DIY: a Subwoofer Calculator for a Dual Port Enclosure
- 1). Design and build a subwoofer cabinet around your subwoofer, using Thiele-Small parameters published for you woofer, and a ported-cabinet calculator. Thiele-Small parameters are electro-mechanical descriptors of any given driver that detail moving mass, suspension stiffness, interaction of the voice coil with the magnet, nominal displacement, and likely reaction to an enclosure.
- 2). Visit the referenced vent dimension calculators. Enter the port type and quantity, enclosure volume, desired tuning frequency and port diameter or cross-section area into the vent length calculator. The port diameter or cross-section area should be a commercially-available product with an inside diameter equal to or greater than the figure derived with the minimum vent diameter calculator.
- 3). Build your ports so that the inside terminus is far enough from the rear wall to keep from restricting air flow: A good rule of thumb is to make that distance at least equal to the radius of the port. The easiest approach is to use PVC pipe, or thick cardboard mailing or carpet tube. If your ports are longer than the cabinet is deep, PVC affords the opportunity to use elbows or U-traps to "bend" the tube. Measure a center line through the bends to maintain proper port length.
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