How to Determine the Port Size on a Speaker Box

By Bob White

A correctly sized speaker port will enhance the low end sounds.
i 3 way Speaker image by Edward Stephens from

A speaker enclosure, or speaker box, can enhance the low end frequencies of speakers if it is properly sized and built. Speaker manufacturers will provide the necessary information within the owner's manual to construct such a box. The box's port can be almost any shape; typically builders use PVC piping to create these systems, so they are generally round. Sizing the diameter and length of the pipe involves a complex math equation. If you have the required information on hand you can use a online calculator to do the hard work.

Record the necessary information to calculated the port size from the speaker's owner manual. You will need to know the driver's size, number of drivers, Xmax, tuning frequency and enclosure volume.

Turn on your computer and open an Internet browser. Cut and paste the following link into the browsers address bar and hit enter:

Calculate the vent diameter by entering the required information in the fields and hitting the "Calculate Minimum" button. Your results will be displayed beside the content you entered.

Calculate the vent length by entering the required information in the fields and hitting the "Calculate Length" button. The vent length will be displayed above the button.

Take these measurements and purchase venting material that meets the size requirements for your port.