View Full Version : would someone wanna help me with this one?

bigdub_diesel

02-22-2006, 09:43 PM

i am doing the formula wrong for calculating the length of a port. Maybe i **** at math, but i would appriciate it if someone could plug these numbers in and let me know.

(Av) Port size: (H) 12 inches, (W) 1.25 inches

(Vb) Box Net Volume: 1.75 ft. 3 (21 inches cubed)

(Fb) Tuning Frequency: 32 Hz

I know this is rediculous to ask someone on here to do this for me, but i must be doing something wrong cause im getting like 600 for my port length, and i just wanted to see if there was someone out there that was a whiz at this and could do it real quick or somethin.

Thank you to anyone who looks this over or atttempts the help me figure this out.

I appriciate it.

bimma85

02-22-2006, 09:47 PM

i am doing the formula wrong for calculating the length of a port. Maybe i **** at math, but i would appriciate it if someone could plug these numbers in and let me know.

(Av) Port size: (H) 12 inches, (W) 1.25 inches

(Vb) Box Net Volume: 1.75 ft. 3 (21 inches cubed)

(Fb) Tuning Frequency: 32 Hz

I know this is rediculous to ask someone on here to do this for me, but i must be doing something wrong cause im getting like 600 for my port length, and i just wanted to see if there was someone out there that was a whiz at this and could do it real quick or somethin.

Thank you to anyone who looks this over or atttempts the help me figure this out.

I appriciate it.

I'm not a box calc, so Im not much help :crap: What is the box for? where did 21 in.^3 come from?

bigdub_diesel

02-22-2006, 10:03 PM

not sure, it said on jls site that the net volume needed to be in cubic inches, or at least i thought it did. i know this is stupid, but i figure ill throw it out, and maybe some one can do it

swimfreak26

02-22-2006, 10:23 PM

For a 1.75 cubic foot enclosure I get right around19.35" for the port length. With that size box though, I'd up the port area from 15 sq inches to 25-30ish to avoid port noise and increase output a bit. You would increase the port length to ~40.5" for that size box with a port area of 30 square inches.

EDIT: for the record 1.75 cubic feet is 3024 cubic inches, which is probably where you went wrong.

bigdub_diesel

02-22-2006, 10:45 PM

thanks a lot for doing that. Im actually planning on making 2 sep chambers 1.75 cubic feet each, and putting a port in each one. This is my first ported box, so i wanted to keep it as simple as possible, and not have to zig and zag the port to much, so i figured a one small port for each sub wouldnt be to hard. Im just curious, how did u plug those numbers i gave you into that formula? I was wondering if you could pm me back with that formula with my numbers plugged in so i can do it myself and make sure i get 19 or 20, or whatever it was you figured it to be. then if i need to change my specs i can without posting another thread. I would really appriciate it.

swimfreak26

02-22-2006, 10:53 PM

Port length = ((Av*(1.84*10^8))/(Bv*1728*(F/0.159)^2))-(0.823*SQRT(Av))

Where Av is the cross sectional port area in square inches, Bv is the box volume (net) in cubic feet, and F is the tuning frequency.

In this formula you can use the box size in cubic feet because the conversion is already in place.

EDIT: I've just got this in excel so I ran your numbers through real quick, but you should come up with the same stuff by hand.

bigdub_diesel

02-22-2006, 11:06 PM

thanks a lot, i just ran it and got it.