# Slot or Circle Port?



## ErinH (Feb 14, 2007)

I’m curious as to why you chose it.

I like circle ports for ease of installs and the fact that tuning is made simpler if you decide you want to change it. Not to mention they are lighter. I have actually heard that slot ports are more efficient, but I have no idea why. Assuming the same cross sectional area, I don’t know what benefits sound-wise one would have over the other.


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## chad (Jun 30, 2005)

Circle, I have a hard time finding square PVC


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## ErinH (Feb 14, 2007)

chad said:


> Circle, I have a hard time finding square PVC


haha


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## ClinesSelect (Apr 16, 2006)

Depends on the enclosure and what fits/looks better.


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## forty5cal1911 (Sep 11, 2006)

I agree with Cline...depends on the enclosure and your implementation. If you are tuning really low there are some benefits of using a slot type port. In transmission line enclosures (which I'm very fond of) you can wind the port inside the box much easier. Benefits are if you need a long port it's easier than using round pvc with 90 degree elbows, also adds rigidity and bracing to the enclosure, lower port noise if done correctly. All IMHO.


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## backwoods (Feb 22, 2006)

forty5cal1911 said:


> adds rigidity and bracing to the enclosure, lower port noise if done correctly. All IMHO.


 
exactly...Sub ports are the best as slot ports. 

Nothing worse then wondering where that vibration sound is coming from, and realizing it's your port. Inside the box...

That you just sealed up... And can't easily access after you finished your install...


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## ErinH (Feb 14, 2007)

backwoods said:


> exactly...Sub ports are the best as slot ports.
> 
> Nothing worse then wondering where that vibration sound is coming from, and realizing it's your port. Inside the box...
> 
> That you just sealed up... And can't easily access after you finished your install...


Right, but you're assuming you've built the box right the first time with a slot port. So, might as well assume the same for a circle port. In that sense, a circle port is convenient because you can pull the circle out to get something out, maybe a dropped screw, or something along those lines. Can't do that with a slot port.

I do agree with the added bracing, and especially the length of a circle port being an issue. 

Other than that, however, I don't really know if there's a solid _sound_ advantage of the slot over round. 

Just to be clear, I'm not saying one _is_ better than the other, but considering all things equal (net volume, port length, build, bracing, etc) is one truly better or is it just install dependent?

Edit: For me, in general, my designs follow this:
For a large enclosure, circle port since I have plenty of room to run the port. Bracing as needed.
Small enclosure gets slot, since the bends are better.


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## zukiaudio (Jan 31, 2007)

check out pmc speakers

go listen to set if you get the chance.

http://www.thesoundbroker.com/PMC.htm


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## Whiterabbit (May 26, 2006)

Slot for ease of install. use a router for best results:

Most bit sets come with a 1/2 inch round over and a 3/8ths inch rabbet.

so we want to install a round port, 4" PVC schedule 40, its 4" ID, and 4.5 OD. we want to make a perfect fit port. We will cut a hole and rabbet out the backside so the port fits in perfect, then round the frontside over:

3/8ths x2 = .75, and the port is 4.5" OD. so we cut a hole with our circle jig thats 3.75 inches in diameter. a perfect circle.

next, we rout 3/8ths deep out of the backside with our 3/8ths rabbet. the widedned hole back there is 4.5 inches.

now we fit the port in. It'll have to be hammered into place, the fit is so tight. No glue needed.

turn the baffle back over, and the 3.75 inch hole overhangs the port opening by .25 inches. Chuck up the 1/2 inch roundover bit and set the wheel bearing deeper than the overhang. Buzz around the port and you not only flushtrimmed the MDF to the PVC but rounded over the port edge. Poor man's aeroport, and no more whistles.

want to go the extra mile? cut an MDF ring with a 6" OD and 3.75" ID. do the same thing and attach it to the end of the port inside the box.

Want the "slot port" bracing for your PVC? rather than cutting a ring, cut a rectangle so that it fits over the port but also can be glued and stapled to the side of the box. instant additional port bracing while maintaining the aeroport style roundover front and back.
---------------

want 2.5" OD PVC? cut the hole 1.75 inches around.
Want 6" sewerpipe PVC? cut the hole 5.25 inches diameter.




I voted for PVC.


