Calculating Port Length??

[QuestionMan 0]

Dont think it worked, so go to http://s294.photobucket.com/albums/mm87/MV...=Portlength.jpg. The red line is the right way of calculating port length, right? When i calculate it, i get 18.5" total port length, but when the RE Enclosure calculator does it, it gets 19.625. It can't get the double baffle, so shouldn't the RE calculator come up with 17.75" of port length? I just want to make sure that i'm right or that i'm wrong, 'cause i dont see how it could be that far off.

[creyc 1]

Did you account for the end correction factor? The RE calculator automatically adds it in to final port length.

[QuestionMan 0]

Did you account for the end correction factor? The RE calculator automatically adds it in to final port length.

Nope i didnt, hahah that'd be it. thanks for that. Because everyone says RE is off by a little, i wanted to find out how much so i could add some port length if i had to. <<thats the equation from jls site, and for the net volume Vb, do i use all the volume, or do i take out the port volume?

[shizzzon 461]

i dont know what your net volume or tuning is but u say u got 18.5" of length...

Now, this is correct but you have more acoustical length with this type of port than a standard port.

You may not audibly hear a difference but here is an example of what i am saying-

let's say 18.5" physical length required would tune to 32hz.

Well.. when doing slot ports, divide half of the internal width and add it to the port length.

So 18.5 + 1.875 = 20.375" This is what it will act like and that, for this example, might tune it down to 30hz. Whatever the tuning goal is, if u do not know this, u will actually be tuned a little lower than you think.

[QuestionMan 0]

Thanks, i think i figured it out. Pretty sure i prefer just using the equation instead of using box calculators. But yeah i just added end correction to the port length in the equation and it gave me what the port will actually sound like (34.336 hz). Thanks for the replies, i was just stuck on that for awhile.

[creyc 1]

Yep, I agree with you about doing the calculations by hand!

Every box calculator on the web works a little bit differently and they all have their quirks. You're better off just doing it by hand once than using a calculator and second guessing your work because you don't know if it factors in this or that..etc.

And for net volume (Vb), that's actually after port is subtracted. It's kind of odd in some situations, trying to solve for a number that you need to do the equation, but I get close then plug in my outcome port length and then I get closer.

In actuality Vb should be fixed and decided ahead of time, but often we're more constrained by external volume and let Vb float around a tad.

Edited May 15, 2008 by creyc

[QuestionMan 0]

I'm bringing this back only because i'm not sure of something haha. Please click on the link and look at the picture in the main post, and look at the red line. Is that the correct way to do it, and THEN add the correction factor? or do i just calculate the physcial length of the port (which would be 13.25 if i did that) and then add end correction? don't want to have my box finished and find out its tuned to 40 hz haha.