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# calculating ports resonating fq.

3 replies to this topic

### #1 of 4 OFFLINEAlexKunec

AlexKunec

Stunt Coordinator

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• Join Date: Mar 09 2002

Posted June 06 2002 - 05:11 AM

I am making a sonosub with a tempest driver and 2 4" ports. I want to make some kind of a flare on the ends using wood/router and i was wondering how this would alter the tuning frequency. Is there some formula to find fs given volume, T/S, port area, port volume, etc....?
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1000w crown power amp \$400
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### #2 of 4 OFFLINERon Shaw

Ron Shaw

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Posted June 07 2002 - 03:00 AM

The formula for calculating port length is: Lv=((2.36 x 10^4)dv^2/fb^2 x Vb))-0.74dv Where Lv is duct length and dv is diameter of port. If your port is going to be rectangular, just translate the area into the equivalent diameter for the calculations.

### #3 of 4 OFFLINEChris Tsutsui

Chris Tsutsui

Screenwriter

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Posted June 07 2002 - 07:28 AM

The flared portion shouldn't be measured in the equation. It is the cylinder portion only that equates to the length of the port. At least that's how I calculated it. Imagine if a sub had a variable length port that changed as it played. Then the bass might sound like digeridoo or something.

### #4 of 4 OFFLINERon D Core

Ron D Core

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Posted June 07 2002 - 09:27 AM

You can try to mess with it, but why bother, there is no way you would hear the difference. It would only have to be changed a fraction of an inch. If I were you, I wouldn't sweat it, just enjoy the reduction in port noise and show your friends how cool it looks.

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