caculating ports

Printed From: the12volt.com
Forum Name: General Discussion
Forum Discription: General Mobile Electronics Questions and Answers
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=110221
Printed Date: May 13, 2025 at 8:55 AM

Topic: caculating ports

Posted By: reyoung759
Subject: caculating ports
Date Posted: January 01, 2009 at 9:55 AM

Does any one know how to figure out the port length when using 2 ports in one cabinet,I've got a port caculator page bookmarked but it only give the lenght for one port,Don't know if using 2 port if you cut the lenght in half of one port to use 2 or double it?I'm building a bass cabinet for use with a bass guitar and would like to use two ports to prevent chuffing,Ive got an experimental cab right now with one port and it chuggs pretty badly.Figure two ports would help have a four inch port right now can't really go any bigger because of materials

Replies:

Posted By: i am an idiot
Date Posted: January 01, 2009 at 11:08 AM

Can you post the link to the calculator you have bookmarked. Can you give the volume of your box and the desired tuning frequency? You will need to double the area of the port. A 5.65 inch round port has exactly twice the area of 2 4 inch ports. So if you can put in the port size as a 5.65 inch port. Whatever length it comes up with will be the length you need to cut the 2 4 inch ports to.

Posted By: DYohn
Date Posted: January 01, 2009 at 11:24 AM

Each port will more than double in length (for the same tuning frequency) because it's based on the area of the port opening. Two 4" ports is approximately the same area as a single 5.65" port. Calculate the length you would need for a 5.65" port and then both of your 4" ports need to be that long. Example: tuning 3 cuft to 30Hz with a single 4" port = 9.62" long. Using two 4" ports each must be 20.9" long.

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Posted By: DYohn
Date Posted: January 01, 2009 at 11:25 AM

Great minds... posted_image

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Posted By: i am an idiot
Date Posted: January 01, 2009 at 1:06 PM

How many tries did it take you? I did 6 5.75 5.6 and then 5.65

Posted By: reyoung759
Date Posted: January 01, 2009 at 5:16 PM

The port caculator is on this site the 12volt.com.the box volume is 4.47ft3 gross would like to tune to 50hz,don't need any lower frequency,our 4 18" for the front of house sound will take care of the rest thanks again

Posted By: DYohn
Date Posted: January 02, 2009 at 9:59 AM

i am an idiot wrote:

How many tries did it take you? I did 6 5.75 5.6 and then 5.65

I calculated it. 4 X 3.142 = 12.568 X 2 ports = 25.136 sqin port area for dual 4" ports. 25.136 / 3.142 = 8, Sqrt 8 = 2.82. 2.82 X 2 = 5.656 in diameter port. posted_image

4.47 cuft vented at 50Hz = 1.91" long @ 5.65" diameter (or with dual 4" ports.)

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