looking for formula
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=38952
Printed Date: May 17, 2024 at 11:28 PM
Topic: looking for formula
Posted By: gcorrea
Subject: looking for formula
Date Posted: September 10, 2004 at 9:22 PM
looking for formula on calculating dual ports for a sub box. anyone know it or a site where i might find it.
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gcorrea
Replies:
Posted By: auex
Date Posted: September 10, 2004 at 9:23 PM
Calculating what about the ports exactly?
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Certified Security Specialist
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I promise to be good.
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Posted By: 12-volt_guy
Date Posted: September 10, 2004 at 9:34 PM
Here is a site with an online calculator: -------------
Posted By: gcorrea
Date Posted: September 10, 2004 at 9:37 PM
tuning frequency, if i use a single 4 inch port my port will be about 25 to 30 inches long to achive my desired frequency and since the front of my box is about 14 inches from the back i figured i can use dual 4 inch ports. insted of getting a 90 degree elbow for the pvc and running them through the box.
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gcorrea
Posted By: auex
Date Posted: September 10, 2004 at 9:56 PM
It is not as simple as you make it sound. Using 2 ports will actually make both ports longer. Lets say you are using a JL 10W0-12 in a 2 cubic ft box, with 2 subs, tuning to 45hz. If you use 1 4" port it will need to be 5.47" long. If you use 2 4" ports then both will need to be 13.88" long. If for some reason you used three then all ports would need to be 22.29" long.
This type of calculation needs to be done with a box building calc or program. I could probably dig up the formulas, but there are bunch of them and it is just easier to use WinISD or like.
-------------
Certified Security Specialist
Always check info with a digital multimeter.
I promise to be good.
Tell Darwin I sent you.
I've been sick lately, sorry I won't be on much.
Posted By: 12-volt_guy
Date Posted: September 10, 2004 at 10:00 PM
Another optioin is to build in a rectangular port. The equivalent for a 4" diameter 25" tube port in a rectangular shape would be around: 15.75" wide x 2" high x 10" deep -------------
Posted By: 12-volt_guy
Date Posted: September 10, 2004 at 10:06 PM
To formulize this: Port area = Pi(radius^2) x Length or 3.14159 x 4 x 25 = 314.159 Rectangular Port = 15.75 x 2 x 10 = 315.00 -------------
Posted By: gcorrea
Date Posted: September 10, 2004 at 11:02 PM
i got the blaubox program and the winisd. because of the shape of my box slot porting would be difficult. ------------- gcorrea
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