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Hey guys,

Doing a new enclosure for the HT sub, working with 16 cubic feet and wanting to do 1 8" downfiring port to 15Hz. ISD says a standard port is going to be 31.5" long...

Could anybody give me a calculation for a power port or even the program and i'll do it myself.

Thanks!
Nick Morgan
Fi Audio
 

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This is a rough description of it. It is a little more than just a simple flared port.


The port system is based on one devised and patented by Polk audio in the mid nineties. They had a nice write up about it in Audio magazine(RIP) in May 96 and offered a simple calculator that they had devised for it and other plans for people to DIY the port system with. Basically the principle is that you increase the port mouth area through expansion and lower the tune. It supposedly offers much better laminar air flow capability and since there is no straight line path to the outside of the enclosure it also helps with port resonance. See the 2 pics below the first is a normal port and the mouth is highlighted green. The second one is this design and the mouth is now the entire circumference of the area highlighted in red and green.









Everyone I discuss this with seems to say "Oh that's nothin special, I don't understand how it's going to accomplish that,or it's just a waste of time". Normally to tune a 10" vent to 11hz in an enclosure this size it would be 62.5" long. This vent, if it works as proposed will accomplish, that same tune with a straight length of only 36.5" and at the same time increase the port area at the mouth to the equivalent of a 14.8" diameter port. I've read the patent papers and am confident it will work. Also have you ever heard of placing your ports close to a panel to get a lower tune? Many of the top sub designers will use this technique( the EPIK Conquest and SVS Ultra13 both do). So much for keeping your ports at-least one circumference from any walls huh? I think this is also involved here with the distance of the disks. It is more than I can explain. If you really are interested have a look at the patent papers.

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It's between 11 and 11.5hz. Right where predicted. Verified with impedance measurements more than once and also through close mic driver and port measurements. If I do a set of sine waves the drivers minimum motion point is easily seen. Nathan Funk also verified it.
 

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Hello all,

I am new to this forum, I'm a Hugh audio enthusiast, I want to Build a power port for a system at home. Is there anywhere I can get the program that Polk Audio had. Like Ricci has.

Thank you

Paul
 
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