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View Full Version : Port formula by hand!? got problems...



ngsm13
10-06-2004, 12:53 AM
Hey, so using the formula @ JL:
http://www.jlaudio.com/tutorials/ports/index.html

I solved for Lv, and got some whacky number (like in the millions). Maybe i'm a retard...but...i need help.

Fb= 32hz
Av=70 (14x5)
Vb=7.25 cubic feet

So, what am i doing wrong, any help would be appreciated! I want to see the exact length i'd need.

Also, the current design i have is:
Av= 70
Vb= 7.25 cunic feet
Lv=18
What's the exact tuning (by hand, i don't trust winisd or ****).

Thanks for any help provided...i'm going to continue to attempt figuring this out. peace

NG

Randy Savage
10-06-2004, 12:54 AM
Convert box volume into cubic inches...;)

ngsm13
10-06-2004, 01:02 AM
Convert box volume into cubic inches...;)

OOOOOHHHHHHH! fer shizzle...so... 7.25 cubic feet would be...

7.25*1728=12528 correct?

peace

NG

Randy Savage
10-06-2004, 01:05 AM
Yup

10chars

ngsm13
10-06-2004, 01:08 AM
PHUCK!!!

It's still ****ed up, i'm a retard....

Any help?!?!

peace

NG

Randy Savage
10-06-2004, 01:16 AM
I got 30.5

supa_c
10-06-2004, 01:16 AM
Ahhh, deletion !
yeah, uncalled for, but so are someother posts ;)

ngsm13
10-07-2004, 11:52 AM
WOW! 30.5 that is extremely off what i designed in WinISD.

Any help on this?


Also, the current design i have is:
Av= 70
Vb= 7.25 cunic feet
Lv=18
What's the exact tuning (by hand, i don't trust winisd or ****).

Thanks for any help provided...i'm going to continue to attempt figuring this out. peace

Thanx, peace

NG

OLD_SCHOOL
10-07-2004, 08:49 PM
I got 30.5

thats is way wrong

av= 70
vb = 7.25
fb= 32

(70 * 1.84 x 10^8) / (7.25 * 1728 (32/.159)^2 ) - (.823 * sqrt 70 ) = 18.49643822

Lv= 18.49643822 by hand

ngsm13
10-08-2004, 11:47 AM
Ok OLDSCHOOL, i realllllly appreciate it! I got flustered....and rushed...and went ahead with an 18" long port. So tuning should only be slightly higher. Thanks you a lot oldschool! peace

NG

OLD_SCHOOL
10-08-2004, 12:55 PM
yeah man your only talking like a 1/2 inch if your using winisd pri with the update it's pretty close

where alot people go wrong is when they try to figure out a second port wall on a L shape length and displacment

ngsm13
10-08-2004, 02:58 PM
yeah man your only talking like a 1/2 inch if your using winisd pri with the update it's pretty close

where alot people go wrong is when they try to figure out a second port wall on a L shape length and displacment

true! that's why i did it this way...i didn't want to do an L-shape port...that is the largest port area i could do and still keep it straight! peace

NG