How To Tune The Port! Not So Hard

[req 5,000+ posts]

More mathematical fun.

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+ year member]

Well, I'm gonna try to make an exe for this shit 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 5,000+ posts]

=)

 

[jellyfish420 10+ year member]

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 5,000+ posts]

i dunno that sounds good to me.

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

 

[jellyfish420 10+ year member]

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+ year member]

You should hit 1.84 EXP 8 instead, then //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

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 sh!t 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+ year member]

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

rofl. funny.

you're not alone....

 

[req 5,000+ posts]

=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+ year member]

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+ year member]

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 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+ year member]

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+ year member]

I got that stuff from here

 

[Scarenius 10+ year member]

Your cars milage is sad. Mine gets between 24 and 28 miles/gallon.

 

[sumone 10+ year member]

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).