slot port dimensions

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=117710
Printed Date: July 12, 2025 at 8:14 AM

Topic: slot port dimensions

Posted By: adelphia83
Subject: slot port dimensions
Date Posted: November 13, 2009 at 3:51 PM

I'm going to be building my own 12" ported enclosure for an RE Audio SX12 subwoofer. I need it to be around 3 cf, tuned to about 34hz.

I'm working with the enclosure calculator to figure out my port dimensions and it's asking me the box volume. I figure it's a given that this is the box volume minus the volume of the subwoofer inside it, but what about the port? Do I need to subtract the volume of the port? Of course I don't know the port volume yet without know its dimensions.

So far the box will be about 30W x 17H x 14W. I'd like the port to be vertical and come out the front left. When I figure the length of the port into the box, is it okay to turn the port 90 degrees if the depth isn't long enough to accommodate the port? Does this change anything? Sorry for the novice questions.

Replies:

Posted By: j.reed
Date Posted: November 13, 2009 at 4:39 PM

Yes you need to subtract the port and any internal bracing as well.

Also yes you can fold the port. Here is a link to a good resource. It shows you how to properly fold a port. And also how to make it accurate length when folding. https://kicker.com/box_building_hints

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Posted By: stevdart
Date Posted: November 13, 2009 at 10:33 PM

You're right that you can't subtract a port volume whose dimensions you don't yet know. But you're not really subtracting anything at this point; you are providing a net volume goal with which to work. The volume of the box is always net, which is nothing but air that is dedicated for the use of the woofer. The port is a separate enclosure; its volume is not nearly as important as its dimensions.

You should end up doing the calculations several times as you work this out to fit your space requirements. This is because the port and all its baggage (extra walls) does amount to a volume, and that volume takes up space in your project which leaves less room for net air. So thus the dance back and forth as you have to recalculate shrunken net airspace and refigured port dimensions, until you compromise it all into your given space and everything fits.

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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.