Porting/Shelf port questions

[themarshall]

I'm designing (more like messing around with) an enclosure for a JBL K140 using WinISD. Why K140? Cuz I got K140's. It's based off the fEARFUL 15 sub plan. I think I'm getting there, but I have a few questions about ports that I'm hoping someone can help me with:
1. Is shelf port the proper term for a port running the width of the enclosure?
2. Is the port shelf length calculated from the front of the enclosure or from the baffle, which is recessed?
3. As there is a brace/divider in the middle, is it best considered as 2 ports or 1 large port - subtracting the divider/brace from the port dimension.

I have read an earlier post by greenboy re: dividing WinISD's shelf length by 1.5 and adding the volume behind the shelf to that of the enclosure. I also realize it may be easier to just use round ports, but I'm using this as a learning experience in hopes of putting together a 15/6 (with a 3015LF, not a K140).

Thanks

[billfitzmaurice]

Originally Posted by themarshall

1. Is shelf port the proper term for a port running the width of the enclosure?

Yes

2. Is the port shelf length calculated from the front of the enclosure or from the baffle, which is recessed?

From wherever it vents to the outside air.

3. As there is a brace/divider in the middle, is it best considered as 2 ports or 1 large port - subtracting the divider/brace from the port dimension.

Either way the result is the same

I have read an earlier post by greenboy re: dividing WinISD's shelf length by 1.5 and adding the volume behind the shelf to that of the enclosure.

Not accurate at all. If the duct (port is the opening, duct is the 'pipe' that feeds it) width to height ratio is severe, in excess of 6:1 or so, some adjustments will be required. The same applies if the entrance of the duct is too close to the cabinet back. But there is no simple formula, the only way to be sure of what's going on is to measure the cab impedance to determine Fb (vented box resonant frequency).

[themarshall]

Thankks Bill. I'll keep messing around and see what I come up with.