these box calcs seem right?

[OLD_SCHOOL 10+ year member]

how deep is your box internal

 

[wu501 10+ year member]

well the box is 22" front to back on the outside and i used 3/4" mdf so its 20.5" internal front to back.

 

[XTRMEASURES 10+ year member]

displaceemnt is down the middle of the physical port length

true

jamie

 

[wu501 10+ year member]

okay, i looked up some of jmacs posts and im still getting closer to what i said.

Originally Posted by Jmac

Meh, 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

okay the box is 28"w x 22"d x 18"h. this comes out to 5.187 cubes internal before port/sub/bracing displacement.

So i took his formula for port length and here is what i got:

40*1.84*10^8/[5.187*1728*(30/0.159)^2]=23.0658555219959

So where are uo coming up with these longer lengths? Please help me.

 

[OLD_SCHOOL 10+ year member]

if your using 40 in^2 of port area the correct port length is

40*1.84x108/(5.187 * 1728 (30/.159)^2) - (.823 * sqrt of 40 ) =17.86074649 in

you forgot to subtract .823 * sqrt of 40

 

[wu501 10+ year member]

okay i see that. Now how does this relate to port height and width? Im sorry if this is a dumb question. The port is 3" wide x 16.5" tall. so how does that relate to the square inches? You guys had told me like 40 or more inches in the beggining of this post????

 

[OLD_SCHOOL 10+ year member]

if your port is 3 x 16.5 you have 49.5 in^2 port area

 

[wu501 10+ year member]

okay so...

49.5*1.84x108/(5.187 * 1728 (30/.159)^2) - (.823 * sqrt of 49.50 ) =17.2755372569959

so a 17" long port?

 

[OLD_SCHOOL 10+ year member]

check your math

22.753678

 

[wu501 10+ year member]

okay, well im glad thats all cleared up. I originally had 22.65" using winisd. So where did xtrememeasures come up with 42" port length? Well im glad i can finish building my box now the way it was originally planned //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif You guys had me thinking i was so off before. Thanks for the help //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[OLD_SCHOOL 10+ year member]

i just said check dispalcement

 

[wu501 10+ year member]

well thanx bro. I misunderstood you and i apoplogize. Ive been going crazy all week trying to figure out this port stuff and im just glad it makes sense. If you could do me a favor, what is the displacement or at least how do you get it? Or better yet, after port dispacement and sub (.18) and a little bracing will i have around 3.5 cubes or more?

 

[OLD_SCHOOL 10+ year member]

down the middle of the physical port length... there is thread on here expaling step by step how to do it

 

[wu501 10+ year member]

exterior dimensions-28"w x 22"d x 18" h

port wall 1-16.75*16.5

port wall 2-5*16.5

5.15*3.75*16.5 = 318.6 ci

18.5*3.75*16.5 = 1144.6 ci

Total = 1463.2 ci

=.846759 ft^3

sub box= 5.187 internal

- sub displacement (.18)

- port displacement (.846759)

=4.160241 cubes tuned to 30 hz. Still got to subtract a bit for bracing.

 

[wu501 10+ year member]

if i am incorrect on any of this, please fell free to correct me //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif also, i would like to thanks jmac because even though he never got back to me on some questions, i was still able to dig up some of his posts and find some very uselul formulas.