How To Tune The Port! Not So Hard

[req 5,000+ posts]

other than the JL Audio website formula, here is a modified formula that OLD_SCHOOL gave to me that i wrote in lamens math with a more detailed description so that it was possible to understand without using all the Lv\Av\Fb\Vb terms that arent described very well.

SO;

say the box is 1 cubic foot

the port is 4x12

and its tuned to 36hz

this is where to get the informtion to put into the formula;

the cross section would be (4*12) 48in^2.

the net volume would be (12*12*12) 1728in^3.

and the square root of 36 would be 6.

this IS the formula;

x = cross sectional area of port (inches^2)
y = net volume of box after displacements (inches^3)
z = tuning frequency of port (hz)
PL= Port length (inches)

              x[1.84 * 10^8]             ____
              _______________ - .823 * \/  x 
  PL =        y[z\.159^2]

and remember...

do all math on TOP

do all math on BOTTOM

SUBTRACT .823*square root of X from the quotient of the numerator and denomenator (use dictionary.com if you dont know those words)

the awnser is the port length.

***THANKS TO OLD_SCHOOL FOR HELPING WITH THIS****

this way was eaiser for me. //content.invisioncic.com/y282845/emoticons/nerd.gif.c6fa51ddf7ff75f1c0371fbc648f70ae.gif

Click to read more...

 

[skeptikal Premium Member]

and the square root of 30 would be 6.

even nerds dont mess up like that buddy....

 

[Jonahdude 10+ year member]

Square root of 30? Try that one again...

 

[req 5,000+ posts]

whoops, i was origionaly gonna use 30, but i changed it to 36 cuz its square root was an even# (simpler)

forgot to change that the 0 to a 6... sorry =P

sheesh. wish id of gotten a "woo good job, but change the 30 to 36, you must of missed that"

 

[req 5,000+ posts]

well. prolly about 10 million jmac. but there has been alot of posts lately with all this "how do you tune" and i thought id post this with descriptions and a little eaiser way to read than what ive seen.

is all the info correct? because i know you are a pimp at boxmaking.

//edit

1/256 - Enclosure designers who just learned how to calculate port displacement

THATS ME //content.invisioncic.com/y282845/emoticons/veryexcited.gif.c26a15f316d23068607f36ddacd7a7ab.gif

rofl. funny.

 

[Scarenius 10+ year member]

I hope the formula I did is right...

http://www.epicrevival.net/special/port.php

It does the work for you!

...

This would probably be more reliable.

http://www.the12volt.com/caraudio/boxcalcs.asp

 

[DBfan187 5,000+ posts]

http://forums.caraudio.com/vb/showthread.php?t=63426

 

[Threshld1 10+ year member]

something ive always wondered is how is this forumla derived? anyone have a proof?

 

[LuNaTiC 10+ year member]

yes jmac has typed the formula many a time but its still hard to understand for ppl's like me. //content.invisioncic.com/y282845/emoticons/spank.gif.0d78e34d42ea8780359e903aeb6697d6.gif//content.invisioncic.com/y282845/emoticons/nerd.gif.c6fa51ddf7ff75f1c0371fbc648f70ae.gif

 

[DBfan187 5,000+ posts]

http://forums.caraudio.com/vb/showthread.php?t=63426

click click click click click...

 

[jellyfish420 10+ year member]

sorry but i still cant get it right could you solve the example in the first post step by step. i keep getting like a thousand something inches.

 

[req 5,000+ posts]

I hope the formula I did is right...http://www.epicrevival.net/special/port.php

It does the work for you!

You port will be -5.4009853325908 inches long.

Size of port: 48^2 inches

Net Volume of Box: 2073.6^3 inches

Tuning Frequency: 30 HZ

was a 4x12 port for cross section that is ~5.4 inches long. for anyone with knowledge, does this look accurate? seems kinda short to me.

but good work on the coding for that man, maybe we can get this one to work perfectly!

 

[LuNaTiC 10+ year member]

I hope the formula I did is right...http://www.epicrevival.net/special/port.php

It does the work for you!

...

This would probably be more reliable.

http://www.the12volt.com/caraudio/boxcalcs.asp

Dont give up on that formula, if you get it to work it would be very helpfull for lazy people like me.

 

[Scarenius 10+ year member]

Still working on it. I'm trying out different formulas, not looking for anything better, just looking for consistency.

I'm assuming a negative value means you have to have the port coming OUT of the box. I could be wrong.

Code tinkering today, I wanna allow for w*l*h and MDF thickness instead of having you figure out the cubic inches of your box.

How much (average) would a speaker displace? I'm not going for perfection, just a good DIFY (do it for you) calculator.

 

[OLD_SCHOOL 10+ year member]

hehe i got that formula from some where i don't remember, but jmac has posted it a billion times.... and i owe most my skills to jmac from reading his post and some help he gave me a while back.

for those using a scientific calculator if you enter the the numbers just like this say for a box with 45 in^2 port 4 cubes tuned @ 38 Hz

(45 * 1.84x10^8)/(4 * 1728 x (38/.159)^2) enter - (.823 * sqrt 45) your answer will be 15.452"