port length

Printed From: the12volt.com
Forum Name: Car Audio
Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=104337
Printed Date: July 06, 2025 at 8:13 AM

Topic: port length

Posted By: sesh1975
Subject: port length
Date Posted: April 28, 2008 at 2:40 PM

Hi guys! I need your help please. I have used the port calculator on this site but I want to make sure that its absolutly on the money. I have a fiberglass enclosure with 2.8 cubic feet per sub. Im going to use a 4" port and Im trying to get it tuned to 34.5Hz. What is the proper port length???

Thank you

Replies:

Posted By: DYohn
Date Posted: April 28, 2008 at 2:55 PM

The port length calculator on this site will give you accurate results.

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Posted By: sesh1975
Date Posted: April 28, 2008 at 3:01 PM

I have been getting mixed results. I have used a few other calcs and they come in at a minimum of 2 4" ports at 16" in length. Im just trying to get it right the first time.

Posted By: taylormade1975
Date Posted: April 28, 2008 at 3:17 PM

7.23565 inches long

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Posted By: stevdart
Date Posted: April 28, 2008 at 9:16 PM

You should probably arrive at port opening size of no less than one 4" port per sub (12.6 sq in), and you may need to go bigger than that. If you are designing a dual sub enclosure, double the port opening size or double the number of ports. Either way you do it, for the same tuning frequency the port length will calculate to roughly double the length.

According to your posts, and taylormade1975's answer, it sounds like you are getting proper results.

Note: a 6" diameter port is more than double the opening area of a 4" port.

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Posted By: sesh1975
Date Posted: April 28, 2008 at 10:56 PM

Lets keep this easy. Im designing this for a single 12" sub. I know from the material that came with the sub that Im designing to meet the 34.5Hz. I know that my Xmax is 20.5mm. I have 2,8 cubic feet and I really only have enough room for a single port that will run parrallel with the sub. 4" is the max diameter I can go with the port. So is the 7.2 length still correct?

Posted By: daboss593
Date Posted: April 29, 2008 at 10:16 AM

i just had my box made for my 1252w infinities and thought the guy messed it up. 2 cbs per sub and the vented ports are enormous as in length not diameter. but he called infinity and was assured the specs are right this is a 30-32 hz box. then again this is the 1st time ive had some decent entry lvl stuff. and not junk lol

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Posted By: boogeyman
Date Posted: April 29, 2008 at 9:16 PM

1 sub-2.8 cubic feet - 4" port 34.5 hz = 7.23565 port length.

Posted By: sesh1975
Date Posted: April 30, 2008 at 11:08 AM

Thank you all for the help. Finally got it figured. We can lock this one up now. '

Shawn