Over the last few years I've built a number of speakers, all have used a round port because most of the info I've found to date suggests that round is better. I'm starting a new project and have an itch to build my own rectangular port...but will I be disappointed?
Any feedback will be most appreciated.
Any feedback will be most appreciated.
No, as long as the port's aspect ratio is not overly large which could cause "noise" because of the large "circumference" from a really narrow slot. Some people recommend an aspect ratio not exceeding 5:1 or so, but that may be unnecessarily restrictive. The peak air velocity in a port, which is the primary source of chuffing or noise, depends on the port's area, but as a port moves from round, to square to being a slot, all with the same area, the port's circumference becomes larger and larger, presenting more and more of an edge to cause turbulence. Others may disagree but I'm currently listening to my latest build which has twin slot ports, each 1" x 2", which has no discernible port-related issues.
Paul
Paul
You should build quick and dirty prototype box with both ports and test it out! If there is a difference, you are able to choose the better one and can then move on to worry some other compromise. Have fun! 🙂
A slotted port is different to a rectangular port. Which one are you considering, as your post mentions both?
For clarification, when I said slotted or slot port, I really meant a rectangular port.
Paul
Paul
I'm considering a rectangular port, the dimensions at present are 1.5" x 8" x 10.25" deep. This dimension theoretically will deliver 30 cycles.
funny i should come across this thread as i was just recently discussing this very thing with an old guitar player buddy of mine.
the Theile 12 guitar cab with slot port, originally designed for an EVM 12 L and i was wondering if i could find the original plans....then he sends me a link to this 1x12 Front Ported Thiele Guitar Amplifier Cabinet | MESA/Boogie(R)
the Theile 12 guitar cab with slot port, originally designed for an EVM 12 L and i was wondering if i could find the original plans....then he sends me a link to this 1x12 Front Ported Thiele Guitar Amplifier Cabinet | MESA/Boogie(R)
Ok, I've decided to go with the slotted port. When calculating the internal speaker volume do you factor the internal area used by the port and add that?
The BEST Port Video EVER - YouTube
I have built both, unless you have a space restriction necessitating a square port I would stick with a round port, audio results are (sometimes) better with less issues. Slot ratio (H to W) is also important if your going with a rectangular port.
I have built both, unless you have a space restriction necessitating a square port I would stick with a round port, audio results are (sometimes) better with less issues. Slot ratio (H to W) is also important if your going with a rectangular port.
Yes. Internal volume (as in the air spring behind the speaker and the port) comprises only of the air inside. So no ports, no speaker magnet, frame or cone, no bracings. One exception: the acoustic lining. Acoustic lining actually 'weakens' the air spring a bit, the internal volume appears somewhat bigger than without the lining. But that is only marginal.
As for ports and slots, two other considerations: chuffing noise almost always is caused by sharp edges of the port. Chamfer or roundover the port ends. With rectangular ports this is even more important.
And: try to execute a port with symmetrical ends, that including the surrounds. This will prevent the enclosure pumping up at prolonged sounds because of uneven air flows in and out the port, which in turn will bring the driver out of it's equilibrium and thereby causes higher distortions.
sorry to interrupt but before we debate slot versus round would it not be better to ask the OP what his goals are? is this a speaker that's intended for reproduction or an MI (musical instrument cab)?
sorry it's just that i realized that my earlier contribution to this thread maybe not be inline with the intent of this thread.
sorry it's just that i realized that my earlier contribution to this thread maybe not be inline with the intent of this thread.
The slot port reminds me of taking a handful of drinking straws and setting them into a round port, which is an old technique, and it slightly changes the tuning.
If the port wasn't so small acoustically there might be benefits to distributing its output.pkitt said:
Can we be clear that the OP is making a 'rectangular port'?
I understand that a 'slot port' uses an internal wall of the cabinet as part of the port - this side therefore extending beyond the end of the port.
See the bottom right enclosure in the attachment.
I understand that a 'slot port' uses an internal wall of the cabinet as part of the port - this side therefore extending beyond the end of the port.
See the bottom right enclosure in the attachment.
Attachments
Hi folks,
Thanks for all the help, much appreciated!
It is definitely a slotted port, in that the outer walls of the speaker cabinet will become part of the port.
As to why I'm interested in a slotted port vs a round port - perceived performance and aesthetics. Assuming properly radiused corners, my experience with speakers built by others that used a slotted port was that the bass was more detailed and tuneful. Is it just because of the slotted port? I don't know. As for the aesthetics of a slotted port, it just looks cool to me.
The speaker that I'm building is actually a rebuild of a speaker I purchased in 1984 as a bookshelf. The new cabinets will be floor standers with huge spikes, the drawing I've made with a slotted port really just seems to make the speaker look more the business. The bass driver will be isolated from the mid and tweeter, so the speaker gets noticeably deeper as well. Since I will likely look at them the rest of my days I may as well feel good about it.
I spent 3 years modifying the crossovers and have them to a point where I'm very happy, so I'm in the home stretch.
Thanks for all the help, much appreciated!
It is definitely a slotted port, in that the outer walls of the speaker cabinet will become part of the port.
As to why I'm interested in a slotted port vs a round port - perceived performance and aesthetics. Assuming properly radiused corners, my experience with speakers built by others that used a slotted port was that the bass was more detailed and tuneful. Is it just because of the slotted port? I don't know. As for the aesthetics of a slotted port, it just looks cool to me.
The speaker that I'm building is actually a rebuild of a speaker I purchased in 1984 as a bookshelf. The new cabinets will be floor standers with huge spikes, the drawing I've made with a slotted port really just seems to make the speaker look more the business. The bass driver will be isolated from the mid and tweeter, so the speaker gets noticeably deeper as well. Since I will likely look at them the rest of my days I may as well feel good about it.
I spent 3 years modifying the crossovers and have them to a point where I'm very happy, so I'm in the home stretch.
I'm not sure of what magnitude it will make an impact, but a round port will have the least surface area for it's volume so it will flow better, and sharp corners will probably not flow much at all.
It's also like Galu showed, the exact point of where the port begins inside the box will be somewhat diffuse.
So if you can, make the port so you can fine tune it.
It's also like Galu showed, the exact point of where the port begins inside the box will be somewhat diffuse.
So if you can, make the port so you can fine tune it.
I don't think circular vs. rectangular makes a difference. The important thing for the bass-reflex tuning is the mass of air in the port, and the cross sectional area that couples that mass to the internal volume of the box.
That said, I still think that many implementations of rectangular ports do indeed perform differently than round ones. However, this is not related to the basics of the bass-reflex principle, but rather to how / where in the box the ports are implemented. The easiest way to make a rectangular port is by inserting a separator panel near the bottom or top of the box. This means that rectangular ports tend to be at the bottom or top of the box. This is different with round ports, which are easy to do everywhere in the box. In my opinion, it's better to keep the port away from the bottom/top ends of the box in order to avoid coupling the port to the pressure nodes of the standing waves in the box. This means that ports should go near the center of the box, which I find easier to do with a round tube.
That said, I still think that many implementations of rectangular ports do indeed perform differently than round ones. However, this is not related to the basics of the bass-reflex principle, but rather to how / where in the box the ports are implemented. The easiest way to make a rectangular port is by inserting a separator panel near the bottom or top of the box. This means that rectangular ports tend to be at the bottom or top of the box. This is different with round ports, which are easy to do everywhere in the box. In my opinion, it's better to keep the port away from the bottom/top ends of the box in order to avoid coupling the port to the pressure nodes of the standing waves in the box. This means that ports should go near the center of the box, which I find easier to do with a round tube.
