Run external ports
As shown elsewhere on this site, external ports can be employed where you are happy to have a sub that doesn't disappear into the decor. Great conversation starter!
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Some suggestions for when the port length is greater than the box size When a ported subwoofer is tuned low, and uses ports large enough to keep airspeed to a reasonable level, the result can be long ports. Here are a few ideas to help you deal with them..... |
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Run external ports As shown elsewhere on this site, external ports can be employed where you are happy to have a sub that doesn't disappear into the decor. Great conversation starter! |
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Fold the port up inside the box For a conventional looking sub, you can try this arrangement. Do your measurements carefully to leave room for the driver and amp. Here a shelf brace doubles as a bracket to hold the ports. This is a box with an internal height of 680mm containing a pair of 823mm vents |
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I experimented with one of these - after much construction and testing, I found that it was far too noisy. The changes in direction of the airflow and boundary effects from the increased circumference proved too much. Someone else might be able to refine the design to make it workable |
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Use a Spiral port For advanced constructors only! This is the solution adopted by Genelec, who make high output subs for commercial use. The port is made from metal sheet, and doubles as the sides of the enclosure. |
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Build rectangular port into the box walls For those of us who are less handy with metalwork, a similar solution can be done in wood. Slot ports have been around for a while in the pro-sound world and even some commercial HT subs have them
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Flange both ends of your port The "end effect" means a slightly shorter port is required. You should be doing this anyway! If you are unable to flange the port intake, consider installing a smoothing ring |
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Use port flares Less turbulence means a smaller diameter port can be used - which means a shorter vent. You can use commercial flares or make your own. They really make a difference! |
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Increase box size slightly For a given tuning frequency, as box volume increases, the port length decreases. This option increases air velocity, so careful modelling is needed. Worth exploring if a modest saving in length saves having to use a bend in your port. |
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Lower tuning frequency slightly Port airspeed varies with frequency and peaks at the tuning frequency. For borderline designs, dropping tuning a little may decrease velocity enough to allow a smaller diameter port, which will be shorter
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Here's an idea for some fun... |
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It might be possible to somehow apply the B&W "Flowport" treatment, adding dimples to the port flare to further minimise turbulence. There have been some interesting claims in regard to savings achievable. Although no doubt biased, here's a pdf paper from B&W on dimples Some strips could be cut from a "Sprite" soft drink bottle and used dimple experiments.... Postscript: According to an AES study, (Maximising Performance from Loudspeaker Ports), encouraging turbulence in the boundary layer is of most benefit where the main airlow is already turbulent. This would suggest that whilst dimples are good for golfballs, they aren't much use for quiet ports. |
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If you think some of these designs are convoluted, you'll be amazed at the
folded horn gallery at fullrangedriver.com |
Surely with all these options you'll never get a port noise complaint ever again!
Last update to this page 1st February 2008
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