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Discussion Starter #1 (Edited)
Just curious if anyone has ever done a 'spiral' shaped port before? I have something sketched up but I can't post the pic until they update my account. I know that round ports are preferred, but this style of port would give you the most length with the smallest enclosure dimensions. Any pros or cons to this approach? (I will upload the sketch as soon as I get permission).

This is a basic pic to get the idea across - this port could be added on either side of a regular box to give you 2 - 6x6 ports approx 89.5 inches long. If you needed longer you could theoretically continue the port inside the box or put two back to back. Just brainstorming ideas
 

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by spiral port do you mean something along the lines of a corkscrew? I hadn't thought about that before but I don't see any reason why that wouldn't work as a means of getting a longer port into a smaller box, though i'd want to make sure the flares on either end were large enough to prevent backpressure loading the port.
 

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Discussion Starter #3
yes - like a sea shell, but constant diameter throughout. My sketch has the entrance near the middle and spiraling out from there. In theory you could even do two spirals together or extend the entrance to get a REALLY long port in a small box. It would be a pain to build, but should be extremely strong.
 

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yes - like a sea shell, but constant diameter throughout. My sketch has the entrance near the middle and spiraling out from there. In theory you could even do two spirals together or extend the entrance to get a REALLY long port in a small box. It would be a pain to build, but should be extremely strong.
It has been done. Very long ducts give rise to resonances, so there is a point where too long a duct becomes counterproductive and you're better off going with a larger box instead.
 

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Discussion Starter #6
Thanks Bill,

I figured somebody had tried it before, but didn't see any designs similar to it online other than some REALLY high end speakers that looked like sea shells. Anyway - it looked like a neat variant to give more options on design - squeezing the biggest port into the smallest size. I realize you would have to still look at how it worked out in each application, I just didnt' know if making that many bends is a no-no or if people just shyed away from it because of the complexity of the design and build.
 

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impressively long port in a smallish footprint, but like bill said, the downside being a first resonance of about 67 Hz! though there are certainly port dimensional compromises that can be made to keep resonances out of the active bandwidth and get you the tuning frequencies desired.
 

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Discussion Starter #10
I see now what you guys are referring too - I was playing with WINISD and had a few configurations with ports up to 75 inches long and do to the shape of my box that would require at least 2 bends in my port. I came up with the spiral port thought and didn't know if it could be used in designs with drivers much smaller than the one I am designing or tuned to a higher frequency. I have also seen some designs online for smaller drivers with long ports that are compressive (ie they start large and get smaller toward the outlet). Just seeing if there was any merit in that type of design - thanks for answering my question.
 

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With a 101 inch duct you no longer have a bass reflex cab, you have a transmission line with a 35 Hz fp. The longest practical duct length is about two feet.
 
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