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Hey guys, its tax time and my pending refund check has me itching for something low and loud! I am trying to decide between a round or slotted port for this sub I will be using an RLP-18 and EP2500/BFD setup. My main question is this: Is there a noticiable difference in sound quality between a round (sonotube type) port and a slot port built into the box of the sub? Thinking of building something on the order of 36"x24"x36", so room isn't an issue for me, just want the best BOOM :bigsmile: for my buck. Thanks!
 

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There is no difference in sound quality of the port type (assuming proper construction), but there are other factors that become involved. For example if the port is so long you cannot fit it in a cabinet in one shot than a slot port is ideal. At the same time slot ports are more complicated to build. It is a trade off, personally I prefer slot ports, but that doesn't mean they are the best. As long as you have sufficent cross-sectional area you will be fine while respecting the boundaries of port resonance.
 

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Round ports will have the least chuffing per cross-sectional area...slots ports have the most. You also gotta watch out for extra resonances with slot ports too. Bends also increase chuffing (for both kinds of ports). That's not to say they can't be done, but it's not necessarily a free lunch.
 

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Right - if you have the space for a cylindrical port, that's the route to take - less turbulent air flow.

Will it result in a noticable difference in sound quality? Probably not, but it will allow for higher air speeds before chuffing assuming the same cross sectional area.
While it is most likely the case that slightly less turbulence will occur comparing slot port to a straight round one with longer ports this is at the cost of decreased backwave resonance. Because round ports will require a longer box it is far more likely to cause excitation of a backwave resonances in the passband compared to a slot port. Of course, if the cabinet is reasonable in size proper damping can be used to eliminate such an issue. As with virtually all aspects of design different types have their limitations and strengths.
 

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And then there's the passive radiator...best of all worlds ;)
(provided you can keep the suspension linear)
 

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I built a set of stereo speakers for my daughter a couple years ago, and used a slot port because I was concerned about the kids "losing" things inside the speaker if it was a round port. A couple years later I was talking with my Aunt and she told a story about her granddaughter walking past Dad's speakers and saying "uh oh, uh oh...".
Using the slot port, my grandson can even use it for a garage, and toys won't be lost.

Add this in edit:
Oh yeah, form an entirely personal aesthetic point, I hate the look of a big hole on the front of a speaker. All my own ports are either down-firing of rear-firing.
 

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You know I'm surprised that you don't see more PR's utilized in full range designs. In a SW application the port resonances are largely a non issue but in a fullrange speaker they are in the pass band and careful attention has to be paid to deal with them. Using a PR would remove this issue largely and also allow a slightly smaller enclosure. Manufacturing costs I guess.
 

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You know I'm surprised that you don't see more PR's utilized in full range designs. In a SW application the port resonances are largely a non issue but in a fullrange speaker they are in the pass band and careful attention has to be paid to deal with them. Using a PR would remove this issue largely and also allow a slightly smaller enclosure. Manufacturing costs I guess.
I don't know of any except the ones put out by Klipsch in the 80's. I love my Chorus II's (15" active, 15" passive).
 
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