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Old 11-01-2008, 03:42 PM   #1
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How to calculate a slot ported box

Here is how to build a simple slot ported box with 1 90 degree bend. First, determine the ideal specs of the sub. I wouldn't use modeling programs. The best info will come directly from the manufacturer's tech dept. They should have a LOT of experience with the sub in different size boxes and tuning freqs.

Net internal volume. You need to know if this accounts for the sub itself which becomes important in smaller boxes since the speaker accounts for a more significant % of the gross int volume.

Tuning Frequency. Expressed in Hz. Usually you want to keep in the low 30's (30hz-35hz) but the best freq will be determined by the sub and the listener's preferences.

First, determine the port area needed. General rule is 12-16 sq in per cu ft of int volume to avoid port noise. So if you have a 1.5 cu ft net int volume box, you would want 18-24 sq in of port area.

Here is a link to help you out.


Once you know what your target range is for port area, then start plugging in the numbers in the link below.


Basically, just play with the red numbers until the box volume (ft3) and Tuned Frequency (Fb) are real close to the spec for the sub. Its trial and error.

Below, you'll get all of the required cuts to build your box.

JUST MAKE SURE YOU HAVE ENOUGH ROOM TO MOUNT THE SPEAKER! If you are building a box for a 12" sub and all of your dimensions are 10", it won't work.

Also keep in mind that the side 2 of the port might run behind the speaker mounting location. Make sure you have enough mounting depth when you take the port width into account.
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Old 12-19-2009, 05:49 PM   #2
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I used this (http://reaudio.com/speaker_box/LPort_Box_Calc.html) program to build a box for my 330ci and the box is huge. I managed to get 1.7 cu feet per 12" speaker and 2 12s tuned to 27hz which is what i guess the type rs are supposed to be tuned to and let me tell you this HUGE DIFFERENCE!!! It was day and night. Thanks for the info about the box setup bigjae1976. All I need now is some sound dampening to get what i paid for out of the system.
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Old 12-19-2009, 07:02 PM   #3
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Glad to hear it worked out for you.
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Old 01-03-2010, 03:51 PM   #4
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I was folowing the instruction in this site

, I use the encloser box for sub. and it gives me a great sound even with stock head unit. I cant imagin the sound if I'm using after market head unit?!.
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