment calculations and got 1628. is that right? anyone wanna help check it?

 

[IgnoreMe 5,000+ posts]

bump 10 chars

 

[squeak9798 5,000+ posts]

Your port has a displacement of .88cuft using 3/4" MDF ((5.75" x 6.75" [for 30sqin internally + the MDF] x 39") / 1728), if that's what you were asking. Which brings your box volume down to 1.34cuft internally before sub displacement.