# calculating ports resonating fq.

Discussion in 'Archived Threads 2001-2004' started by AlexKunec, Jun 6, 2002.

1. ### AlexKunec Stunt Coordinator

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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....?

2. ### Ron Shaw Stunt Coordinator

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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. ### Chris Tsutsui Screenwriter

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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.

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