**Re: How to calcualate Precision Port in boxnotes?**
Exodus audio has a

page for the Tempest-X that includes an

application guide.

The guide suggests the following ported boxes:

8.5 cu.ft / 19hz

10.6 cu.ft / 17hz

12 cu.ft / 16hz

Assuming you wish to build the 12 cu.ft / 16hz design......

Modelling this in WinISD shows that the Effective length for a 6inch port is 20.31 inches (one end flanged)

The PSP calculator will tell you 20.41 inches for the "Straight Length Port required", which is the effective length.

Going over to boxnotes, enter a port length of 20.31 plus 0.5 ie 20.81, calculated as shown in the earlier posting.

Play around with the internal volume until you get a Working Volume of 12 cu.ft

You should come up with around 12.66 cu.ft for the internal volume.

Notice that the tuning frequency is now displayed as 15.8hz, not 16hz

This is because boxnotes is not taking into account the flare when determining the tuning. This method is giving an accurate volume for the port though.

You can now mess around with the external dimensions (one at a time) to get the shape for the box.

Your Physical length for the port will be

20.31 + 1 = 21.31 inches according to winisd, or

21.41 inches according to the PSP calculator. A variation of 0.1 inches isn't going to make any discernable difference.