Hey guys, now i am ongoing building a subwoofer project ...
I need help ... the ports for subwoofer i found locally were too small ..... to make things easy for me to work ..... i know i can use PVC pipes as ports .... but there are no way to make flares for the port ends ....
so therefore considering the use of slot ports came to my mind .... can give advice .... slot port or rounded port is better for subwoofers ....?
I need help ... the ports for subwoofer i found locally were too small ..... to make things easy for me to work ..... i know i can use PVC pipes as ports .... but there are no way to make flares for the port ends ....
so therefore considering the use of slot ports came to my mind .... can give advice .... slot port or rounded port is better for subwoofers ....?
If port air velocity is fairly low there's basically no difference. So usually you'd make a round port because they're easier to make and comes in many ready-made sizes.
If port air velocity is fairly high then a slot port is preferable as port noise will be distributed over a large number of frequencies instead of one frequency as with a round port.
Correctly made slot ports will always be preferable to round ports.
If port air velocity is fairly high then a slot port is preferable as port noise will be distributed over a large number of frequencies instead of one frequency as with a round port.
Correctly made slot ports will always be preferable to round ports.
But round ports have the least internal surface area per unit volume, meaning you should get better efficiency due to less air friction. Whether this difference would be noticable in practice I don't know, but I always use round ports in any case as I find them so easy to install.
If port noise is a problem, perhaps use larger or additional ports as long as you can make them long enough to maintain tuning.
If port noise is a problem, perhaps use larger or additional ports as long as you can make them long enough to maintain tuning.
Correct. And that's another benefit for slot ports. Increased air friction, though meaning less port efficiency, helps dampen unwanted cone excursions below the tuning frequency.
The higher the port air velocity, the better the driver is protected.
Technically post #9 is right. A round port of the same area as a rectangular or slot port will have less air friction and will support higher airspeeds (thus more output) prior to the air flow becoming turbulent and finally further output becoming totally compressed. There is a nice JBL AES study on port behavior.
At the end of the day the real world difference may not amount to a noticeble one and other considerations like cabinet geometry, cost, ease of manufacture, etc, are often more important factors.
At the end of the day the real world difference may not amount to a noticeble one and other considerations like cabinet geometry, cost, ease of manufacture, etc, are often more important factors.
Danny,
A flare serves as an impedance transform, moving from a condition of small volume & high (relative) speed to one of large volume and low speed. The reverse is also true if both ends of the port are flared. They are not strictly necessary. They do provide a region of more gradual transform of the wavefront into the listening area.
Not if the air speed or velocity is low, flares are not needed at all.
Tubular ports are simple to install and calculate. Some choose to increase the diameter or add a second port once the velocity approaches the limits of turbulence, other designs choose to flare a smaller port and hope for the best. Sometimes the lengths of low velocity ports leads to an impracticable situation such as bends and such. You can build slots doing the same thing, but due to geometry, the corrections are more difficult to predict and so final tuning lengths are usually best done with measuring the impedance nulls. Measuring box tuning is best because other errors in drivers, box volume, stuffing etc are managed in one or two port length adjustments.
I use long high ratio slot vents to purposely increase the friction. I find this works very well to improve the quality of the bass. Largerly due to improving the tolerance to the shifting tuning/T-S due to the dynamics of drive levels.
dave
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