how to measure ports properly

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=113474
Printed Date: May 14, 2025 at 11:51 AM

Topic: how to measure ports properly

Posted By: bigrank916
Subject: how to measure ports properly
Date Posted: April 28, 2009 at 9:10 PM

how do you measure port length? Is it from end to end or from the inside of the box to the end? Im trying to get from 28hz to 33hz and cut my ports (2"x4") according to the info in the port calculations page. Im trying to get away from such low frequency bass and cut my ports considerably but it still is too low. Any ideas?

Replies:

Posted By: bigrank916
Date Posted: April 28, 2009 at 9:23 PM

oh ya...I have 4 hertz 12s in a 91 silverado pushed by a PG tantrum 1200.1. The boxes are approximately 2.01cuft. each.

Posted By: cutlass013
Date Posted: May 02, 2009 at 12:40 AM

maybe someone can back me up but if its round i would think 2" diameter and the 4" length .. if square then ur missing a demension?

Posted By: boogeyman
Date Posted: May 02, 2009 at 10:13 AM

you measure from end to end

Posted By: aznboi3644
Date Posted: May 02, 2009 at 1:04 PM

2 inch port is not enough....atleast a 4" round port

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Custom Enclosure Design

Posted By: bigrank916
Date Posted: May 02, 2009 at 8:01 PM

Yes it is a round port. A 4" port would require a 12.5" length if tuned to 33hz. I thought 4" was too big for a 12" woofer as well. I have two 15s in a box just slightly bigger than this one with ports at 2 9/16" diameter by about 4" length and the same frequency and it sounds perfect. It is in a geo metro though so that probably has a lot to do with it. Im just a little confused why a 2" port is not big enough. I thought it is all the same if the calculations are right.

Posted By: aznboi3644
Date Posted: May 02, 2009 at 8:24 PM

why...not enough port area. Simple as that. A small port with a large woofer will suffer from port compression with much less power than the proper port area. Essentially you will get port noise and the enclosure will act as a very leaky "sealed" enclosure and not like a bass reflex at all.

For each 12" subwoofer I recommend atleast a 4" round port.

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Custom Enclosure Design

Posted By: stevdart
Date Posted: May 03, 2009 at 10:12 AM

Re: your question of measuring port length:

The thickness of the face baffle of the enclosure (where the port extends through) will be included in the measurement of port length.

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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

Posted By: bigrank916
Date Posted: May 03, 2009 at 12:37 PM

Ok. I think I will go up in port diameter. Now knowing the right way to measure it I should get this solved now. Thanks guys for the help.