How to Tune a Vented Subwoofer Enclosure
After you have built a cabinet using Thiele-Small parameters for a vented design for your particular woofer, it is time to add and tune the vent. Using internet calculators for the proper cabinet size, vent cross-section and length, use PVC pipe, stiff cardboard carpet tube or wood fashioned into a square or rectangular vent to tune your speaker. Tuning is largely a matter of cutting or building a vent with the right total volume to work with your cabinet and speaker sizes and desired tuning frequency, so your precalculations will eliminate trial and error.
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Things You'll Need
- Saber saw or circle cutter
- Hack saw
- Circular saw
- 1-1/2 inch drywall screws
- Drill
- Countersink bit
- Gorilla glue
- Wood rasp
Instructions
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1
Use an Internet port size calculator (see Resources) and plug in your speaker size, cabinet volume, desired tuning frequency, and driver xmax. Xmax is the maximum distance the cone can travel linearly (comfortably) in one direction from rest position, in millimeters. Ports can make wheezing sounds if they are too small in cross-section or diameter, so pay attention to the minimum diameter.
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2
Decide whether you want a round or a square vent. Round vents are generally easier to construct, since pipe or tubing does not have to be built, only cut to length and installed. The distance the inside-cabinet end of the port is from the wall where it terminates should be at least equal to the vent's inside radius, or half the wall-to-wall measurement.
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3
Cut PVC pipe or carpet tubing with a hack saw, or build a square vent with the same material you used to build your cabinet using a circular saw, screws and glue. Use the calculated length (from Step 1) for the inside diameter or square area of the vent and the inside cabinet dimensions to position the vent.
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4
Use a saber saw or hole cutter to make a hole in the front baffle of the speaker cabinet to fit your vent. Make the hole slightly too small at first, then use a wood rasp to shape the hole little by little until the vent fits tightly. Apply glue and re-fit the vent with its terminating edge flush with the baffle surface and allow to dry overnight. For a long vent, you can brace the other end for strength.
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Tips & Warnings
The vent termination to the outside can be placed anywhere on the front of the speaker cabinet. If the calculated vent is too long for the cabinet depth, use an elbow at one end of the vent to terminate it to the outside and install the vent along the longest dimension of the cabinet. The center line through the elbow is part of the total vent length.
References
- Photo Credit speaker image by askthegeek from Fotolia.com
