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View Full Version : How To Tune The Port! Not So Hard



req
10-15-2004, 04:18 PM
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. :nerd:

skeptikal
10-15-2004, 04:22 PM
and the square root of 30 would be 6.

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

Jonahdude
10-15-2004, 04:25 PM
Square root of 30? Try that one again...

req
10-15-2004, 04:30 PM
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
10-15-2004, 06:15 PM
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 :veryexci:

rofl. funny.

Scarenius
10-15-2004, 09:52 PM
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
10-15-2004, 10:02 PM
http://forums.caraudio.com/vb/showthread.php?t=63426

Threshld1
10-15-2004, 10:05 PM
something ive always wondered is how is this forumla derived? anyone have a proof?

LuNaTiC
10-15-2004, 10:57 PM
yes jmac has typed the formula many a time but its still hard to understand for ppl's like me. :spank: :nerd:

DBfan187
10-15-2004, 10:59 PM
http://forums.caraudio.com/vb/showthread.php?t=63426

click click click click click...

jellyfish420
10-16-2004, 02:14 AM
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
10-16-2004, 11:41 AM
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
10-16-2004, 11:56 AM
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
10-16-2004, 02:38 PM
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
10-16-2004, 11:49 PM
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"

jellyfish420
10-17-2004, 12:55 AM
(45 * 1.84x10^8)/(4 * 1728 x (38/.159)^2) enter - (.823 * sqrt 45) your answer will be 15.452"
what is the diff between * and x ? they are both times, right?i did it on my calculator a couple times, and by hand and keep coming up with 204.2" what am i doing wrong???

OLD_SCHOOL
10-17-2004, 01:04 AM
something ive always wondered is how is this forumla derived? anyone have a proof?

http://www.jlaudio.com/tutorials/ports/images/Fb.gif

solve for lv

jellyfish420
10-17-2004, 01:20 AM
ok, now i'm really confused i did the formula above to solve for tuning. first i used 15" and i got like 200Hz. but when i used 204" i got 38Hz. some one, what the hell am i doing?

OLD_SCHOOL
10-17-2004, 01:22 AM
jelly i don't bro, make sure you have all the () in the right places and such

jellyfish420
10-17-2004, 01:34 AM
i typed it in exactly as you did.
(45x1.84x10^8)/(3x1728(38/.159)^2)enter-(.823xsqrt45)

8.28^10/394799572.8=209.727
.823xsqrt45=5.52
209.727-5.52=204.2
what the hell???

Threshld1
10-17-2004, 08:34 PM
http://www.jlaudio.com/tutorials/ports/images/Fb.gif

solve for lv
thats not what im asking, i know what the formula and how to manipulate it, im asking the calculus/physics behind it, where did it come from the same way that ohms law comes from the graph of voltage vs current or E \ I = R or esentialy the slope know what i mean? like why is it .159 times the square of.....

jellyfish420
10-17-2004, 10:38 PM
Using a scientific calculator ...

38/0.159 = 238.9937107
^2 =57117.99375
*4*1728 = 394799572.8
1/X = 2.532930806*10^-9
*45*1.84*10^8 = 20.97266707
- 0.823*Sqrt(45 = 15.45181523

I think you used 10^9 instead of 10^8 ;)

1/X = 2.532930806*10^-9
where did this line come from? please help i really want to learn how to do this on my own. and i did use 10^8, but now that you said that, if i type it in my calculator as posted using 10^7...it comes out right?

BiaBia
10-18-2004, 02:54 AM
10000000, thats how its written out.

req
10-18-2004, 08:52 AM
i am still looking forward to that calculator. ill get my brother to write a program to figure out that arithmatic and see if he cant come up with anything. (he is a CS major rochester institute of tech, and im sure he can program somthing simple like this)

Scarenius
10-18-2004, 11:01 AM
I try, but noone here is willing to answer my questions, so there's no point. The calculators already exist, and mine is just going to be clone of them.

Here's the latest version and it's results. Something is by far off. I need an accurate equasion, and as far as PHP is concerned, none of the ones above here have worked.



Box size: 6192 square inches or 3.5833333333333 cubic feet
Port: 45 inches^2
Frequency: 38 HZ

You port Length!
Calculation 1 : 1724.038737134 inches
Calculation 2 : 69.049928777938 inches
Calculation 3 : -5.5202977266075 inches

req
10-18-2004, 11:12 AM
i understand that, but i do only have limited knowledge of programming, and port calculations. what question was it you needed to awnser?

