end correction

[porkchop 304]

i was surfing around another sight and seen a post of a fellar wanting to check his design on a port.

he was told a length by the guy , and drafted the port out accordingly.

the port he presented is the exacrt length he was told.

i was just thrown off by this because it is a slot port, and i thought that the end correction should of been factored in.

i was told it wasn't.

so does the end correction not always factor into a port design?

the port folded so it was so it was not on the exterior wall, but ended inside the box along the adjacent port wall.

thanks for the help.

just wanting to ensure i am equiped with the right info.

chop

edit.... the length given was to be 26.65"

[BKOLFO4 29]

That is 26.83" length without end correction, but end correction is only an additional .875", so I doubt it really makes much of a difference in the port tuning.

edit - maybe that far length is 10 5/8"? I read it as 10 5/6", but I thought right after I posted, 'why would they have a length of 5/6"?'

If it is 10 5/8", then 26.65" is correct w/o end correction, which is only .875". Not going to make much difference unless it is a really small box.

Brian

[andymcdo 3]

What exactly is end correction?

[cobra93 47]

I come up with 28.375" with end correction, 26.625" without.

I don't know the net volume of the box , so I don't know how far off the tuning will be.

I've always understood that you add the width ( or 1 diameter ) to the total measured length for effective port length ( that will cover both ends of the port ). I'm not sure how to figure for flared ends.

[cobra93 47]

End correction > would be the length the air sees.

[rmzsuzuki89 61]

What exactly is end correction?

In a ported enclosure, the active port extents half the width of the port past where the port wall stops in the enclosure.

[andymcdo 3]

So if a port is 4" wide, the port actually sees an extra 4" outside the box and 4" inside the box?

I've got a basic design for a box that is 3.5 cubes net with a 4" wide x 14.5" tall for for 58 in^2 of port area with about 41.3" long for a tuning of 30 Hz.

BTW, I don't mean to thread jack.

[cobra93 47]

It should see 4" total ( 2" per end ).

[andymcdo 3]

It should see 4" total ( 2" per end ).

So should I cut 4" total off the port itself?

[cobra93 47]

Is 41.3" the measured length?

[rmzsuzuki89 61]

So if a port is 4" wide, the port actually sees an extra 4" outside the box and 4" inside the box?

I've got a basic design for a box that is 3.5 cubes net with a 4" wide x 14.5" tall for for 58 in^2 of port area with about 41.3" long for a tuning of 30 Hz.

BTW, I don't mean to thread jack.

It's only half the width, and only inside the box I believe.

[cobra93 47]

I'm pretty sure It's both ends. 1/2 the width x 2 for both ends or 1 width. the narrow ( shorter ) width.

Edited February 3, 2010 by cobra93

[cobra93 47]

1/2 the width if you use the walls of the box as a port wall, according to jl audio. My bad .

If you don't use the walls of the box as a port wall then it's 1 width. RMZsuzuki89 was correct.

Edited February 3, 2010 by cobra93

[cobra93 47]

jlauduio

Look over here.

[andymcdo 3]

Is 41.3" the measured length?

It's 41.3 using a calculator, if that makes any difference. I'll upload a picture later when I get out of class.

Differential Equations 5-7 FTL.

[cobra93 47]

I'd cut 2" of the length, check the link ^^^^.

[andymcdo 3]

I'd cut 2" of the length, check the link ^^^^.

That article cleared up a lot of things for me, thanks.

[porkchop 304]

wow, i walked away too soon, this thread took off!

i use the math and thought process displayed in the jl link.

i just was not sure if i was in the wrong since the port does not truly end along a port wall ( like exterior wall) .

i am pretty comfortable saying that the end correction factor would indeed be applied here.

but once again, i am at a noob level, so i wanted to double check myself.

thanks for all the input though, and the link will definetly help others out.

chop

[Impious 1,476]

Yes, it would need to account for port end correction. But as was mentioned, what's the real audible difference in this scenario? Are you really going to hear a difference if tuning is 1 - 2hz different?

[porkchop 304]

Yes, it would need to account for port end correction. But as was mentioned, what's the real audible difference in this scenario? Are you really going to hear a difference if tuning is 1 - 2hz different?

man i would not think so, i tried that crap with my box...... small steps in freq. don't really seem to be audible with mine.

i was not being anal or picking at the feelar, please understand that...

just have not came across this senario and wanted to ensure i was in the right to assume that it would still apply.

so, yeah i agree, not much differance here, but i was just chaseing the math of it basicly.

thanks

chop

[Impious 1,476]

I wasn't criticizing, just clarifying for others who will end up reading the thread. Many times people learning the more technical side get wrapped up in numbers without considering the actual audible implications.

[andymcdo 3]

So according to JL's article, I actually have to add 2 inches to the physical port length not remove 2 inches. Or do online calculators compensate for this?

I've been using this one.

PORT Size Calculations and Formulas for WOOFER and Subwoofer BOXES

[porkchop 304]

I wasn't criticizing, just clarifying for others who will end up reading the thread. Many times people learning the more technical side get wrapped up in numbers without considering the actual audible implications.

oh, no, i know that bro.....

i agree with the direction you was heading 100%.

thanks

chop

[porkchop 304]

So according to JL's article, I actually have to add 2 inches to the physical port length not remove 2 inches. Or do online calculators compensate for this?

I've been using this one.

PORT Size Calculations and Formulas for WOOFER and Subwoofer BOXES

you will begin to find some do and some don't.

not sure, with out reading if cs's calc. does or not.

it is cool to use the calculators, but the pencil and paper way is sorta cool too.

it looks like you are a wizard at numbers after a few months of boxes build up in your note book.

[bigrank916 72]

Very good stuff here. Im pickin up what yur puttin down. This has led me to figure my own out. Wow...Im off.