###### Question

# Port dimension calculation query

About to cut dual slot ports into 19l boxes using calculation of speakerboxlite app.

Noticed JLaudio say:

**Multiple Ports**

There are two widely used methods for calculating multiple ports for a single chamber. Only one method is correct, but, unfortunately, it is the least commonly used.

The first and incorrect method takes its thinking from the original port formula and basically says that if we take two ports and sum their cross-sectional areas, we can just plug this total into the port formula for Av to get our port length. This would sound reasonable, but it can lead to serious mis-tunings in some cases, as we'll see in an example below.

The second and correct way to figure out how long each port should be follows this simple three-step procedure:

- Divide the chamber volume by the number of ports you wish to use for that one chamber.
- Take the quotient and use that as your Vb (box volume) in the port formula.
- Do the number crunching and figure out how long each port should be.

Is this notion used in app calculation or not?

Thanks.