different port diameters in a single subwoofer box? - Page 2 - diyAudio
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Old 25th September 2011, 12:30 AM   #11
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but thats not the same thing.

it sounds like you had the same port area for both ports, but different lengths.
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Old 25th September 2011, 12:39 AM   #12
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Default two ports different lengths

Quote:
Originally Posted by ThyDntWntMusic View Post
what exactly did you try?
Hi there: I recall reading an article in "Strings Magizine", where a professor was reproducing music with a box speaker enclosure with ports of different lengths. The ports shown in a picture, were external to the box (probably for ease of tuning). There were no details for the box, drivers or ports, however the results were discribed as amazing. So as usual, our new ideas have been considered by others in the past. ...regards, Michael
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Old 25th September 2011, 12:53 AM   #13
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Yes,I see your point and I am not sure about the math that is causing this.
But the diference in tuning in the example is a rise by .7 hz for using two ports.
Also the area of 2 X 3.535 is slightly smaller than a 5"dia. tube.
This could account for maybe .5%.
A difference of only 2% to 3% total between the two.
Something that will doubtfully be heard by ear anyhow, As it is a difference of less than .2db on the peak in this particular example.
I will look more into this in the future and see what else I can find on the subject.

jer
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Old 25th September 2011, 12:57 AM   #14
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The two ports were 3"dia and 4"dia both 22" long in a 4ft^3 box
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Old 25th September 2011, 01:03 AM   #15
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this page has a good description of what's going on.

JL Audio - Car Audio Systemsd

edit: basically more ports = more friction loss which rases tuning, so you have to make the ports longer to compensate.

Last edited by revboden; 25th September 2011 at 01:07 AM.
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Old 25th September 2011, 01:15 AM   #16
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Great Link!
I do recall reading about that,But I never knew how much of a factor it is.
I will read it more throughly later tonite so that I can fully understand it.

jer :
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Old 25th September 2011, 09:51 AM   #17
ODougbo is offline ODougbo  United States
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I’m a bass reflex junky and have tuned many a speaker. You can certainly experiment with 2 different ports but agree with the consensus. You would be better off with a second speaker/box and tune it a different frequency. Additionally, I’ve had way better results with slotted ports.

This works well, and actually easier than round ports:

semi build the box, to the point where the front baffle board and “slot” (glued together like an “L”) can be slid up and down, which changes the port’s area/volume - using a generator/volt meter you can tune the box and then do the final glue up; you’ll need a good number of clamps. A dry fit, so to speak.
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Old 27th September 2011, 02:35 PM   #18
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Quote:
Originally Posted by revboden View Post
plug this into winisd
open two project boxes with the same driver ported 2.5ft^3
first project with one port 5" diameter 18.84"
second with two ports 3.535" diameter
they have the same cross area but the box with two ports will be longer by an inch
just wondering did you ever actually build a box to see if the predictions in the program came out to match the actual f b,with the added 1". Just to see if the program was correct?
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