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## ErinH (Feb 14, 2007)

Whiterabbit said:


> Slot for ease of install. use a router for best results:
> 
> Most bit sets come with a 1/2 inch round over and a 3/8ths inch rabbet.
> 
> ...


LOL. That's a whole lotta info.

Any pictures of these installs?


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## chad (Jun 30, 2005)

zukiaudio said:


> check out pmc speakers
> 
> go listen to set if you get the chance.
> 
> http://www.thesoundbroker.com/PMC.htm


Why? You selling a set?

What does that have to do with port shape? Incidentally I like Meyer HD1's better, they have a round port, 2 of them to be exact, but the port area geometry has nothing to do with the sound.

well... Actually it COULD since airflow in the corner areas would have a different resistance, a circle has no corners. 

My next pro subs will be built with slots, it's no biggie but the venting is huge, this wil prove easier with a slot then to cut a kazillion holes for round portage.

Chad


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## BlackLac (Aug 8, 2005)

i just like the look of slots better. also, when people who don't know anything about car audio see it, they're like "WTF".


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## zukiaudio (Jan 31, 2007)

i have noticed most speakers this guy builds have round ports.

Dave Rosgaard


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## Whiterabbit (May 26, 2006)

bikinpunk said:


> LOL. That's a whole lotta info.
> 
> Any pictures of these installs?


nope. Try making one for yourself. You'll see.


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## 300Z (Mar 20, 2005)

I prefer Slot ports just because they help with actual box rigidity when done properly, and I like the way they look better. But with that said on my last ported box I used round ports just because it was easier and the only tools I had at hand to build this box was a jigsaw and a drill.


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## johnson (May 1, 2007)

cannot "see" if the description is hard to follow


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## Whiterabbit (May 26, 2006)

follow the directions step by step, itll work. You'll figure it out as you go.


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## Boostedrex (Apr 4, 2007)

Whiterabbit said:


> Slot for ease of install. use a router for best results:
> 
> Most bit sets come with a 1/2 inch round over and a 3/8ths inch rabbet.
> 
> ...



Very good post. I hadn't even thought about that. It's funny how you can miss the easiest details sometimes.


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## Whiterabbit (May 26, 2006)

slot or round, "attention to detail" carries the day when it comes to praise on an install. And it's often easier to worry about attention to detail when running a round port!

even top 3 SPL competitors at the local level who just have a junky install yet push 160's get glazed over for talent.


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## ErinH (Feb 14, 2007)

^ I wasn't asking for pictures of the process. I was just hoping you had some of the finished product.


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## MadMaxSE-L (Oct 19, 2006)

Thought I read something about slot ports having a higher loss from the friction of air moving through the port(with slot ports having a greater surface area of port wall). 

For the SPL suys, that would(to me) translate to a (however slight) loss of output...


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## guitarsail (Oct 12, 2007)

wow way to dig up and OLD ASS thread....


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## chad (Jun 30, 2005)

guitarsail said:


> wow way to dig up and OLD ASS thread....


Someone probably hit the poll, this brings it to the top.


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## Oliver (Jun 25, 2007)

Took me several minutes to figure out what a circle port was


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## MadMaxSE-L (Oct 19, 2006)

chad said:


> Someone probably hit the poll, this brings it to the top.


Wow, that's probably what happened - I didn't even look at the date of the last post...


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## mjgonegm (Jun 21, 2008)

threads never die on DIY MA huh ?


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## justlooking (Sep 19, 2007)

hahahaha, so now a days, is slot or circle better? hahahaha


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## Dryseals (Sep 7, 2008)

Whiterabbit said:


> Slot for ease of install. use a router for best results:
> 
> Most bit sets come with a 1/2 inch round over and a 3/8ths inch rabbet.
> 
> ...



Very close to how I do mine. I use the Jasper Jig for the holes. Rabbit the back side to fit the PVC. Then cut the hole just a tad less than the the ID of the PVC. I glue in the PVC using a gorilla glue or simular. Epoxy works the best, but but either will do.

Then with a flush trim bit, I clearance the hole to match the PVC. Then quick round over and its done.

I'm not fond of the slots because of all the extra steps needed to make it flow smooth. A short slot is not to bad, but if it need to make a turn then it takes a lot of cuts to make a smooth path for air flow. I used to port engine heads, learned some neat tricks about air flow. Same with transfer lines, using air to move a product through pipe work.

