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vent length not given in WINISD means?
vent length not given in WINISD means?
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Old 4th October 2019, 02:40 AM   #1
cT equals piD is offline cT equals piD  United States
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Default vent length not given in WINISD means?

In a QB3 alignment cooked up by WINISD for a 4 inch driver, the alignment calls for box volume equal to 4.42 liters, a tuning frequency of 65.6 Hz (Fs = 60 Hz), a vent diameter of 10.2 cm, and length of the vent is blank.

Based on calculations that I did for this driver in a vented alignment, the fact that vent length is blank in the alignment by WINISD I would think means that the corresponding vent length is very short and thus is not given.

Does this mean that in building the box that the system will work correctly so long as the vent length is very small, say 3/4 inch or less, or must the vent length be smaller than that?
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Old 4th October 2019, 05:54 AM   #2
Sonce is offline Sonce  Macedonia
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Something is very, very wrong! With such a small box volume, relatively low tuning frequency, and a large vent diameter, vent length should be over 1 yard!
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Old 4th October 2019, 08:54 AM   #3
kimmosto is offline kimmosto  Finland
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Maybe program assumes that vent have to fit inside net volume of the box. That's quite difficult for 10.2x121 cm vent if available volume is limited to 4.42 liters. 10.2 vent is overshoot for 4" driver anyway so this would not be serious issue.
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Old 5th October 2019, 12:46 AM   #4
cT equals piD is offline cT equals piD  United States
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Quote:
Originally Posted by Sonce View Post
Something is very, very wrong! With such a small box volume, relatively low tuning frequency, and a large vent diameter, vent length should be over 1 yard!
Yes, I made an error of math in calculating vent length with a formula from Dickason's Loudspeaker Cookbook. Fixing the error, I calculated 120.65 cm for the vent length.

Also WINISD is giving a vent length, but in grayish or faded type, that is, much lighter than for example the tuning frequency. Does anyone know what showing the vent length in lighter type means in the program?

Thanks,
Pete
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Old 5th October 2019, 07:14 PM   #5
cT equals piD is offline cT equals piD  United States
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Default small increase of Qts does the trick

If Qts of the driver is increased from it's normal Qts of 0.38 to 0.47 by connecting a small resistor in series with it, then dimensions of the vent become much more reasonable. This also results in Vb equal to double Vas which is not excessively large, but large enough to accommodate a vent of several inches long.

A vent that I have on-hand measuring 1-5/8 inch diameter and 5 inches long is supposedly acceptable for the alignment that becomes Super QB3.

If anyone wants further details, let me know.
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Old 6th October 2019, 10:37 AM   #6
soundoutlad is offline soundoutlad  Ireland
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vent length not given in WINISD means?
Quote:
Also WINISD is giving a vent length, but in grayish or faded type, that is, much lighter than for example the tuning frequency. Does anyone know what showing the vent length in lighter type means in the program?
I wonder if WINSD has downloaded or is operating properly. I found a similar situation, entering different port values made no difference, in any event I opted for a vented (aperiodic) design, so port wasn't an issue. I'm a relative newcomer to all of this so it could easily be something I'm doing wrong.
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Old 7th October 2019, 04:18 AM   #7
cT equals piD is offline cT equals piD  United States
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Quote:
Originally Posted by soundoutlad View Post
I wonder if WINSD has downloaded or is operating properly. I found a similar situation, entering different port values made no difference, in any event I opted for a vented (aperiodic) design, so port wasn't an issue. I'm a relative newcomer to all of this so it could easily be something I'm doing wrong.
Thanks for the feedback. If both of us see the vent length in faded type, then probably that is the way that the program has been arranged to function, whatever the reason.

-Pete
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Old 7th October 2019, 08:41 AM   #8
mondogenerator is offline mondogenerator  England
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I think this is just because the vent length exceeds the box dims.

Alternatively, it may be because the vent mach figure is over range.

Maybe try reducing port CSA until length becomes manageable?
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Old 7th October 2019, 08:30 PM   #9
cT equals piD is offline cT equals piD  United States
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Originally Posted by mondogenerator View Post
I think this is just because the vent length exceeds the box dims.

Alternatively, it may be because the vent mach figure is over range.

Maybe try reducing port CSA until length becomes manageable?
No, I tried "building" a reasonable vented system with WINISD and the vent length was still given in the same light-colored (gray) type.
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Old 8th October 2019, 05:25 PM   #10
kimmosto is offline kimmosto  Finland
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What is the driver? Thiele/Hoge/Bullock -table alignments have certain limited range for Qts. Alignment fails if Qts is too low or high. WinISD might use some other method than simple interpolation from data table so limits might be difficult to notice without clear error message.
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