I Need A Maths Whiz's Help

[weasel]

ok i need help figuring out this equation


Where Av is the cross-sectional area of the port (in square inches),
Lv is the length of the port (in inches)
Fb is the tuned frequency of the port (in hertz)
and Vb is the enlcosure's net volume (in cubic inches).

It's to figure out the length of my ports for my new Sub box

the figures are

Av = 4 or 9 (haven't decided yet)
Lv = This is what i want to know
Vb = 16.5
Fb = 53

Unfortunately i was too busy dickin around at school to pay attention, everyone can remember the whole "how are we gonna need to know this when we leave school" arguments you had with your teacher   well yeah now i actually do need it  

if you want more info go here http://www.jlaudio.com/tutorials/ports/index.html

there will be free Karma for whoever can get this

cheers >weasel<

[weasel]

err thats a bit hard to see sorry the JL site has a white background so i thought it woulda came along with it but if you highlight it you can see it easier

Cheers >Weasel<

[bungs]

Somebody check me because i'm not too good with this myself, but i worked it out to be:

Lv = .159 (Av (1.84x10^8)) - Vb(.823 sqrt(Av)) all divided by (Fb^2)x(Vb)

 

[aussie-gli]

Here, I've put it all in a excel spreadsheet for ya...

Just fill in the gaps...

Download here!!

[Mr Trx]

my answer was... when u use 4 the answer is 399.81   and when u use 9 the answer is 900.804 hope it's right  

[Mr Trx]

wow mines wrong lol but y dont u buy a sub box from jaycar??
 and how many inch is ur sub?

[weasel]

Posted by: aussie-gli  Posted on: Yesterday at 10:42:22pm  
Here, I've put it all in a excel spreadsheet for ya...

Just fill in the gaps...

Download here!!

ok i used the spread sheet you made up and it's giving me answers like if i want to tune it to anywher near 53 on like a 4² inch port it needs to be like 400 inches long WTF

Posted by: Mr Trx  Posted on: Today at 03:26:29pm  
wow mines wrong lol but y dont u buy a sub box from jaycar??
and how many inch is ur sub?

i don't think your answers were out at all not after using aussie's spread sheet
I don't want to buy another generic box cause i want one to sit in my boot nicely and be custom made for my boot
and i'm running two 12" subs

[weasel]

i've just figured it out i was going over everything and i realised it says to use the area of your port in SQUARE INCHES and volume of your box in CUBIC INCHES so with new figures

Av= 4²
Vb= 16.5³

and it all works out a crapload better and more believable

thank you all very much as i promised you shall all recieve karma from me

cheers >weasel<

[Mr Trx]

damn that spreadsheet smakes life al;ot more easier... lolz i did mine on pen and paper and a lot of thinking (witha help of a calculator. anyway hope it turns out well weasel

[Tim-E]

oi is the answer Lv = 2.606322 where Av = 4 squared = 16

fuck excel, good ol' pen and paper, lots more fun! hehe

[Tim-E]

wtf, i just looked at that excel spreadsheet now, and by trial and error (adjusting the Lv values until Fb equaled 53) it reckons Lv is -0.09323.

but then when i put that back into the equation it doesnt work out?

For now i am trusting my pen and paper method  

[aussie-gli]

Fb is the tuning frequency. If you want to to work out Lv,  you need to rearrange the formula to make Lv the subject.

Punch this into that same spreadsheet.

=(((B3*(1.84*10^8))/((B6/0.159)^2))/B5)-(0.823*SQRT(B3))

[aussie-gli]

AND change the other formula to

=0.159*SQRT((B3*(1.84*10^8))/(B5*(B4+0.823*SQRT(B3))))

[Tim-E]

yeh i did re-arrange the equation:

Lv = Av(1.84x10^8)     - (0.823x4)
       (Fbx0.159)^2xVb


and it gets Lv = 2.606,

is this right?

[weasel]

Posted by: Tim-E  Posted on: Aug 28, 2003, 04:22PM  
yeh i did re-arrange the equation:

Lv = Av(1.84x10^8)    - (0.823x4)
      (Fbx0.159)^2xVb


and it gets Lv = 2.606,

is this right?  

Well thats what i got too so i'm assuming thats right

and also does anyone think 53Hz is too high Beefy's got me thinking and i just wanna Know if i should go lower say aroud 45Hz  


cheers >weasel<