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PORT Size Calculations and Formulas for WOOFER and Subwoofer BOXES

Vent Dimensions Calculator

Minimum Usable Vent Diameter
 The first thing you should do when calculating a vent is to determine how big it has to be. "Port noise" can ruin the sound of an otherwise good enclosure design. If you do not have the Xmax figure for your driver(s), leave the default value (it is an average value suitable for most subwoofers).

 If you want to use this calculator, first choose what size driver(s) you are using, then enter how many are in your enclosure. Now, enter your Xmax figure (in millimeters), and the frequency that you need to tune your vent to. And, finally click the "Calculate Minimum" button to get your results. The "Minimum Diameter" box is for round ports, and the "Minimum Area" box is the minimum area required for a square vent. If you need to convert a measurement to/from English/Metric click here, then come back.

Driver Size (Inches)
6.5 1012 15 18
Is this a bandpass enclosure?
No  Yes
Enter Quantity of Drivers 
Enter Xmax mm
Enter Tuning Frequency Hertz
Minimum Diameter =  inches
Minimum Area = inches

Length of a side
for a square vent =
Calculate Your Vent Length

 To use this calculator, first you will need to choose whether you want a round or a square port. Then, enter your internal box volume (in cubic feet).

 Next, you enter either an inside diameter for the tube you are using if you want a circular port, or the inside dimensions of the square port you are going to build into your box (make sure you click the "Slot Port" button if you are designing a slot port - if you don't understand the difference between a square vent and a slot vent, click here). And finally, press the "Calculate Length" button at the bottom, and your answer will appear in the "Vent Length" box.

Select Your Port Type
Round  Square 
Is this a slot port ?
No  Yes 
Quantity of ports
Enter Enclosure Volume (ft3 )
Enter Desired Tuning Frequency  Hertz
Round Vent
Enter Desired Port Diameter
Square Vent
Enter Height
Enter Width Inches
Vent Length  Inches
  If you come up with a value too long for your enclosure, enter a smaller number(s) for the diameter, or the heighth/width of your vent(s), and click the "Calculate Length" button again to recalculate (you don't need to reload the page).


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