Scarenius
10-18-2004, 11:21 AM
None really, I just need more ways of doing this equation, because every answer seems different.

My 3 port equaions are as follows, and all of them are off.



$port1 = ($x*(1.84*10^8))/($y*(sqrt($z)*.159^2))-.823*sqrt($x);
$port2 = ((14630000*($y/2)*($y/2))/(($z*$z*($x/144)*1728)-(1463*($y/2))));
$port3 = ($y * 1.84*10^8)/($x * (38/.159)^2); $port3 = $port3 - (.823 * sqrt($y));


$x = the size of the box in cubic inches, $y is the size of the port in square inches, and $y is the frequency.

req
10-18-2004, 11:30 AM
None really, I just need more ways of doing this equation, because every answer seems different.

My 3 port equaions are as follows, and all of them are off.



$port1 = ($x*(1.84*10^8))/($y*(sqrt($z)*.159^2))-.823*sqrt($x);
$port2 = ((14630000*($y/2)*($y/2))/(($z*$z*($x/144)*1728)-(1463*($y/2))));
$port3 = ($y * 1.84*10^8)/($x * (38/.159)^2); $port3 = $port3 - (.823 * sqrt($y));


$x = the size of the box in cubic inches, $y is the size of the port in square inches, and $y is the frequency.

did you try it by hand? maybe the computer is calculating somthing first that needs to go second?

Scarenius
10-18-2004, 11:46 AM
Probably. My math skills are not up to par with this, and haven't been for the past few days.

I'm going to try basically doing it one step at a time, on paper, if it works out, I'll try to punch in the step by step equasion.

req
10-18-2004, 11:57 AM
alright, from what ive heard - thats usually the problem. with peoples math (mine too)

order of operations;

http://www.google.com/search?hl=en&q=order+of+operations&btnG=Google+Search
http://www.mathgoodies.com/lessons/vol7/operations_exponents.html

Parentheses
(Innermost, first)

Exponents
(Powers or roots)

Multiply or Divide
(from LEFT-to-RIGHT)

Add or Subtract
(from LEFT-to-RIGHT)

maybe thatl help

BiaBia
10-18-2004, 02:16 PM
When you do the exponent of 10^8, make sure it comes out like this

10000000

not

100000000

req
10-18-2004, 02:55 PM
yea.
x2

tRiGgEr
10-18-2004, 03:33 PM
My calculator can't go that high...

I have 2.04 cubic feet or 3525.12 cubic inches. 13.5 x 2.75 port and want 32hz tunning. Any one willing to plug it in to there scientific calculator for me? I need the port length.

Man my head hurts.

req
10-18-2004, 03:45 PM
pencil + paper?

i dont have a scientific calculator =P

my brother is working on a working online-calculator, so just hold tight.

jellyfish420
10-18-2004, 03:53 PM
try using the third one but instead of 10^8 use 10^7...i don't know why but thats how i have to type it into my calculator to get it to come out right

req
10-18-2004, 04:00 PM
that may be the trick mr scarman

sanosuke001
10-18-2004, 05:05 PM
I made a port calculator per my brother r3Q's specifications... just ask if you would like anything else added to it...

http://www.cis.rit.edu/~swr9025/sub.php


oh yeah. I saw someone else doing a php-kinda program and I was having the same problem as you were. I figured parens were giving me the trouble so I did something like:

$top = $portArea * 1.84 * pow( 10, 8 );
$bottom = $internalVolumeIN * pow( $frequency/0.159, 2 );
$minus = .823 * sqrt( $portArea );
$portL = ($top/$bottom)-$minus;

and it worked fine that way...

Scarenius
10-18-2004, 05:20 PM
Req: Call me Ravo, it's easier to type.

Sano:
Looks good, you into the whole open source thing?
(would I seriously need a 43 inch port?)
A friend of mine gave me these equations for port size, box volume, and hertz, I'm trying those, too.

Av = (Fb / 0.159) ^ 2 / (1.84 * 10^8) * Vb(Lv + 0.823Av ^ 0.5)
Vb = Av(1.84 * 10 ^ 8 / (Fb / 0.159) ^ 2 / (Lv + 8.23Av ^ 0.5)
Lv = Av(1.84 * 10 ^ 8 / (Fb / 0.159) ^ 2 / Vb - 8.23Av ^ 0.5

sanosuke001
10-18-2004, 05:36 PM
I don't know if you'd need a 43 inch port... I just used the equation that my brother gave me (it was at the top of this article...)

