SLOT PORTS OR ROUND PORTS .... which is better ...?

[dannyjmf]

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 ....?

[Ed LaFontaine]

I prefer slots for the ease with which I can build any x-sectional area with expansions on each end.

[Top Shelf]

+2 for slots and if you make them big enuf ,don't have to worry about flaring to the extreme.
I think parts express sells flared ends for ABS pipe

[tinitus]

hmm

how about triangular ports, in the corners ?

[sofaspud]

"hmm" is right. I think that's an interesting concept there, tinitus. I can easily imagine pluses when it comes to aesthetics and diy.

[infinia]

it's all a trade off
* lower cross sectional area means shorter length, at the expense of high air movement thus turbulent noise ie flares.
* slots can be built with higher area but have longish lengths for the same tunings.
calculate the air speeds for each to decide

[dannyjmf]

If using slot ports .... is it necessary to flare the end slightly .... to avoid port noise .....

[Saturnus]

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.

[Andy Westcott]

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.

[Saturnus]

Originally Posted by Andy Westcott

But round ports have the least internal surface area per unit volume, meaning you should get better efficiency due to less air friction.

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.