Need help calculating rectangular shaped port

[Pantani 10+ year member]

If I have a known circular port length of 2.5" x 11.25", how do I come up with the displacement in cu. ft. of this port so I can figure out the size of the rectangular port I would use?

I have 2 8" Rockford Fosgate HX2's (RFD2208) and am looking to put it in a ported box, tuning around 32ish Hz.

Click to read more...

 

[Buck 5,000+ posts]

idk but he can design one for you: psych0ticnemes1

 

[mrogowski 5,000+ posts]

Pie times Are Squared times Length divided by One Seven Two Eight equals Cubic Footage...

 

[mrogowski 5,000+ posts]

Or in simpler terms:

3.14 x r^2 x L = area in inches

area in inches / 1728 = area in cubic feet

 

[Pantani 10+ year member]

Thank you.

 

[mrogowski 5,000+ posts]

It sure seems like a small port. Something like that I would simply ignore the area and add 10% to the total box volume and call it a day...

 

[Pantani 10+ year member]

That is the recommend diameter and length given by Rockford in their manual for this sub, but only for 1 sub. I was just planning on doubling the volume for the sub, and doubling the volume of the port for my set up.

Using WinISD I came up with a box tuned to 30Hz w/ a single port size (for both woofers) of

Box volume: 1.291 ft^3

Port size: 4.02" x 2' 1 15/16" or .190 ft^3

Doing the math, if I simply double the volume of the recommended port size from Rockford I get a port measurement only about .01ft^3 between what WinISD says vs. Rockford.