# How to calculate the port length of a subwoofer box

Written by micah mcdunnigan
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Subwoofers add depth and bass to the sounds playing through your speaker system. One way to improve a subwoofer's sound is to add ports into your subwoofer box -- tubes that pipe sound from inside the box. By default, manufacturers seal subwoofer boxes before they are shipped out. However, if you are building your own subwoofer or looking to modify your current one, you can install these ports yourself. Acoustics are a precise matter, so you will need to carefully calculate the ideal port length for your subwoofer.

Skill level:
Moderate

### Things you need

• measuring tape

## Instructions

1. 1

Measure the width, height and depth of your subwoofer box, in inches. Multiply the three values together to determine your subwoofer box's volume in cubic inches.

2. 2

Measure the diameter of the port tube you want to install in your subwoofer box, in inches. This is the distance from one edge of the circle to the point exactly opposite it.

3. 3

Decide what tuning frequency you want to tune your port to. A port tuning frequency of 45 hertz (Hz) will produce a louder but lower-quality sound. A lower tuning frequency, of around 25 Hz, will be more muted but produce a higher-quality sound with lower audible notes.

4. 4

Calculate the port length for your subwoofer box using the following equation: ((14630000(diameter/2)(diameter/2))/((frequencyfrequencyvolume1728)-(1463(diameter/2)))). In this equation, diameter is the diameter in inches of the port tube you measured in Step 2; volume is the volume of your subwoofer box in cubic inches that you measured in Step 1; and frequency is the tuning frequency in hertz that you chose in Step 3. The answer to this equation will be in inches.

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