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View Full Version : ARGGGHH!! I cant figure this port Length out!!



flakko
12-05-2004, 06:49 PM
i was calculating port length for a box for a 12" LI,

xternal dimenstions
H: 15.5"
W: 30"
D: 14"

port W= 4"
port H= 13"

with 2.886 cubes and 52" port area, tuned to 25hz.

I did that weird formula for port length and i came up with a really high number around the mid 70's around 77.6"

[52*1.84*10^8/2.886*1728*(25/.159)^2]

Its really wierd, duz that mean i i need lotsa bends in the port like a maze??

any help would be nice!!

IgnoreMe
12-05-2004, 07:03 PM
i was calculating port length for a box for a 12" LI,

xternal dimenstions
H: 15.5"
W: 30"
D: 14"

port W= 4"
port H= 13"

with 2.886 cubes and 52" port area, tuned to 25hz.

I did that weird formula for port length and i came up with a really high number around the mid 70's around 77.6"

[52*1.84*10^8/2.886*1728*(25/.159)^2]

Its really wierd, duz that mean i i need lotsa bends in the port like a maze??

any help would be nice!!

your port length is real long because your tuning is so low. but to answer your question, yes you would need to run them like this. my suggestion though is too tune a little higher for the LI. 30 maybe 32 hz if you still want good sq. hell i went with 37 on my box, and its still nice but im gonna tune lower since i was advised that the sx have a ton of low end im missing out on due to my higher tuning.

repo24
12-05-2004, 07:09 PM
tune higher, use a larger box if you can, use less port area, or use a round port. These should all give you less port length.

flakko
12-05-2004, 07:21 PM
your port length is real long because your tuning is so low. but to answer your question, yes you would need to run them like this. my suggestion though is too tune a little higher for the LI. 30 maybe 32 hz if you still want good sq. hell i went with 37 on my box, and its still nice but im gonna tune lower since i was advised that the sx have a ton of low end im missing out on due to my higher tuning.

wow how long is that port for your box???

is it possible to use 2 slots one on each side of the sub that will split the total port length in half?

repo24
12-05-2004, 07:31 PM
wow how long is that port for your box???

is it possible to use 2 slots one on each side of the sub that will split the total port length in half?
If you use 2 ports on each side of the sub, the length will not necesarrily be split in half. It is explained here (http://www.jlaudio.com/tutorials/ports/index.html#multiples)

flakko
12-05-2004, 08:03 PM
well, i recalculated, with higher tuning (30hz), smaller port area (39"), and larger box (3.4'^3) and i came up with two types of porting. They are only roughy the outline. its not exact. Which would sound the best?

edit-

btw the length is 29"

flakko
12-05-2004, 08:12 PM
You will never need 52 square inches of port area for a 25 Hz tuning ... Unless you have RC's 5' sub ... Or an insane low-end monster of a sub ...

You would probably be fine with 26 square inches, depending on what you're using and how much power you're using ...

well, im going to run it between 420-550w rms

repo24
12-05-2004, 08:17 PM
well, im going to run it between 420-550w rms
you should be fine with an area of 26" then, there shouldn't be much port noise. Make sure you round any edges you have though

flakko
12-05-2004, 08:19 PM
you should be fine with an area of 26" then, there shouldn't be much port noise. Make sure you round any edges you have though

so is should stick with my old volume of 2.8 instead of 3.4??

wat about the port area? still 52" or 39" from my new calculations?

flakko
12-05-2004, 09:41 PM
You can go with less than 26 square inches with a 25 Hz tuning if you're only using that little power :p: ... Especially if you're only using a 12" ...

Although I would tune higher as 25 Hz is REALLY low for in-car ...

yeahh thats true, howbout the 3.4' cubed box tuned to 30hz and about 29 inches of port. that sounds good right??