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vent length not given in WINISD means?
vent length not given in WINISD means?
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Old 9th October 2019, 12:50 AM   #11
cT equals piD is offline cT equals piD  United States
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Quote:
Originally Posted by kimmosto View Post
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.
The driver is MCM 55-1853, Newark Element 14. This is a 4 inch driver with

Fs= 60 Hz
Qts = 0.38

It you increase Qts to 0.47 by putting a resistor in series with the voice coil of the driver, then it can be configured SQB3 and the vent dimensions become reasonable. In testing this with WinISD, the vent length is still sort of faded, but still legible if you look closely.
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Old 9th October 2019, 02:16 AM   #12
tsmith1315 is offline tsmith1315  United States
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Nothing odd there, the Qts is great for a vented box.

@ 5 liters & 60Hz, a 1" dia port would be ~6" long
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Old 9th October 2019, 05:49 AM   #13
kimmosto is offline kimmosto  Finland
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I don't find anything suspicious here. Lame outlooks of few text boxes is just style of read-only fields.
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Old 9th October 2019, 08:23 AM   #14
David McBean is offline David McBean  Australia
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Quote:
Originally Posted by tsmith1315 View Post
@ 5 liters & 60Hz, a 1" dia port would be ~6" long
Attachment 1 shows the power response of a bass reflex loudspeaker having the above dimensions and a MCM 55-1853 driver. The fundamental resonance frequency of the system is closer to 40Hz than the desired target value of 60Hz. Attachment 2 shows the "flatter" power response obtained by simply doubling the port tube cross-sectional area Ap to move the fundamental frequency closer to the required 60Hz.
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File Type: png Attach_2.png (57.1 KB, 68 views)
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Old 9th October 2019, 12:16 PM   #15
tsmith1315 is offline tsmith1315  United States
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Hmmm... Yep, thanks David. That would have been 1" dia and 6 cm @ 5L and 60Hz, I didn't convert the length to inches. The pitfalls of doing things manually- I should be more careful before posting. Sorry!
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Old 9th October 2019, 01:02 PM   #16
David McBean is offline David McBean  Australia
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Quote:
Originally Posted by tsmith1315 View Post
That would have been 1" dia and 6 cm @ 5L and 60Hz
Hi Tim,

That's better :-).

Kind regards,

David
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Old 10th October 2019, 12:34 AM   #17
cT equals piD is offline cT equals piD  United States
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Quote:
Originally Posted by tsmith1315 View Post
Nothing odd there, the Qts is great for a vented box.

@ 5 liters & 60Hz, a 1" dia port would be ~6" long
The problem with the 1 inch dia. vent is that this is slightly less than the minimum diameter required to avoid power compression. A 2 inch diameter vent would be much better.

In your configuration, I think you mean that the vent would be about 6.5 cm long.
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Old 10th October 2019, 01:58 AM   #18
cT equals piD is offline cT equals piD  United States
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Quote:
Originally Posted by tsmith1315 View Post
Nothing odd there, the Qts is great for a vented box.

@ 5 liters & 60Hz, a 1" dia port would be ~6" long
Another problem that I have with your alignment is that in the books that I've read about the vented system, the different methods for arriving at box volume are based on Qts of the driver.

For example, looking at the alignment charts in Dickason's Cookbook, all of the different alignments (BB4, QB3, SC4) show box volume less than Vas where Qts equals 0.38. In your alignment, you set box volume equal to Vas.
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Old 10th October 2019, 05:07 AM   #19
kimmosto is offline kimmosto  Finland
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^Table alignment is just one possible starting point you don't have to accept and build. Quite many extend frequency range by increasing volume and lowering HH resonance compared to table alignments. Also net volume losses due to vent and driver are commonly added to proposed volume by table alignment.

If you want to use tool aligning initially with traditional tables by Thiele/Hoge/Bullock, try e.g. VituixCAD. Here is your MCM with QB3 Ql=7.0. MCM is already in online database.
Click the image to open in full size.

Last edited by kimmosto; 10th October 2019 at 05:24 AM.
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Old 10th October 2019, 10:16 PM   #20
tsmith1315 is offline tsmith1315  United States
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Quote:
Originally Posted by cT equals piD View Post
In your configuration, I think you mean that the vent would be about 6.5 cm long.
Exactly. My bad, that length was calculated in cm and should have been converted to inches like the dia. before posting.

Quote:
Originally Posted by cT equals piD View Post
Another problem that I have with your alignment is that in the books that I've read about the vented system, the different methods for arriving at box volume are based on Qts of the driver.
That is a TBG™ alignment*. By definition, this alignment must be determined within a few seconds without software or charts, only eyeballs and noggins allowed. Facial grimacing is acceptible if it helps.

While the above is true, I wasn't suggesting an alignment. The numbers were just a quick manual check to see if any results may be unusual enough to explain your software troubles. Drivers with Qts near 0.4 tend to work well in enclosures near Vas size with Fb near Fs, so that's what I used.

BTW, it's nice to see someone actually reading for knowledge instead of just depending on software for answers.

* Tim's Best Guess™
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