View Full Version : help with L port

11-06-2011, 05:29 PM
I've been using winisd to design my box and it gave me a port length of 29 in. I'm assuming this length is for a straight port. I know for an L port that the length is measured down the center of the port. Ex: 3 inch wide port. If a box is 16.5 in internal depth, the first length would be 16.5 - 1.5(half the width)=15in. But the actual length of the wood for that first leg would be 13.5 in - right? So the second leg would be 29-16.5=12.5in which would make the wood's length for the second leg 11in?

This image confused me because the wood length of the 2nd leg shows 22" but the port length for the second leg of 24.5" with only a 2.5" wide port. Help me figure this out.

11-06-2011, 06:08 PM
You can just measure down all the way to the back of the port since you'll gain half a port width on the inside opening assuming it runs along the back wall of the box. Really odds are if you miss by an inch or three you'll never notice the difference unles you're tuning for SPL and chasing 10ths in which case you're probably planning to re-tune anyway.

11-06-2011, 06:20 PM
In theory though, wouldn't you just add the width of the port to the total port length when using an L port being that it is measured down the center. The first leg goes half of the width extra and the second leg starts a half width extra equaling the width extra overall?

11-06-2011, 08:28 PM
Well.. Depend how you build the box. Typically you only want to see the baffle up front and the first part of the "L" would be behind the baffle which would be (15" - 1.5 - 0.75) = 12.75". So 29 - 15 = 14". 14 - 1.5 (half port) - 0.75 (port overlap/wood thickness) = 11.75". And if you wanted to get crazy for end correction you would subtract another 1.5 (half port) which would leave you at 10.25" You're going to have a hard time finding 2 calculators that match each other spot on. This is how I calculate it anyway..

11-06-2011, 09:13 PM
I have a kicker sub and they say to add an extra half width to the length when doing an l port as opposed to straight. Have any idea why they say to do that? Also what do you mean by end correction?

11-07-2011, 01:52 AM
JL Audio - Car Audio Systems (http://mobile.jlaudio.com/support_pages.php?page_id=165)

11-07-2011, 10:09 AM
So for end correction the effective length is half the width past the end of the port. So to factor this in the wood length should be half the width shorter than the desired 2nd leg length to factor in this end correction. Right?

11-07-2011, 09:09 PM
Is my thinking here right? I'm stuck at this point in trying to determine my box's dimensions so I can start building. Any help is greatly appreciated.