If you have a better equation, let me know and I'll see what I can do.

If you can tell me what Av, Vb, and Lv mean and what those three equations are used for, I'll let you know what they do. (I don't know anything about subs and cars... just programming for my brother req ^_^)

BiaBia
10-18-2004, 05:39 PM
Everyone should have a scientific calculator on their computer.

Start > All programs > Accessories > Calculator

If its not already scientific, do this.

View > Scientific

All done.

sanosuke001
10-18-2004, 05:42 PM
Two things about the one on the computer is that you have to type in every little section of the equation; you can't just type it in one long shot and then find the answer.... the computer one is really only made to do easy stuff...

I guess you could.... but it is very VERY difficult to keep track of parens and stuff.... and I really haven't tried because it was MUCH easier to write a PHP program to do it for me ^_^

req
10-18-2004, 06:39 PM
hey there steve =)

thanks for that! thats a very nice looking calculator. lets see if it works...

WEW - fantastically sweet =D

steve. you are the MAN!

as for that sig, i should punch you in the eye. :evil: just kiddin. i got 2 8's and a 200w amp for $100 steve. whatd ya think ;) eh eh??

thanks for the calculator man. email it to me?

so JMAC- does it work correctly?

**you might as well put a freaking banner on that page steve, cuz people are gonna link like crazy to it =)

Scarenius
10-18-2004, 07:29 PM
More mathematical fun.

http://img68.exs.cx/img68/2828/raveneq.png

a = 0.159
b = 1.84 x 10^8
c = 0.823



ANYWAY, plugging this into the PHP equation gives you this.
$Lv = ($Av*$b)/abs(($Fv^2/$a^2))/($Vb)-$c*sqrt($Av);

# Av = cross section area of port
# Lv = Length of Port
# Vb = Net volume of enclosure
# Fb = Tuning Frequency
$a = 0.159;
$b = 1.84 * 10^8;
$c = 0.823;

I punched in the specs for my planned box. .813 cubes (.753 after sub displacement), a 2X10.5" port at 40hz. It told me -3.7437153658429 inches.

I'm either gettting this right, or not at all.

jellyfish420
10-18-2004, 07:41 PM
look at this i found this...don't know if it will help anyone but here it is.http://www.the12volt.com/installbay/forum_posts.asp?TID=25814&PN=1

req
10-19-2004, 10:25 AM
well i was told by a post form jmac that it was wrong, and it seems to have been fixed. so thats good news.

but we also have this alternate calculator that does feet AND inches. i think thats a large plus!

now all we need to do is put in box thickness, and some genaric volume calculator and throw it to .exe format, and it will be quite a versatile program!!

req
10-19-2004, 10:27 AM
More mathematical fun.

http://img68.exs.cx/img68/2828/raveneq.png

a = 0.159
b = 1.84 x 10^8
c = 0.823



ANYWAY, plugging this into the PHP equation gives you this.
$Lv = ($Av*$b)/abs(($Fv^2/$a^2))/($Vb)-$c*sqrt($Av);

# Av = cross section area of port
# Lv = Length of Port
# Vb = Net volume of enclosure
# Fb = Tuning Frequency
$a = 0.159;
$b = 1.84 * 10^8;
$c = 0.823;

I punched in the specs for my planned box. .813 cubes (.753 after sub displacement), a 2X10.5" port at 40hz. It told me -3.7437153658429 inches.

I'm either gettting this right, or not at all.

no idea what you are doing man. mind explaining what all that is?

sanosuke001
10-19-2004, 12:35 PM
Well, I'm gonna try to make an exe for this **** so you don't have to be on the internet to use it (and my site doesn't have to be up all the time... because network downtime blosw *******)

I'm gonna implement the first equation I had in the PHP page first, and then I'll add more later if we can determine they work correctly. I'll let you all know when the first test is ready.... then someone who knows what subs are supposed to do can make sure it works right ^_^

req
10-19-2004, 02:02 PM
=)

jellyfish420
10-22-2004, 01:45 AM
i think i got it, but will someone check this for me...heres what i got.2.42ft^3 after displacement, 50in^2 port, and 29 Hz.
29/.159=182.3899371
182.3899371^2=33266.08916*2.42*1728=139110801
1/139110801=7.188514428^-9*50*1.84*10^7(i think my calculator is broke ^7 is the only way it comes out where it sounds right.)
66.1343327-.823*sqrt51=
60.31484392in port
thanks also jmac, once i did the 1/x then everything started working.

