Power Port Calculations? - Home Theater Forum and Systems - HomeTheaterShack.com

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post #1 of 11 Old 02-06-09, 06:15 PM Thread Starter
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Power Port Calculations?

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
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post #2 of 11 Old 02-06-09, 08:57 PM
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Re: Power Port Calculations?

A Power Port is nothing more than a normal port with a flare on each end.

http://www.subwoofer-builder.com/port-flares.htm
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post #3 of 11 Old 02-07-09, 05:02 AM
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Re: Power Port Calculations?

Quote:
Pinhead-227 wrote: View Post
A Power Port is nothing more than a normal port with a flare on each end.

http://www.subwoofer-builder.com/port-flares.htm
I'm pretty sure Nick is referring to the Power Port software from Polk Audio that is no longer available. I believe Ricci has a copy of the software and used it for his R.E Audio 18XXX sub build.

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post #4 of 11 Old 02-07-09, 07:15 AM
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Re: Power Port Calculations?

Does this software do something that WinISD does not?


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post #5 of 11 Old 02-07-09, 09:11 AM
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Re: Power Port Calculations?

It determines the port air speed depending on what size of Power Port is used. A description of the process can be found in post #49.

http://www.hometheatershack.com/foru...r-build-2.html

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post #6 of 11 Old 02-07-09, 01:47 PM
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Re: Power Port Calculations?

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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post #7 of 11 Old 02-08-09, 01:51 AM
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Re: Power Port Calculations?

Josh, did you ever determine how close the tuning was to predicted tuning on your XXX18 sub with the Power Port?

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post #8 of 11 Old 02-08-09, 10:55 AM
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Re: Power Port Calculations?

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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post #9 of 11 Old 02-08-09, 12:47 PM
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Re: Power Port Calculations?

Could we get some pictures of the final product? Seems pretty interesting.
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post #10 of 11 Old 02-08-09, 01:13 PM
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Re: Power Port Calculations?

Post 34 and 43:

http://www.hometheatershack.com/foru...r-build-2.html

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