I have a bass cabinet with a shelf in the middle, ends up being two separate cabinets. Each end's volume is 3.83... considering a few braces better count on 3.75 or so. Now, I need to know what ports to put in it. Most of the online calculators I have seen say that if I want to tune it to 35 Hz, (yes I want it LOW), to use one 4" port that is 4.4" long.

My question is, how is this affected if you put in TWO ports, PER SIDE? Gallien Krueger makes a similar box, and they use four ports, looks like 4", and I am wondering how you calculate this when putting in multiple ports like that. I seriously doubt that you can just take the same exact thing and duplicate it and just get louder results, but I really don't know. I had one calculator tell me that your port tube length increases to over 11" each if you use two ports instead of one that is 4.4" long, which seemed strange.

Worst case I'll just use that one, but I have seen multiple similar 12" neo bass cabs that use two 4" ports per side, for two 12's per side, and I really don't know how they're calculating it. I've been using calculators like this:


This calculator lets you tell it to use multiple ports:


Guess I'm just making sure that I understand correctly, that I basically need four 4" ports that are over 11" long for my 4x12 cabinet, if I used 4 ports instead of 2.
Last edited by corndogggy at Jul 24, 2008,

The second one down calculates port length for multiple ports in the same enclosure.

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Edit: Reduce the diameter of the ports and the vent length will decrease. A 3" port diameter will give you 6.1" length for each port. The wider the port the longer it needs to be. It's very complciated as to why that is and I don't have all day (literally) to write it up. You'll just have to trust me, 3" is the way to go. It's a happy medium.
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Last edited by MeanwiththeDean at Jul 24, 2008,