caculating ports

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reyoung759

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Joined: January 01, 2009

Location: Ohio, United States

Posted: January 01, 2009 at 9:55 AM / IP Logged

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

i am an idiot

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Joined: September 21, 2006

Location: Louisiana, United States

Posted: January 01, 2009 at 11:08 AM / IP Logged

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.

DYohn

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Joined: April 22, 2003

Location: Arizona, United States

Posted: January 01, 2009 at 11:24 AM / IP Logged

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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DYohn

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Posted: January 01, 2009 at 11:25 AM / IP Logged

Great minds... caculating ports -- posted image.

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i am an idiot

Platinum - Posts: 13,671

Joined: September 21, 2006

Location: Louisiana, United States

Posted: January 01, 2009 at 1:06 PM / IP Logged

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

reyoung759

Member - Posts: 2

Joined: January 01, 2009

Location: Ohio, United States

Posted: January 01, 2009 at 5:16 PM / IP Logged

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

DYohn

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Posted: January 02, 2009 at 9:59 AM / IP Logged

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. caculating ports -- posted image.

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

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caculating ports

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