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Old 08-04-2014, 04:18 AM
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Default Calculating vent length

I used the car stereo dot com vent length calculator, then the 12 volt calc, then another one. They all come out different.


How long would my port need to be if my port area was 127.5, my box was 8 cu ft. Net, and my desired freq was 45-46hz?

Can anyone help with the "correct" length? Thanks in advance.

Please also tell me how you achieved this. Thanks
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Old 08-04-2014, 05:18 AM
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Were they round or square calcs?
Sure you didn't choose slot vs square?
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Old 08-04-2014, 05:23 AM
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Square
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Old 08-04-2014, 05:24 AM
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Wait I will check. Lol
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Old 08-04-2014, 05:37 AM
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Not sure what I would use? Square or slot. I am using a wall as part of the port. But it is not going to be long enough to make the 90 degree turn.
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Old 08-04-2014, 05:46 AM
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I think the issue comes from two things: (1) accounting for the displacement of the port volume and (2) slot/boundary corrections. When you enter in the rectangular dimensions it uses one of them to calculate effective length, but usually there's no easy indication of which one it uses. Sometimes you can get a different length if you enter in "12.75 x 10" instead of "10 x 12.75".

I get anywhere between 17.2" and 17.8" for a 44hz tune with the port flush on the outside of the enclosure, and completely free from any boundary walls inside the enclosure. The slight variation is due to volume displacement from the port walls. I'm using BassBox for those numbers. There's several variables that can change it +- an inch or so, like if part of the port is external, if you're using double baffled port walls, if your port shares a boundary wall, etc...

From running impedance sweeps on a few of the enclosures I've built, tuning is always lower in-car than you would expect based on calculations, but not by a predictable amount. In the end the best you can do is get close.
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Old 08-04-2014, 06:32 AM
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Calculators are off all the time
And if it's by a wall it will use a portion of the corner it's closest to depending how close
But it's not really needed to be accurate on port unless you are chasing the tenths on the meter
You can be off by a few inches and only change the port a few hz
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Old 08-04-2014, 06:34 AM
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I'm doing a wedge box in an ext cab pickup, port facing up on the drivers side. So actually 2 walls are used, back and drivers side. Those calcs either gave me 6.xx or 11.xx. Now you are giving me 27.xx
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Old 08-04-2014, 06:36 AM
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17.xx *
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Old 08-04-2014, 06:38 AM
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Default Calculating vent length (picture for reference)

Port will be top drivers side

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Last edited by stealth; 08-04-2014 at 06:41 AM.
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