# A Quick Port calculation comparison ?

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#### Scott L

Paid Member
I only have one method of port calculation, so I was wondering, given the specs, if someone out there could run the numbers to see if the answer is the same ?

thanks in advance for any help.

Net Volume Box = 3.0 cubic foot
Desired Port freq. ( Fb ) = 50 Hz
Using 2x 4" i.d. ports

my answer: length of vent = 5.0 inches

#### GM

Except for some early T/S math which calcs a ~6.09" long vent (no flares), all others I have say a 5" length will be 47-48 Hz, so ~4.1" seems the most correct length, but all these assume that the cab's air mass has a ~uniform particle density, so if it's a high aspect ratio cab, then even the shorter one could be too long.

GM

#### richie00boy

I get 4.88 inches so I would say you will be OK at 5 as at least you have some spare to trim if necessary. Tuning seems dangerously high for such a big box, what are you building?

#### Scott L

Paid Member
A Low-mid/ upper bass

I get 4.88 inches so I would say you will be OK at 5 as at least you have some spare to trim if necessary. Tuning seems dangerously high for such a big box, what are you building?