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Long Port options

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.....

 

Run external ports

Wrap 'em around the outside!
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!
See more on the Sidewinder sub

 

Fold the port up inside the box

Snorkel ports!
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
See more on the Snorky sub

 

Build a concentric port

DIY Concentric Port
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
See my notes

 

Use a Spiral port

Genelec Enclosure with Spiral Vent
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.
See more on Genelec Subs (offsite link)

 

Build rectangular port into the box walls

Drawing of slot port
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
See more on Slot port flaring

 

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
See more on smoothing rings

 

Use port flares

DIY moulded port
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!
See more on Port Flares

 

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.

 

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

 

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!

 

You can help to improve this site - use the feature request page to suggest changes to content or navigation.      Updated 23rd Januiary 2010