External ports/ air volume pressure/ box rise

[Minideathray]

hello all,

Building a spl burp system in a Daewoo. Two 18s 6 cub box. Want to use exterior port to max box internal space. When figuring port length wouldn't the square inches of the port be ADDED to the box size? since it is on the outside of the box. Also i was reading that the size of the port directly relates to air flow volume. The larger the port the slower the volume speed. Which decreases box rise. Any thoughts???

[stipek]

You are concerned with net box volume, with the port outside the box the net volume will always be the same. Makes it easier to calculate your desired frequency and port volume because the net volume is constant. With an internal port, the port volume is subtracted to get a net volume and then that figure is used to determine tuning frequency. There can even be ports with some of it inside the box and some sticking out which makes the calculation a little more complex.

Port area does affect the air speed but there is a balance....min and max. Port opening too big well you just have a big hole in the box, port too smalll and you basically have a leaky sealed box because the air compresses and goes back inside the box.