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dmz2711
12-20-2006, 11:15 AM
I want to build a small wall in a hatchback for either 2 12's or 15's. The problem i have is i am working with a limited amount of space.

I wanted to do the two subs on the bottom and a square port on the top along the roof. I got to thinking what if i went with an external square port, that way i don't have to apply port displacement within the enclosure, giving me a little more room. The question that is buggin the **** out of me, is if i go ahead and do an external port, do i still need to factor in end correction considering that the roof of the vehicle is going to be the top part of the port?

I've read JL audio's site about end correction and they say "remember, the driver can't "see" the length of the port, it can only go by what it "feels" is going on." Seeing that info from the site i think i should factor in end correction even though it is an external port since one piece of the port(the roof) goes on further than the actual port. But, I really have no clue, and need help from some experienced people. thanks

PowerNaudio
12-20-2006, 11:35 AM
since the roof of the vehicle is right on the port and you still have to account for the port opening that is inside the port, yes go ahead and add the end correction to the equation. but even if you dont the difference will be of an inch or two of port length the change in tuning wont be of a great enough deal to make an audible difference.
i hope that helps, maybe some one else can add or take to what i have just explained.

laters

dmz2711
12-20-2006, 11:42 AM
since the roof of the vehicle is right on the port and you still have to account for the port opening that is inside the port, yes go ahead and add the end correction to the equation. but even if you dont the difference will be of an inch or two of port length the change in tuning wont be of a great enough deal to make an audible difference.
i hope that helps, maybe some one else can add or take to what i have just explained.

laters

thanks for the input man, i understand whay you are sayin, and i too think i should factor in end correction by what the jl audio site explains it as. But in my opinion it might make a big difference. If my port would be 20" wide and 5" high, i need to factor in a total of 10" to the port length (half the width of the port). that is why i am trying to make sure i need to do it, or i don't need to do it. **** this is confusing....:crap:

PowerNaudio
12-20-2006, 11:50 AM
can you link me to the tutorial? 10" of end correction seems like way too much to me, but if you link me ill read on it and let you know what i come up with. do you have the subs picked out already? do you have any dimensions for the enclosure picked out? post what you have already set and ill try and help you out more in depth.

dmz2711
12-20-2006, 12:43 PM
can you link me to the tutorial? 10" of end correction seems like way too much to me, but if you link me ill read on it and let you know what i come up with. do you have the subs picked out already? do you have any dimensions for the enclosure picked out? post what you have already set and ill try and help you out more in depth.

no problem, here you go mobile.jlaudio.com/support_pages.php?page_id=165

its all the way on the bottom. for the subs maybe goin 2 15's L7's or somethin similar, dimensions i do not have yet but i know from measuring a while back it is gonna be around 7cuft gross, not encluding sub displacement, and bracing...

saywhat?
12-20-2006, 12:48 PM
end correction is over rated. all that **** goes out the window in a car.

PowerNaudio
12-20-2006, 12:51 PM
what is saying to do is to add half of the hight of the port to the total length of the port, so in your example of 5" of port hight you'll add a total of 2.5" of extra port to your calculations to find out the actual port tuning.

dmz2711
12-20-2006, 01:09 PM
The "h" on their site is actually width. So in my case that would be the 20". Also you are suppose to subtract half the width not add. The "effective length" which is extremely important is going to be half the width of the port longer, therefore the "physical length" of the port needs to be half the width of the port shorter. I thought for the longest time that you were suppose to add, until i read the tutorial a few times. Thanks for the responses. You still think i should factor in end correction?

PowerNaudio
12-20-2006, 06:15 PM
lol, here are two articles that you can read.
http://koti.mbnet.fi/jahonen/Audio/Papers/Portlengths.pdf
http://users.ece.gatech.edu/~mleach/ece4445/downloads/ventedbox.pdf
that should set your mind at ease.

dmz2711
12-20-2006, 07:48 PM
lol, here are two articles that you can read.
http://koti.mbnet.fi/jahonen/Audio/Papers/Portlengths.pdf
http://users.ece.gatech.edu/~mleach/ece4445/downloads/ventedbox.pdf
that should set your mind at ease.


hey man, thanks so much for the help!:veryhapp:

by the way do you have any more links/references, etc. that you can send my way? you can either send me a pm or just post them here. i will take as many as your willing to send. i'm just tryin to learn as much as possible. thanks again