req
10-22-2004, 01:49 AM
i dunno that sounds good to me.

what sub was it? ill throw those dimensions into winisd...

jellyfish420
10-22-2004, 01:52 AM
ive been using exp, i don't have a x^y button, so i've been doing it right this whole time???
and i'm drawing out a box for 2 RE RE 10's.

jellyfish420
10-22-2004, 01:57 AM
You should hit 1.84 EXP 8 instead, then ;)
either way 1.84exp8 or 1.84 x 10exp7 would work right? so my 60 inch port is right then. yeah, i finally figured this ***** out!!!
hey req thats a nice calc. in your sig. i never saw that before. it gave me the same number that i came up with.

sumone
10-22-2004, 02:16 PM
1/256 - Enclosure designers who just learned how to calculate port displacement

THATS ME

rofl. funny.

you're not alone.... (http://www.caraudio.com/vb/showthread.php?p=546857)

req
10-22-2004, 02:19 PM
=D

im glad this stuff is comming along and im starting to understand this crap...

i gotta reinstall inventor and make some 3d renders of some boxes.

Threshld1
10-22-2004, 05:37 PM
so i take it that no one knows where this forumla actually come from then? i know there has to be a fairly strait-forward physics/calculus proof of this somewhere... its not like some dude was just like hey... this is the formula to tune a port... anyone have any input here?

Scarenius
10-22-2004, 11:27 PM
Don't know, but so far it seems to be working.

OK

10 = 10
10^2 = 100
10^3 = 1000
10^4 = 10000
10^5 = 100000
10^6 = 1000000
10^7 = 10000000
10^8 = 100,000,000

So, let's replace 10^8 with 100,000,000

1.84 * 100,000,000 is static, so let's replace it with 184,000,000

PL = Av * 184,000,000 / Lb * (Fb / .159^2) - .823 * sqrt(Fb)

.159^2 is static, too, let's simplify that.

PL = Av * 184000000 / Lb * (Fb / .025281) - .823 * sqrt(Fb)

The order of operations is
Av * 184000000 (X)
Fb / .025281 (Y)
Lb * Y (Z)
X / Z (A)
.823 * sqrt(Fb) (B)
A - B (C)

C IS THE FINAL PORT LENGTH! Now, to get this all in computer friendly PHP coding.

I tried this out.


Box size: 1301 square inches or 0.75289351851852 cubic feet
Port: 10.5 square inch cross section
Frequency: 40 hertz


You port Length!
2349608838.7372 inches long, 2349608835.4968 after countering effective length


the12volt's calculator tells me 186.00793000000002 inches.

Anyone care to comment? Effective length = length - sqrt(port cross section).

sumone
10-23-2004, 02:33 AM
so i take it that no one knows where this forumla actually come from then? i know there has to be a fairly strait-forward physics/calculus proof of this somewhere... its not like some dude was just like hey... this is the formula to tune a port... anyone have any input here?

basically.

but really, not that I know anything about enclosure design, but a majority of stuff probably depends on the science of acoustics. then you got the theile & small books and stuff. (where do you think t/s params came from?)



[2] L.L. Beranek, Acoustics (McGraw-Hill, New York, 1954).

[4] A.N. Thiele, "Loudspeakers in Vented Boxes, Parts I and II," J.
Audio Eng. Soc., vol. 19, pp. 382-392 (1971 May); pp. 471-483 (1971
June).

[6] R.H. Small, "Closed-Box Loudspeaker Systems," J. Audio Eng. Soc.,
vol. 20, pp. 798-808 (1972 Dec.); vol. 21, pp. 11-18 (1973 Jan./Feb.).


as you can see they're pretty old stuff, but serve as the foundation for today's technology.

also, a while back helotaxi recommended "Loudspeaker Design Cookbook" by Vance Dickason to me.

sumone
10-23-2004, 02:35 AM
I got that stuff from here (http://www.hpcalc.org/hp48/science/physics/spkr32.zip)

Scarenius
10-23-2004, 08:46 AM
Your cars milage is sad. Mine gets between 24 and 28 miles/gallon.

sumone
10-23-2004, 04:53 PM
lol...why'd you have to remind me... yea and acceleration is horrible now. engine speed'll be at like 2000rpm just accelerating smoothly from 0 to 10mph (over the course of 5 seconds).