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Discussion Starter · #1 ·
I understand that the trick to ports is keeping the air speed low enough as to not be heard. The remedy to that is either more ports, or larger ports, but then you end up increasing the length. So...


1) What is the port air speed to avoid exceeding? I have heard both 35 ft/sec and 65 ft/sec.


2) How much can polyfill reduce air speed? Any other tricks?


3) Does a port have to be hard, like PVC? Could it be made out of a heavy bendable hose of some sort? It is the air volume that tunes the port, not the material, correct?


Thanks.
 

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Discussion Starter · #4 ·
I have looked at both Linkwitz and have been playing around with WinISD. LTD02, that link was useful, but didn't really answer all my questions (gave me some new insight though).


Anyone else have any ideas about using bendable tubing for ports? How about the measured effect polyfill will have on air speed?
 

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In my opinion you can never tune low enough and you can never have too big of a port diameter. If you want the best sound quality you will use the single largest port you can. My 18" subs use a single port that is 10" in diameter and are tuned to 14 Hz... The best sound quality uses the largest single port you can utilize. You don;t have to flare the port once you ge tthe airpseed 'low-enough'. Instead just focus on making the pot diameter as large as possible.
 

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Quote:
Originally Posted by theater_lover /forum/post/16944567


I have looked at both Linkwitz and have been playing around with WinISD. LTD02, that link was useful, but didn't really answer all my questions (gave me some new insight though).


Anyone else have any ideas about using bendable tubing for ports? How about the measured effect polyfill will have on air speed?

LTD02's link really does answer your biggest question of how big the port and the roundover need to be to not chuff. It tells the max port velocity with the various combos.


Bendable tubing, forget it in the diameters you are looking at. You can buy rigid bends at a plumbing store. Stuffing the port with polyfill will more or less defeat the purpose of the port although you might want to do that in special circumstances -- make Qp much lower in WinISD to simulate it.
 

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Discussion Starter · #7 ·
I guess I have never understood how large diameter ports are possible. If you start with 4" port at say 15" long, you can end up with a 10" port being 200" long (just a guess).

I have seen plenty of users use large diameter ports, but I have never understood how that is possible unless if they used a small diameter port it would be like 1" long... does that make sense or am I missing something?


When I model my design for vented in WinISD, it says I need a 22" long, 4" diameter port. Problem is the air speed is very high. I plan on adding polyfill, but not entirely loose, likely netted off from the port and the drivers.
 

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My Black Hole Subs enclosures are 45"H x 28"W x 44" D per driver ) (4 subs). 10" diameter port tuned to 14Hz. If you increase the size of your enclosure, you can increase the diameter of the port and that will decrease port velocity...
 
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