Any mathemititions/gurus....

[R_ADKINS80]

....to help me with this funky equation?

http://www.clubknowledge.com/Car_Audio_FAQ/?t16

I am trying to tune the ports in my Randall 2x12/1x15 cab because it really only has about 6" of port length to begin with which I know probably isn't right. I specifically need help with how to do the parts of the equation with the " ^ " in it. what the hell does that mean and how do i do it?

Thanks in advance.

 

[MrMarkIII]

All I can tell you is the "^" means "raised to the power of", i.e.,
"10^6" means "10 to the sixth power", or, 1,000,000 (one million).

 

[R_ADKINS80]

OK I plugged my numbers into that equation and came up with port vents of 26.147" long. Cab is only 14" deep.....wtf?

 

[MrMarkIII]

Just eyeballin' it, but could you just be off by a factor of 10, IOW, the correct answer is 2.61" ? Or the "cab" is 14 FEET (instead of inches) deep? Just guessing here.

 

[jdurso]

what numbers were you plugging into the equation? did you make sure all your units are the same? I know back in my early physics days, i would always forget to convert everything to the same units. So remember before you do anything make sure all your units make sense and for things like length or volume, make sure you've converted everything to inches.

 

[R_ADKINS80]

Yeah everything was in inches. The freq I plugged in just for sake of keeping it metal was 60Hz because when I was running EQ's I always bumped 60Hz a bit for that heart stopping thump.

 

[jdurso]

So here are the variables and the equation:
LV= [(1.463 x 10^7 x R^2) / (Fb^2 x Vb)] - 1.463xR

Fb - is the desired tuning frequency of your enclosure in Hertz.
Lv - is the length of your port in inches.
R - is the inside radius of your vent tube.
Vb - is the internal volume of your enclosure in cubic inches. To convert cubic feet to cubic inches, multiply by 1728.


Here's what you've provided us

Fb = 60 htz

We're still missing R and Vb to make this work.

 

[R_ADKINS80]

R = 4"
Vb = 11221.875 cubic inches divided in half for 5610.937 cubic inches because it says to use the total volume divided by the number of vent tubes. My cab has 2.

 

[jdurso]

I got 5.738 inches using your values and that equation. just so we're clear though, your port has an 4 inch radius? thats an 8 inch diameter...sounds kind of large.

 

[MrMarkIII]

... I blame the school system... all those taxes wasted... :lol:

 

[R_ADKINS80]

crap...yeah it has 4" tubes.....2" radius.

 

[R_ADKINS80]

Hmmm. Thats crazy. I remember back in my car stereo days when I would want maximum punch in the low end I would use long front ports stopping about a half inch or so away from the back of the speaker box. Made kick drums and palm muted low guitar stuff cave your forhead in.

 

[jdurso]

I got

2.897"

Using a 2" radius (assuming I worked the computers calculator program properly - where's my old TI?!)

me too... well i got 2.891 but i was rounding and didnt feel like breaking out the good ole TI-89