need help with subtraction of port
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=12141
Printed Date: May 15, 2025 at 5:52 PM
Topic: need help with subtraction of port
Posted By: flaneledholes
Subject: need help with subtraction of port
Date Posted: April 13, 2003 at 12:49 PM
Hello all, it has been a while since I have needed help, but I have my box volume at 1.479cuft ... that is with all the bracing and driver included, so after all that trouble, I do not know how to subtract my port, my port is 3 inches in diameter, and 17.5 inches in lenght... If some one could tell me what the volume of my port is or give me a link to an online calculator, it would be greatly appreciated!
thank you for your trouble
Replies:
Posted By: flaneledholes
Date Posted: April 13, 2003 at 3:23 PM
bump
Posted By: flaneledholes
Date Posted: April 13, 2003 at 4:02 PM
well, I did a search and found what I was needing, but my next question is, does it matter where I put the port tube at? I was wanting to put the port tube on the side, while the sub sits on the top... Imagine a square box, and the sub ob top, and the port tube on the bottom, would this make a diference in the outcome? thank you so much.
Posted By: Tcole
Date Posted: April 13, 2003 at 5:26 PM
All is good as long as the port output isnt restricted by the surface it is firing against.
Hope that helps
Posted By: flaneledholes
Date Posted: April 13, 2003 at 6:25 PM
that answers all of my questions, thank you so much!
Posted By: x6369x
Date Posted: April 14, 2003 at 8:01 AM
The volume for a cylinder/port is (pi)(r*r)(h). Where:
pi=3.14,
d=3, r=d/2=1.5, so r*r=2.25,
h=l=17.5
So the final cylinder/port volume is 123.68 cu inches, or 0.072 cu ft.
You net box volume will be 1.479-0.072=1.407 cu ft.
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