Most folks try to make the port insides smooth, thinking that air will flow smoothly across. In effect yeah, but not so in reality. If the inner layer is dimpled, air will flow smoother. The dipples help develope a skin effect and improve laminar flow through the device. Any corners in the device need to be made to flow smoothly, other wise you develope turbulent flow and in some cases create small vortices. Square edges are hard to make flow smooth.

I built a set of Ariels for my sons room. Modified the tuned path and had some good results. But still a ported design using a round port would be far easier.


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## TrickyRicky (Apr 5, 2009)

This might sound stupid, but everytime I build a ported enclosure, I round-off the edges of the ports. I know that you HAVE to do this to reduce air noise. But most boxes i've seen dont even do that, like some idiot just built the box for a quick 50 bucks.


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## chad (Jun 30, 2005)

you don't HAVE to do it, but when using vents on the smallish side it's a damn good idea.


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## TrickyRicky (Apr 5, 2009)

Have you seen any of PWK's designs? Talk about a nice curved slot port. I think is his horn boxes that have this neat design, and look very neat.


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## chad (Jun 30, 2005)

define horn.

Hint.. we have been over horn loading before here many times.


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## TrickyRicky (Apr 5, 2009)

Well from what i've seen on his designs, the port starts small, and as it turn and exists it gets bigger, and every turn is curved. The outside port which is big, is also curved.


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## TrickyRicky (Apr 5, 2009)




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## chad (Jun 30, 2005)

in order to be a true horn it has to load in the pass-band the speaker is playing in... those flared ports are too small in his designs to be called a horn, it's a fancy flared port.


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## TrickyRicky (Apr 5, 2009)

True.


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## stills (Apr 13, 2008)

how do you guys feel about multiple ports vs. just one?


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## DaveRulz (Jun 22, 2006)

For those that can't picture Steve's (whiterabbit) method, here it is on speakerbuilder.net

http://www.speakerbuilder.net/web_files/Articles/porttut/porttut.htm


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## TrickyRicky (Apr 5, 2009)

stills said:


> how do you guys feel about multiple ports vs. just one?


They work. The John Fairchild enclosure design for the stroker was muilti ported. One triangle port in every corner (4 total). His enclosure measured about 12 cubic square feet for just one 18" Stroker.


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## chad (Jun 30, 2005)

Let's say you have lots of depth to work with but not much face, then multiple vents will work well as you can get the area you need without having to make room for a larger vent. sometimes geometrically multiples are ideal.


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## MoreBassThenSense (Dec 21, 2010)

backwoods said:


> exactly...Sub ports are the best as slot ports.
> 
> Nothing worse then wondering where that vibration sound is coming from, and realizing it's your port. Inside the box...
> 
> That you just sealed up... And can't easily access after you finished your install...


Hahaha sooo true. I was using 3 and a 1/4 inch PVC pipe for a port on my sub box, I even had them lighted  , any my subs shook the box so hard it destroyed super strength wood glue, super crazy glue, even two screws. Anyways my port kept falling down into my nice sealed box and going insane inside it. Not good when you have lights on the inside of the port....  lol But anyways thats somehting that would NEVER happen with a slot port. Mainly cause its built into the box  lol


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## Jmirage (Nov 23, 2010)

I have used slot ports except while competing db drags with a box that stayed in my car all the time. I had (3)4" ports in each enclosure. When it wasn't competition time, I would use the plugs that plumbers use to temporarily seal drains to test them under pressure, that would lower my tuning frequency to something I could listen to on a daily basis.


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## The Tube Doctor (Nov 24, 2009)

I've always used LEAP to model ports. It also allows modelling multiple 
ports, with respect to port-to-port distance & speaker-to-port distance.
You can also get great data on group delay, which gives you an indication 
of how much or how little the ports will "ring".
Highly accurate when fed the appropriate data.

Used another (long gone) program called SPEAK. Used that one under 
an engineer's supervision, as it was a serious head-full.
With speak, you could model planar drag, which is the sort of thing that 
comes into consideration with slot ports. Greater surface area for a given 
port volume has an effect on the resistance of the air flowing through the port.
It can result in unintended eigentone generation. (organ-pipe resonance)

Cutting a port and hoping for good results can be frustratingly random.
There's a wealth of great tools available, provided you don't get bogged 
down in minutiae while trying to think of the right questions to ask.


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