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Old 28th June 2013, 02:00 AM   #3571
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Quote:
Originally Posted by tb46 View Post
Hi David,

Thanks again for you effort it is very much appreciated.

Looking at Bagby's software (Woofer Box Model and Circuit Designer, Version 4.5 12/4/2009) again, it looks like I may have found the basic error: when switching the "Selectable Textbook High Pass Filter" from "Fourth Order Butterworth" to "Fourth Order Linkwitz-Riley" there is no change in the "Circuit Shape" as indicated on the graph; but, when using both of the "Optional Second Order Adjustable High Pass Filter Stages" @ Fc=24Hz Q=0.707 [Gain(dB)=-3.0dB] I get the expected 4th order LR response on the graph. The LP section also shows the same curve for Bw and LR. In other words, I think I may have found a bug (or two) in Bagby's spreadsheet, not in Hornresp.

I'll attach a few screenprints:

1. Bagby's Input screen
2. BP: Dual 2nd order Butterworth HP plus 4th order LR LP
3. BP: 4th order LR (both: HP and LP)
4. HP: 4th Bw
5. HP: 4th LR
6. HP: 2x 2nd Bw
7. SPL w/o filters
8. I'll tried to add Bagby's Excel file by changing the extension from .xlsm to .txt; but, the file size is too big (I can email it to anyone interested).

So, at this time it looks to me like all is well in Hornresp land.

Regards,

P.S.: Just downloaded and tested Baby's Version 5.0, same result as Version 4.5.
I suspect you are not clicking the "Load Low Pass" button and only scrolling to the crossover type of your choosing. If you don't click that command button it will not load the crossover transfer function coefficients you have selected and you will simply have whatever transfer function was previously loaded. Try that and let me know if that's all it was. I know I can see the difference between LR and BW when I do this.

Jeff B.
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Old 28th June 2013, 02:35 AM   #3572
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Hi Andrew,

Quote:
Originally Posted by AndrewT View Post
Ah, I get what you have been trying to describe.
I had a feeling that we would get there eventually :-).

Quote:
Originally Posted by AndrewT View Post
A bandpass filter that has NO passband !
Why ?
As indicated in my initial post, the whole exercise was a sanity check only - it was not intended to have any practical application. In the light of Oliver's earlier comments I simply wanted to make sure that the high-pass and low-pass filters were combining correctly when used together as a band-pass filter. One easy test was to confirm that the overall response at a common 100 Hz cutoff frequency was -6dB for a Butterworth BPF (-3dB due to the HPF and -3dB due to the LPF), and -12dB for a Linkwitz-Riley BPF (-6dB due to the HPF and -6dB due to the LPF). The results did indeed show this.

Kind regards,

David
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Old 28th June 2013, 03:03 AM   #3573
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Quote:
Originally Posted by Jeff B View Post
I suspect you are not clicking the "Load Low Pass" button and only scrolling to the crossover type of your choosing. If you don't click that command button it will not load the crossover transfer function coefficients you have selected and you will simply have whatever transfer function was previously loaded. Try that and let me know if that's all it was. I know I can see the difference between LR and BW when I do this.

Jeff B.
Hi Jeff,

In the light of Oliver's comments in Post #3552, I would be very interested to know if you see any problems in the active filter response results produced by Hornresp. Thanks.

Kind regards,

David
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Old 28th June 2013, 02:44 PM   #3574
tb46 is offline tb46  United States
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Hi Jeff B,

Post #3571: "... suspect you are not clicking the "Load Low Pass" button and only scrolling to the crossover type of your choosing. If you don't click that command button it will not load the crossover transfer function coefficients you have selected and you will simply have whatever transfer function was previously loaded..."

You are indeed correct, somehow I totally overlooked the "Load ... Pass" buttons. I found the ON/OFF buttons, and the DISABLED/ENABLED button, but not the LOAD buttons.

While I have your attention, sometimes the spreadsheet seems to hang with all graphs devoid of data lines, and sometimes it does not want to recalculate; only leaving the program, and reopening helps. Just more operator problems, or "normal" Microsoft behaviour? I'm running a Windows XP SP3 laptop.

Generally, I really like your simulator, and it's results seem to track closely with Hornresp (given a competent operator). :-) Thank you so very much for looking into this.

