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Old 13th October 2012, 03:30 PM   #1
panduro is offline panduro  Denmark
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Default port diameter vs port lenght

redoing my 3, 12inch subwoofers, this time trying(harder) to get it right

they will handle almost everything below 100hz as my satelittes dies pretty fast below that.

as i want to keep the port speed below 10m/s, i would like to use two 4.33inch ports, which with the chosen tuning would need a port lenghts of 26 inches


would this port lenght give me noise(pipe resonance?) when blending the woofers with the satelittes from 150hz to handeling almost everything from 100hz and below?

Please educate me


best regards

panduro
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Old 13th October 2012, 04:17 PM   #2
AndrewT is offline AndrewT  Scotland
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download winisd pro.

It is easy to use and give good plots.
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Old 13th October 2012, 04:49 PM   #3
panduro is offline panduro  Denmark
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thanks for your answer.
winisd pro doesnt work on a mac.

best regards

panduro
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Old 13th October 2012, 04:56 PM   #4
DrDyna is offline DrDyna  United States
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This might help you get WinISD running in OSX:

WineBottler - Run Windows Programs directly on OS X
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Old 13th October 2012, 05:26 PM   #5
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by panduro View Post
..........winisd pro doesn't work on a mac.
buy a cheaper computer.
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Old 13th October 2012, 06:04 PM   #6
tvrgeek is offline tvrgeek  United States
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Flairs will reduce port length as well as allow slightly smaller diameter without chuffing.
I have never had a problem with corners in my ports. Only done a few as I usually do sealed low Q subs.

If you are trying to cross over at 100 to 150, I sure hope your subs are two cabinets used as main speaker stands, or you will have way too much sub localization. 80 Hz at LR4 is about as high as one can get away with. 65 is much better, but above many small bookshelf speakers. It is a bad service that THX set 80 Hz third order as a standard, as it just does not work well enough. 80 at LR6 is almost bearable.
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Old 13th October 2012, 06:18 PM   #7
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by panduro View Post
redoing my 3, 12inch subwoofers, this time trying(harder) to get it right
specs ?
maybe you have tuned too low

with a 4" port ? my length limit would be 12"
I see now you want two 4" ports
one 4" port each woofer should be ok, if not too long
or are all 3 in the same box ?
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Old 13th October 2012, 06:30 PM   #8
panduro is offline panduro  Denmark
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DrDyna: thanks, it works

AndrewT: please explain how buying a new computer would be cheaper

Tvrgeek: flaring the port will reduce port lenghts? i thought it was the other way around as the flaring "doesnt" count in the tuning.

best regards

panduro
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Old 13th October 2012, 06:59 PM   #9
panduro is offline panduro  Denmark
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3 enclosures with one woofer in each enclosure, all placed between the main speakers.


jbl le120h1 no ts published, im told im suppose to model it as a jbl 128h.

jbl 128H fs 20, qts .024, qms 7, qes 0.24, vas 280.4, pe 100, xmax 7.87, re 5.7, le 0.6, sd 0.053, bl 16, mms 90.

jbl recommend 2,5ft3(71L) with a 30hz tuning.

winisd

71L
30hz
one 4.33inch port- 13.8" long- port velocity 16m/s
two 4.33 inch ports- 32" long- port velocity 8m/s


100L
30hz
one 4.33" port- 8.66" long - port velocity 20m/s
two 4.33" ports- 21" long - port velocity 10m/s


i really dont want port chuffing, is 2 x 4.33" ports per 12" woofer overkill? how long can a port be before it damages the sound?

best regards

panduro

Last edited by panduro; 13th October 2012 at 07:04 PM.
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Old 13th October 2012, 10:37 PM   #10
tvrgeek is offline tvrgeek  United States
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Quote:
Originally Posted by panduro View Post
DrDyna: thanks, it works

AndrewT: please explain how buying a new computer would be cheaper

Tvrgeek: flaring the port will reduce port lenghts? i thought it was the other way around as the flaring "doesnt" count in the tuning.

best regards

panduro
A straight pipe with a sharp edge has the effect of causing a restriction at the exit ( of course, both ends are exits. ) The best description of this I read was in a David Vizzards book on tuning A series BMC engines as it relates to velocity stacks. Fluid dynamics does not know if it is a speaker or car. Anyway, play with a sim program and see what the change in port terminus does. WinISD ( there we go again) can do that.
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