Regards,
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Last edited by tb46; 28th June 2013 at 02:49 PM.
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Old 28th June 2013, 02:50 PM   #3575
tb46 is offline tb46  United States
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Default Post #3573

Hi David,

While your question is directed at Jeff B, I just want to add that after properly using Jeff's software the resultant curves now look a lot like the ones generated in Hornresp.

Thanks again for your efforts.

Regards,
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Old 29th June 2013, 02:04 AM   #3576
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Quote:
Originally Posted by David McBean View Post
Hi Jeff,

In the light of Oliver's comments in Post #3552, I would be very interested to know if you see any problems in the active filter response results produced by Hornresp. Thanks.

Kind regards,

David
Judging by the screenshots shown on the last few pages, they all appear correct to me. Are you using a polynomial and just changing coefficients for different crossover orders and shapes? That what mine does. I use the same equation whether it's a 1st order Butterworth or an 8th order LR. I just use a table that drops the coefficients in based on the selection and it creates the transfer function shape.

Jeff
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Old 29th June 2013, 02:09 AM   #3577
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Quote:
Originally Posted by tb46 View Post
Hi Jeff B,

Post #3571: "... suspect you are not clicking the "Load Low Pass" button and only scrolling to the crossover type of your choosing. If you don't click that command button it will not load the crossover transfer function coefficients you have selected and you will simply have whatever transfer function was previously loaded..."

You are indeed correct, somehow I totally overlooked the "Load ... Pass" buttons. I found the ON/OFF buttons, and the DISABLED/ENABLED button, but not the LOAD buttons.

While I have your attention, sometimes the spreadsheet seems to hang with all graphs devoid of data lines, and sometimes it does not want to recalculate; only leaving the program, and reopening helps. Just more operator problems, or "normal" Microsoft behaviour? I'm running a Windows XP SP3 laptop.

Generally, I really like your simulator, and it's results seem to track closely with Hornresp (given a competent operator). :-) Thank you so very much for looking into this.

Regards,
I have not ran across anything odd with this program on different computers and it seems to work great on my old XP machine with Office 2000. My Passive Crossover Designer can get a little funky sometimes in Office 2010, and none of my stuff works with a 64 bit Office application. You can thank Microsoft for that, they changed how the VBA works for the 64 bit and it won't compile my VBA modules correctly and shoots back a bunch of errors. I am not going to rewrite things at this point, so I guess that's life.
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Old 29th June 2013, 03:05 AM   #3578
tb46 is offline tb46  United States
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Default Post #3577

Hi Jeff B,

I experimented some more today, and the main "hang up" seems to occur immediately after saving. The curves disappear from the graphs, and won't come back. The different F9 recalculation key combinations won't bring it back, and the easy work-around is to close, and re-open the program. Not a big problem, as the last information seems to be saved.

I can fully understand, that you don't want to "rewrite things". I wouldn't either. Thanks again for a very useful program.

Regards,
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Old 29th June 2013, 06:17 AM   #3579
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Quote:
Originally Posted by tb46 View Post
While your question is directed at Jeff B, I just want to add that after properly using Jeff's software the resultant curves now look a lot like the ones generated in Hornresp.
Hi Oliver,

Excellent, many thanks for confirming this.

Kind regards,

David
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Old 29th June 2013, 06:27 AM   #3580
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Quote:
Originally Posted by Jeff B View Post
Judging by the screenshots shown on the last few pages, they all appear correct to me. Are you using a polynomial and just changing coefficients for different crossover orders and shapes?
Hi Jeff,

Thanks for confirming that the Hornresp results look okay.

I use the following expressions to calculate the normalised gain G at frequency f where fc = filter cutoff frequency and n = filter order.

Low-pass Butterworth:

G = 1 / Sqrt(1 + (f / fc) ^ (2 * n))

High-pass Butterworth:

G = 1 / Sqrt(1 + (fc / f) ^ (2 * n))

Low-pass Linkwitz-Riley:

G = 1 / (1 + (f / fc) ^ n)

High-pass Linkwitz-Riley:

G = 1 / (1 + (fc / f) ^ n)

I calculate band-pass gain simply by multiplying the appropriate high-pass and low-pass gains together.

Kind regards,

David
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